text:
The electron and ion Kappa-indices affect the values of the effective Debye length and DH potential at fixed values of r = 0.2, η = 10−3, and Zd0 = 300.
\r\n\tThe applications are those related to intelligent monitoring activities such as the quality assessment of the environmental matrices through the use of innovative approaches, case studies, best practices with bottom-up approaches, machine learning techniques, systems development (for example algorithms, sensors, etc.) to predict alterations of environmental matrices. The goal is also to be able to protect natural resources by making their use increasingly sustainable.\r\n
\r\n\tContributions related to the development of prototypes and software with an open-source component are very welcome.\r\n
\r\n\tThis book is intended to provide the reader with a comprehensive overview of the current state of the art in the field of Ambient Intelligence. A format rich in figures, tables, diagrams, and graphical abstracts is strongly encouraged.",isbn:"978-1-83969-069-3",printIsbn:"978-1-83969-068-6",pdfIsbn:"978-1-83969-070-9",doi:null,price:0,priceEur:0,priceUsd:0,slug:null,numberOfPages:0,isOpenForSubmission:!0,hash:"3fbf8f0bcc5cdff72aaf0949d7cbc12e",bookSignature:"Dr. Carmine Massarelli",publishedDate:null,coverURL:"https://cdn.intechopen.com/books/images_new/10391.jpg",keywords:"Embedded Systems, Technologies, Sensors, Remote Sensing, Smart Homes, Smart Cities, Integrated Monitoring Techniques, Agroecosystem, Smart Public Spaces, Computer Vision, Image Processing, Open-Source",numberOfDownloads:null,numberOfWosCitations:0,numberOfCrossrefCitations:null,numberOfDimensionsCitations:null,numberOfTotalCitations:null,isAvailableForWebshopOrdering:!0,dateEndFirstStepPublish:"October 12th 2020",dateEndSecondStepPublish:"November 9th 2020",dateEndThirdStepPublish:"January 8th 2021",dateEndFourthStepPublish:"March 29th 2021",dateEndFifthStepPublish:"May 28th 2021",remainingDaysToSecondStep:"21 days",secondStepPassed:!0,currentStepOfPublishingProcess:3,editedByType:null,kuFlag:!1,biosketch:"Environmental technologist expert in the development of Smart Technologies for water management and environmental monitoring, characterization, and monitoring of contaminated and degraded sites, integration of spatial data such as standard methodologies, interoperability, spectral data infrastructures.",coeditorOneBiosketch:null,coeditorTwoBiosketch:null,coeditorThreeBiosketch:null,coeditorFourBiosketch:null,coeditorFiveBiosketch:null,editors:[{id:"315689",title:"Dr.",name:"Carmine",middleName:null,surname:"Massarelli",slug:"carmine-massarelli",fullName:"Carmine Massarelli",profilePictureURL:"https://mts.intechopen.com/storage/users/315689/images/system/315689.jpg",biography:"Main activities:\n-development of Smart Technologies for water management and environmental monitoring;\n-characterization and monitoring of contaminated and degraded sites;\n-implementation of early warning systems and impact assessment systems also from multitemporal monitoring;\n-integration of spatial data: methodologies, standards, interoperability, spatial data infrastructures;\n-use of open source IT systems for the processing, analysis, and integration of remote sensing data with airborne and satellite sensors for thematic purposes such as characterization, control, and analysis of the territory in support of environmental policies relating to contaminated sites;\n-evaluation of the contamination of environmental matrices with specific tests and chemical analyses;\n-installation of airborne sensors and definition of flight parameters for Earth observation, CASI-1500 hyperspectral and TABI-320 thermal sensors;\n-acquisition of spectral signatures of objects through Fieldspec portable spectroradiometer and creation of databases in SQL language;\n-use of tools such as Ground Penetrating Radar for the advanced investigation of the subsoil with law enforcement agencies.",institutionString:"National Research Council",position:null,outsideEditionCount:0,totalCites:0,totalAuthoredChapters:"0",totalChapterViews:"0",totalEditedBooks:"0",institution:{name:"National Research Council",institutionURL:null,country:{name:"Italy"}}}],coeditorOne:null,coeditorTwo:null,coeditorThree:null,coeditorFour:null,coeditorFive:null,topics:[{id:"9",title:"Computer and Information Science",slug:"computer-and-information-science"}],chapters:null,productType:{id:"1",title:"Edited Volume",chapterContentType:"chapter",authoredCaption:"Edited by"},personalPublishingAssistant:{id:"270941",firstName:"Sandra",lastName:"Maljavac",middleName:null,title:"Ms.",imageUrl:"https://mts.intechopen.com/storage/users/270941/images/7824_n.jpg",email:"email@example.com",biography:"As an Author Service Manager my responsibilities include monitoring and facilitating all publishing activities for authors and editors. From chapter submission and review, to approval and revision, copyediting and design, until final publication, I work closely with authors and editors to ensure a simple and easy publishing process. I maintain constant and effective communication with authors, editors and reviewers, which allows for a level of personal support that enables contributors to fully commit and concentrate on the chapters they are writing, editing, or reviewing. I assist authors in the preparation of their full chapter submissions and track important deadlines and ensure they are met. I help to coordinate internal processes such as linguistic review, and monitor the technical aspects of the process. As an ASM I am also involved in the acquisition of editors. 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To understand a plasma state and its characteristics, numerous experimental techniques, mechanisms, devices, theoretical models, and computational packages have been developed as diagnostic tools for measuring the plasma parameters such as the plasma electron density and temperature [1, 2] as well as their spatial profiles and dynamics. These diagnostic techniques are used to adequately describe both low-temperature and high energy density plasmas. In some situations, the measurements by these techniques cause perturbations in plasmas and are termed as active diagnostic techniques, while passive ones do not perturb plasmas. Based on the degree of ionization, the plasmas can broadly be classified into cold and hot plasma states, which accordingly demand for various types of diagnostics to precisely estimate the plasma parameters for optimal understanding of the physics of plasmas. This includes both theoretical and experimental findings. The most common techniques for cold and hot plasmas (\n\n few keV) are the Langmuir probes in the form of planar, cylindrical, or spherical electrodes in plasmas with a goal to monitor the plasma parameters. The probes can be of several types, namely, single and/or double probes, which are used for density, temperature, and floating potential measurements. Emissive and magnetic probes work more efficiently for plasma potential measurement and wave field amplitude and phase diagnostics, respectively, while the Rogowski for antenna current measurements. There are many complications, for example, the plasma potential and density can fluctuate or drift during the time of probe measurements. In some complications, since the probe draws a large amount of currents from a plasma and perturbs the initial state of the plasma, it may lead to the erroneous measurements; even then, the Langmuir probe diagnostics are widely used and this is because of the fact that they are relatively simple to use, cheap, and give reliable values of important plasma parameters.\n
On the other hand, in certain plasma sources like tokamak plasmas, strong currents are generated, which give rise to various kinds of magnetohydrodynamic (MHD) instabilities. For this, a magnetic probe is used, which is beneficial especially for measuring either local magnetic fields or its fluctuations not only in tokamaks but also in laser-produced plasmas (LPP). Furthermore, the amplitude of current flowing into the plasma can be estimated by integrating the induced magnetic field around the plasma column by utilizing the so-called Rogowski coil. However, in some plasmas (especially high temperature), it is not feasible to utilize material probes for determining the plasma parameter like plasma electron density. Therefore, a nonperturbing approach is needed to diagnose the plasma. In such a scenario, the electromagnetic spectrum is utilized. But the electromagnetic wave intensity must be low enough to the level that it will not result in plasma perturbation. For probing the high-density plasmas, a lower wavelength is required as a probe. This justifies the utilization of infrared radiation in tokamak and ultraviolet radiation for measuring the plasma electron density in LPP. The variation of the polarizing angle involving the beam probe in the presence of magnetic field can also be used for diagnostics of tokamak plasmas.\n
Interestingly, the evaluation of appropriate plasma parameters may be carried out by spectroscopy of emitted radiations as used generally from the beginning of plasma physics. This technique for emission measurements has been particularly making significant contributions over the past five decades for the fact that plasmas produced for nuclear fusion research exhibit intense emission in the X-ray region. Astrophysical applications further justify the wide interest in X-ray emission from plasmas. The phase soft X-ray (so defined due to their low penetrating power) indicates electromagnetic radiations with a wavelength in range \n\n (or, in terms of photon energy \n\n, 300 eV\n\n keV). Hard X-rays below 1 Å are occasionally produced in plasmas for highly accelerated electrons, like runaway electrons in tokamak plasmas and suprathermal electrons in LPP [3]. The characteristics of soft X-ray spectra like line intensities, line profiles, and continuum intensities can be investigated to determine the electron densities by Stark broadening, while the ion densities from the absolute radiation intensities and ion temperatures using the Doppler broadening of spectral lines [2].\n
The particle measurement method is another scheme for investigating the characteristics of plasmas by using the beam of fast particles. It has received much attention in the studies of inertial confinement fusion and energy deposition in a medium driven by cluster-ion and fast heavy-ion beams, as well as in plasma accelerators and low-temperature laboratory plasmas.\n
The most common ingredient of astrospace plasmas is the dust component in addition to electrons and ions, found everywhere in earth atmospheres, in comets, in planetary rings, in interstellar clouds, in interplanetary space, in interstellar medium, etc. Dust grains may exist in the form of ice particles, metallic and dielectric materials, and are highly charged species due to different charging processes. For instance, the absorption of ambient electrons and ions on dust grain surface may lead to the negatively charged dust grains, while thermionic and secondary electron emissions as well as ultraviolet photoionization give rise to positively charged dust grains. Thus, a multispecies dusty plasma can be assumed as more complex plasma than conventional electron-ion plasma, for dust size, mass, and charge variations. Being an abundant component of the space and industrial plasmas [4, 5], dusty plasma has always attracted lots of interests for studying new distinct features of plasma modes [6, 7] with a static and dynamic background of dust grains both analytically and experimentally [8, 9, 10]. Numerous linear and nonlinear [viz., solitons, shocks, vortices, etc.] dusty modes and associated instabilities are investigated using the frameworks of perturbative and nonperturbative schemes.\n
The behavior of charged particles in plasmas can be described by the well-known fluid and kinetic theories [4, 11], essentially helpful for studying the basic properties of plasma waves and instabilities, depending strongly on the observed phenomena. Laboratory plasmas have effectively been modeled by fluid description, where charged fluids of plasma species are assumed in temporal and spatial configurations. But, it has been observed that fluid theory does not account for velocity space coordinate and is insufficient to study the wave phenomena in non-equilibrium plasmas, where particle distributions show significant deviations from the equilibrium states. Hence, fluid theory is unable to explain the wave-particle interactions that could lead to collisionless Landau damping phenomenon and many other interesting features of collective modes and instabilities. Conversely, kinetic theory adequately describes the physical phenomena in real time and phase space configurations, providing all information about plasma waves, instabilities, plasma equilibrium, Landau damping rate, etc.\n
Test charge techniques [12, 13] can be utilized to study the shielding of test charges in collisional [14] and turbulent [15] plasmas, the electric field [16], and far-field potential of a test charge in a nonuniform magnetoplasma [17], the wake-field excitations in charge fluctuating dusty plasmas [18], the two-body correlations [19], the energy loss of test charges [20], etc. If a test particle is projected into the plasma with a constant speed, its charge density is coupled with the plasma charge density by the space charge effects. Consequently, the test charge is screened by a cloud of opposite sign charges leading to the short-range Debye-Hückel (DH) potential. Of course, the speed of test charge significantly matters in plasmas when it is considered with respect to thermal speeds of plasma species. The interaction potentials and energy loss of charged particles have been recognized in many research areas, for example, in ion-cluster interaction with condensed matter [21, 22], in inertial confinement fusion [23, 24, 25], in particle acceleration [26], in low-temperature laboratory plasmas [27, 28], and in dense plasmas for heavy-ion energy deposition [29].\n
Montgomery et al. [13] employed the test charge technique to obtain far-field potential distribution around a test charge, which decays as the inverse cube of the distance from test charge in electron-ion Maxwellian plasmas. Subsequent investigations of shielded potentials have been phenomenally influenced by the ionic motion [30], electron-electron collisions [14, 31], and plasma turbulence [15]. The electrostatic potential [32] due to small and large test charge velocities has been investigated to display the excitation of long-range wakefields in Maxwellian plasmas. Shivamoggi and Mulser [33] examined the effects of magnetic field, collisions, and plasma inhomogeneity on the potential due to slowly and rapidly moving test charges [17, 34], and Lakshmi et al. [35] discussed the Debye shielding phenomenon in a dusty plasma by considering the Boltzmannian electrons and ions with cold negative dust grains. It was revealed that plasma parameters significantly alter the characteristics of small and large amplitude potentials. Later, Shukla [36] reported the FF potential for a slowly moving test charge in a Maxwellian dusty plasma and showed the impact of dust-charge variation on the dipole-like FF potential. Moreover, oscillatory wake-field can be excited behind the test charge [37] in a collisionless unmagnetized plasma with Maxwellian electrons and ions. Nambu et al. [38] extended this work to dusty plasmas and explained the resonant phenomenon of DA waves with a test charge, resulting in the long-range WF potential. Later, Shukla and Rao [39] analyzed the WF, DH, and FF potentials of test charge in a colloidal Maxwellian plasma accounting for the streaming ions and dust grains. It was found that external magnetic field and ion-streaming effects [40, 41] strongly affect the positive/negative potential regions in plasmas. To explore the effects of two-body correlations, dust-charge perturbations and dust-neutral collisions, various geometries have been designed for propagating test charges [18, 19, 20] in an unmagnetized Maxwellian dusty plasma. In all above investigations, the plasma particles are described by the Maxwellian distribution function.\n
The shielding phenomenon is one of the main objectives of this chapter to unfold many intrinsic properties of the Lorentzian space dusty plasma, which discerns it from the standard Maxwellian plasmas. It plays a key role in setting up the basic criteria for Lorentzian dusty plasmas. Any plasma medium can physically be polarized by the test charge to give rise to perfect screening if thermal agitations are absent in the plasma system. Conversely, an imperfect shielding occurs if the plasma particles get enough thermal energy to escape from the edge of screening cloud. The interaction potentials caused by the test charge are not only strongly influenced by different test charge speeds in comparison with the thermal speeds but also lead to the possibility of dust crystallization and dust coagulation in space Lorentzian dusty plasmas.\n
In some circumstances, the behavior of plasma particles cannot be described by the usual Maxwellian distribution function (df) but often modeled by the power-law df. When all or some of the plasma particles move faster than their thermal speeds, the plasma particles are known as superthermal/suprathermal species, showing high energy and velocity tails in the distribution. They are mostly accelerated by wave-particle interactions, modulational instabilities and Langmuir turbulence [42], beam-plasma interactions [43], solar wind where type III solar radio emissions occurs [44], intense microwave-plasma interactions [45], ionospheric heating experiments [46], etc. Recognizing the role of superthermal energetic particles in plasmas, the wave dynamics and instabilities need to be re-investigated with a power-law df that gives a better fit to empirical data from space plasmas. A 3D isotropic Kappa-df [47] for superthermal particles can be expressed as\n
The normalization constant and effective thermal speed are denoted by \n\n\n\n\n and \n\n respectively. The symbol \n\n indicates the Gamma function, and \n\n and \n\n are the velocity and equilibrium number density, whereas \n\n (ms\n) stands for the temperature (mass) of the \n\n species (\n\n for electrons and i for positive ions). The effective thermal speed \n\n is always realistic in the limit \n\n, where \n\n is the spectral index showing the deviation from the Maxwellian df. Figure 1 displays the normalized Kappa-df [as given by Eq. (1)] for the electrons as function of normalized electron speed with varying \n\n-index both in 2D and contour plots. See that superthermal electrons exhibit high energy tails at \n\n 4, and 10 in distribution curves, which tend to the Maxwell-Boltzmann distribution curve for \n\n Therefore superthermality effects are only significant for low values of Kappa, and for its infinite values, the Kappa-df exactly converges to the Maxwell-df \n\n It may be noted from contours (see Figure 1(b)) that light-colored regions correspond to more electrons at low speeds, and while moving toward the dense-colored regions, the number of electrons decreases but comparatively has high speeds. In 1968, for the first time, Vasyliunas [47] pointed out the implications of Kappa-df by fitting empirical data from solar wind and showed the significance of low values of electron spectral index, that is, \n\n The effects of high energy tails have significantly modified the dispersive properties of waves and instabilities [48, 49] in Lorentzian plasmas. Recently, Ali and Eliasson [50] investigated the impact of suprathermal hot electrons on the electrostatic potential of slowly moving test charge in a two-temperature electron plasma and extended the model for Lorentzian dusty plasmas [51].\n\n
To compute the potential distributions around a test charge, we consider a collisionless Lorentzian dusty plasma, containing the suprathermal electrons and ions with negatively charged dust grains following the Maxwell-df. The plasma is also assumed to be field-free in the sense that there is no external electric or magnetic field (viz., \n\n so that the equilibrium electrostatic potential \n\n The quasi-neutrality condition at equilibrium demands \n\n where \n\n being the equilibrium dust-charge state and \n\n denote the particle number densities of the jth species [j equals \n\n for Kappa-distributed electrons and ions while \n\n for negatively charged dust grains]. In this model, all the dust grains are assumed to be spherical in shape with constant size of radius \n\n and mass md\n.\n
The Lorentzian dusty plasma in the presence of a test charge can be described by the following linearized coupled set of Vlasov-Poisson equations:\n
where \n\n is the induced electric field with perturbed potential \n\n\n\n\n is the charge of the negative dust grains, and \n\n being the charge of electrons and positive ions. \n\n, \n\n, and \n\n identify the dust-charge density, electron-ion charge densities, and test charge density, respectively. The symbol \n\n stands for a 3D Dirac's delta function, and \n\n and \n\n are the Maxwell-df and Kappa-df with their perturbed parts \n\n and \n\n such that \n\n and \n\n. Also note that test particle has a charge \n\n which moves with a constant velocity \n\n along the z-axis in a Lorentzian dusty plasma.\n
Taking space–time Fourier analysis of Eqs. (2), (3), and (4), we obtain the Fourier transformed potential in this form\n
The modified longitudinal dielectric constant can be defined by\n
where \n\n being the angular frequency (wave number) and \n\n is the plasma oscillation frequency. It is important to mention that if Lorentzian dusty plasma does not contain any test charge, viz., \n\n, then Eq. (5) simply implies that \n\n showing a modified linear dispersion relation of electrostatic waves to account for superthermal electrons and ions. However, the inverse Fourier analysis of Eq. (5) leads to the standard form of electrostatic potential due to a test charge in a dusty plasma [11, 32].\n
The dielectric constant in terms of dielectric susceptibilities \n\n can be expressed as\n
where \n\n and \n\n are the Debye shielding lengths associated with the electron-ion effective speed \n\n and dust thermal speed \n\n The standard plasma dispersion functions for Kappa-distributed electrons and ions [48] and for Maxwellian dust grains [52], respectively, can be given by\n
with their corresponding arguments \n\n and \n\n\n\n
To proceed further, we shall consider two limiting cases of Eq. (8) by imposing certain limitations on the test charge speed in comparison with the thermal and acoustic speeds and simplify the interaction potentials [as given by Eq. (7)] in Lorentzian dusty plasmas.\n
For a slow test charge propagation in a Lorentzian dusty plasma, we assume that test charge speed \n\n is much slower than the dust thermal speed \n\n As a result, the test charge is shielded by all the plasma species, for example, electrons, ions, and dust grains. Since mass of the dust grains is larger than the mass of electrons and ions, therefore the dust thermal speed is much smaller than the electron and ion thermal speeds. Thus, imposing the inequalities \n\n, we consider only small argument expansions, that is, \n\n and \n\n, in the plasma dispersion functions to obtain a simplified expression for dielectric constant. The inverse of the latter eventually yields the following result\n
The modified effective Debye length \n\n can be simplified in this form\n
with superthermality parameters attributed to electrons and ions as\n
The usual Debye length in electron-ion plasma is denoted by \n\n with \n\n and \n\n representing the angle between the vectors \n\n and \n\n. For Maxwellian plasmas, the superthermality parameters \n\n as long as \n\n implying that the effective shielding length exactly coincides with the earlier result [35] for static cold dust grains. It may be noticed from Eq. (9) that the inverse of dielectric constant is significantly influenced by the dust Landau damping rate [13]. The importance of the latter was first pointed out [13] in 1968, and it was suggested that if a test charge moves slowly in comparison to the dust thermal speed, the dust Landau damping term appearing in Eq. (9) cannot be ignored. For a static test charge, we set \n\n and insert Eq. (9) into Eq. (7) to derive the short-range DH potential [53, 54] in the form \n\n where \n\n is the distance from the test charge to an observer in terms of radial and axial distances \n\n and \n\n respectively.\n
For numerical analyses, we can choose the data from the dusty plasma near Saturn's E ring, cited in Refs. [55, 56, 57, 58] and many references therein. The data essentially corresponds to the Radio and Plasma Wave Science (RPWS) instruments onboard the Cassini spacecraft, containing the plasma parameters, such as \n\n, \n\n\n\n\n, \n\n, \n\n, and \n\n The computation further helps us in finding the magnitude of the effective shielding length \n\n at the near-Maxwellian electrons and ions with \n\n. The impact of superthermal tails in the electron and ion distributions only appear at lower values of the Kappa that may result into the reduction of the shielding length \n\n for fixed \n\n and \n\n, as well as \n\n with \n\n and \n\n. Thus, we notice from Table 1 that for infinite values of the spectral indices, that is, \n\n the superthermality parameters \n\n tend to unity, implying that the effective shielding length exactly coincides with the previous results [35] for static cold dust grains. However, the variation due to superthermal electrons and ions is shown in three different combinations (see Table 1) to affect the normalized values of the effective Debye length and DH potential almost 4 digits beyond the decimal point. At lower Kappa-values, the impact is relatively enhanced and in turn, suprathermal ions more efficiently modify the effective shielding length and DH potential as compared to suprathermal electrons because the ions may take more time to attain the Maxwellian equilibrium due to their larger mass compared to electrons.\n
The effect of dust concentration [denoted through the parameter \n\n] is shown on the contours of normalized effective shielding length [as given by Eq. (10)] in Figure 2 for (a) \n\n and (b) \n\n as function of electron-to-ion temperature ratio in the range \n\n and electron spectral index \n\n at near-Maxwellian ions \n\n. Since the speed of the test charge is much lower than the dust thermal speed (viz., \n\n), the test charge is therefore screened by all the plasma species, viz., the electrons, ions, and dust grains, hence effectively modifying the shielding length. The effective shielding length is shown to be decreased in the dusty plasma in comparison with traditional electron-ion plasma and is strongly influenced by the suprathermal tails of electrons. The impact of the superthermal electrons at lower Kappa values is more effective in the case of electron-ion plasma than dusty plasma. In the plots, one can easily observe that light-colored regions correspond to higher values of the effective shielding length while dense-colored regions determine the lower values of the shielding length. However, in Figure 2(c) and (d), a reduction in the effective shielding length is revealed by the influence of suprathermal ions at near-Maxwellian electrons \n\n It may be noted that due to the variation of electron-to-ion temperature ratio against the ion spectral index, the magnitudes of effective shielding length become smaller at lower values of \n\n than the case of \n\n However, the effective shielding length approaches to the maximum value in the limit \n\n and decreases by enhancing the electron-to-ion temperature ratios.\n
To study short and long-range shielded potentials of a slowly moving test charge along the \n\n-axis in a Lorentzian dusty plasma, we use Eq. (9) into Eq. (7) and spherical polar coordinates, as \n\n\n\n\n, and \n\n to finally obtain the total potential \n\n as\n
The first part of Eq. (11) corresponds to the short-range Debye-Hückel (DH) potential, which accounts for the short distances between the test charge and observer, whereas the second part represents the long-range far-field potential in the limit \n\n decaying as the inverse cube of the distance to the test charge. Here \n\n is the distance from the test charge to observer with radial and axial positions \n\n and \n\n respectively. When \n\n, the effective Debye length \n\n approaches to \n\n with \n\n, and consequently Eq. (11) exactly coincides with the earlier result [36] in the limit \n\n, having null dust-charge fluctuations. In Figure 3, the magnitude of the effective shielding length varies against the specific ranges of the electron concentration \n\n and dust concentration \n\n for changing the (a) electron-to-ion temperature ratios \n\n at near-Maxwellian electrons and ions \n\n and (b) electron-to-dust temperature ratios \n\n with fixed \n\n for Kappa-distributed electrons and ions (i.e., \n\n), respectively. Note that for an electron-ion plasma, the effective shielding length is approached to unity [35] as the maximum value for isothermal case \n\n (black dotted curve) (see Figure 3(a)), which then decreases with respect to the electron concentration. For non-isothermal values, that is, \n\n (blue dashed curve), 4 (red solid curve), and 8 (black solid curve), the strength of the effective shielding however reduces in terms of fraction showing no more dominant impact of the electron concentration. In the presence of dust component, the effective shielding length is reduced as compared to the electron-ion plasma and clearly depends on the electron-to-dust temperature ratios \n\n at \n\n as can be seen in Figure 3(b).\n\n
The variation of the normalized DH potential \n\n caused by a slowly moving test charge is displayed against the normalized axial distance \n\n for varying the dust concentration \n\n\n\n\n and \n\n in Figure 4 for (a) non-Maxwellian electrons and ions, as well as (b) near-Maxwellian electrons and ions. The DH potentials fastly reduce with a variation of dust concentration and attain large magnitudes in the near-Maxwellian case at \n\n compared to non-Maxwellian case at \n\n\n\n\n
\nFigure 5 exhibits how suprathermal electrons and ions modify the profiles of long-range FF potential (\n\n caused by a slow test charge moving with speed \n\n. For small values of electron spectral index \n\n, the shielded FF potentials are more localized than the case at near-Maxwellian electrons for \n\n (see the red solid curve in Figure 5(a)). However, the magnitudes of the FF potential are comparatively decreased in Figure 5(b) because of the strong contribution of suprathermal ions.\n\n
To examine the resonant interaction of a test charge with DA waves, we first simply derive the dielectric constant of the DA waves using the limit \n\n in Eq. (8). We therefore consider the small and large argument expansions \n\n and \n\n of the plasma dispersion functions. On DA scales, the inertia is mainly provided by the negatively charged dust grains and restoring force by the pressures of superthermal inertialess electrons and ions for maintaining the propagation of DA waves. In typical laboratory plasmas, the frequency of DA waves is often below the dust plasma oscillation frequency in the range of 1–100 Hz. Thus, the modified dielectric constant for a Lorentzian dusty plasma takes the following form\n
The effective Debye length now gets a new form \n\n with \n\n. Note that dust-charge fluctuations are also ignored here because the characteristic damping rate attributed to dust charge fluctuations is much smaller than the collisional and Landau damping rates. The reciprocal of Eq. (12) can be simplified as\n
This is the DA resonance frequency with DA speed \n\n. For long wavelength limit \n\n, the DA frequency reduces to \n\n in the Lorentzian dusty plasma, while in the short wavelength limit \n\n the frequency simply approaches to the dust plasma oscillation frequency \n\n. The factor \n\n in Eq. (13) identifies the dynamical effects of dust grains, which may lead to an oscillatory WF potential strongly depending upon whether the product \n\n is smaller or larger than \n\n.\n
For static or slowly moving test charge in a Lorentzian dusty plasma, its potential distributions are found spherically symmetric both in the axial and radial directions. Consequently, the DH and FF shielded potentials are appropriately solved with spherical polar coordinates. However, if the test charge moves with finite speed in a specific direction along the z-axis, the resonant interaction of test charge with the DA wave leads to the asymmetric distribution of potential in the form of WF behind the test charge. The plasma model is then preferably solved in cylindrical coordinates. Thus, following the standard techniques [37, 38, 40] for DH and WF potentials, we make use of Eq. (13) into Eq. (7) to finally arrive at\n
where \n\n is the axial distance between the test charge and observer. The first part on the right hand side of Eq. (15) shows the contribution of modified DH potential and the second part corresponds to oscillatory WF potential accounting for the suprathermal electrons and ions in a Lorentzian dusty plasma. For \n\n and \n\n the WF potential becomes attractive [40] and dominates over the repulsive DH potential because the latter decreases rapidly beyond the shielding cloud. An oscillatory WF potential \n\n of a test charge moving with speed \n\n is shown along the axial direction \n\n as a function of spectral indices \n\n and \n\n in Figure 6(a) and (b), respectively. Observe that the amplitude of the WF potential increases as the superthermal indices \n\n and \n\n increase at fixed \n\n and \n\n. Moreover, the wakefield damps behind the test charge a bit earlier as shown in Figure 6(b) due to the strong dependence of suprathermal ions on the effective shielding length in comparison with the suprathermal electrons. The impact of electron-to-ion temperature ratio is also examined on the profiles of WF and DH potentials as a function of axial distance \n\n with fixed radial distance \n\n and \n\n as can be seen in Figure 7(a) and (b), respectively. It is important to examine that electron-to-ion temperature ratio suppresses the magnitudes of the WF and DH potentials at low values of \n\n in the Lorentzian dusty plasma (Figures 6 and 7).\n\n\n\n
In this case, the test charge is assumed to be moving much faster than all the plasma species (viz., the electrons, ions and negatively charged dust grains). Consequently, Eq. (6) can be expressed in 1D form to finally arrive at \n\n in the limits \n\n and \n\n. Thus, the test charge potential (7) simply leads to the Coulomb potential\n
It is now clear that if the test charge is moving very fast, then there is no shielding around it in the Lorentzian dusty plasma.\n
To conclude, we have briefly discussed different plasma diagnostic techniques and specifically investigated the novel features of interaction potentials caused by a test charge moving with constant velocity \n\n along the z-axis in a collisionless unmagnetized Lorentzian dusty plasma. For this purpose, the linearized coupled Vlasov-Poisson equations are employed to model suprathermal electrons and ions with Kappa-df, as well as negatively charged dust grains with Maxwell-df, respectively. After applying the space-time Fourier transformations, an electrostatic potential is obtained with a modified dielectric constant. For taking the test charge speed much smaller than the dust thermal speed in a Lorentzian dusty plasma, we then express the total potential distribution in terms of short-range Debye-Hückel (DH) and long-range far-field potentials. The DH potential exponentially decays with distance, whereas FF potential decreases as the inverse cube of the distance. Both the potentials are substantially influenced by the plasma and superthermality parameters. However, a resonating test charge with DA oscillations introduces the long-range WF potential excitations behind the test charge in Lorentzian dusty plasmas. A Coulomb potential is obtained when the test charge is moving very fast compared to plasma species, and there is no shielding around it in the Lorentzian dusty plasma.\n
Vladimirov and Nambu [40] have already utilized the idea of WF potential for making new materials by attracting the same polarity dust grains in dusty plasmas. The physics of attractive forces between the negatively charged dust grains is completely analogous to that of Cooper pairing of electrons in superconductors [59]. The dust particle physically polarizes the plasma medium and creates attractive potential regions, where positive ions from collective interaction of DA waves can be focused. This may in turn lead to the possibility for dust crystallization and dust coagulation in both laboratory and space dusty plasmas.\n
Dr. S. Ali dedicates this document to Late Prof. P.K. Shukla and Dr. B. Eliasson (University of Strathclyde, UK) who were very kind to him at many occasions during discussions on dusty plasmas, and acknowledges the partial financial assistance from USTC, Hefei, China, and ICTP, Trieste, Italy, for making his visits feasible in 2018 and 2019, respectively. Professor Y. Al-Hadeethi also acknowledges the technical support of the Deanship of Scientific Research (DSR), King Abdulaziz University, Saudi Arabia.\n
Energy and environmental problems such as pollution and global warming are the most outstanding challenges that humanity will face in the next 50 years. Lately, global energy demand primarily for conventional energy resources such as fossil fuel, coal and natural gas has been increasing with population growth and industrial development. Up till now, over 80% of energy consumption is met with from fossil fuels, which cause global warming and environmental pollution issues. Moreover, they are non-renewable and will ultimately be exhausted in the future. Due to the increasing interest in renewable energy sources, imminent research is being focused towards harvesting energy from natural resources. Among the various choices, exploitation of sunlight for energy production and environmental remediation is the utmost crucial research areas of the twenty-first century.\n
The ultimate renewable source of energy is the sun. Sunlight is the most abundant energy source available to mankind. The sun emits a large amount of energy (approximately 32 × 1024 joules/year), which is much more than the world's whole demand. It is abundantly available, and only its 0.01% use would meet the worldwide energy necessities [1]. In this context, photovoltaic (PV) technology is considered as one of the ideal candidates, as they convert solar energy directly into electricity. Hence, effectively converting solar energy directly into electricity has been a promising solution to the energy issues [2]. From the perspective of environmental protection and energy conservation, it is required to produce electricity from solar energy by means of photovoltaic devices or solar cells.\n
Solar cells are probably the foremost contributor to fulfill the future energy requirements. Several approaches have been made for the fabrication of solar cells. Generally, solar cells are classified as first-, second- and third-generation solar cells. The first-generation (1G) solar cells are also called conventional, traditional or wafer-based cells and include silicon solar cells (polysilicon and monocrystalline) [3]. The power conversion efficiencies (PCE) of crystalline silicon solar cells have reached up to 26.6%. The SSCs with more than 90% share are presently leading the commercial photovoltaic markets. However, they are characterized by a severe preparation conditions and high cost [4, 5]. The second-generation (2G) solar cells, thin-film solar cells which include direct band gap semiconductors, were then explored. These included cadmium telluride (CdTe), gallium arsenide (GaAs), copper zinc tin sulphide (CZTS) and copper indium gallium selenide (CIGS) thin-film solar cells [4]. Though thin-film solar cells have led to reduced cost as compared to silicon solar cell, they require high-temperature and vacuum vapor deposition processes. Furthermore, they mostly contain toxic and rare elements, thus limiting their widespread applications [6, 7]. To overcome these challenges, third-generation (3G) solution-processed solar cells have been developed, which include organic solar cells (OSCs), quantum dot-sensitized solar cells (QDSCs), dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) [8]. Several PV technologies are under continuous development to meet the world demand for energy; in this chapter, however, we will focus our discussion in the emerging PV devices, i.e. dye-sensitized solar cells and perovskite solar cells.\n
The solar cell performance can be measured by its power conversion efficiency (PCE), cost and stability. Solar cell efficiency is the "measure of its output power per unit intensity of the incident light". The basic measurement to control solar cell efficiency is current (I) and potential (V) measured over an external resistance and at incident light intensity. The I-V characteristics can be produced using a Keithley SourceMeter SMU instrument. The I-V measurements were carried out to get significant knowledge about parameters of the solar cell for cell's performance. The typical illumination condition used for measurement of solar cell is 100 mW.cm−2 (intensity of incident light), which is recognized as one sun or air mass (AM) 1.5. It is the sunlight that reaches the earth's surface through air mass at 42.8° angle. In laboratories, a solar simulator attains this standard illumination condition [9]. The photovoltaic parameters thus calculated are open-circuit voltage (VOC), short circuit current (ISC), fill factor (FF) and power conversion efficiency. In 2016, the power conversion efficiency values certified by the National Renewable Energy Laboratory (NREL), the best research dye-sensitized solar cell, organic photovoltaic cell (OPV) and the perovskite solar cell, are 11.9, 11.5 and 22.1%, respectively [10].\n
Exploring innovative materials with tailored nanostructures and desired properties for energy application is a recent research area. To this end, graphene has distinguishing advantages over conventional nanomaterials, and substantial efforts have been made to utilize its valuable features for efficient energy devices. Carbon nanomaterials such as graphene and CNTs due to their abundance, low cost, good electrical conductivity and high chemical stability have been applied in 3G solar cells [11, 12].\n
Graphene is a single thick sheet of sp2-hybridized carbon atoms organized in a hexagonal lattice [13]. Graphene, first discovered in 2004, has appeared as a rising star in material engineering. Geim and Novoselov winner of Nobel Prize in 2010 opened infinite new possibilities for graphene, and recently, around the world many efforts have been made to present graphene-related materials to many industries [14]. Graphene has extraordinary properties such as high electrical conductivity (108 S/m), good thermal conductivity (5000 W/mK), high surface area (2630 m2 g−1) and electron mobility (250,000 cm2/VS), excellent mechanical strength, room temperature quantum hall effect, tunable band gap and good biocompatibility [15, 16]. Graphene is extremely optically transparent material having absorption (<2.3%), transmittance (over 97.7%) and insignificant reflectance (<0.1%) [11].\n
Due to these interesting properties, graphene, GO and rGO have attracted increased popularity for the use in optoelectronic (LEDs, photodetectors, touch screens, etc.), energy conversion (photocatalytic water splitting, photoelectrochemical (PEC) water splitting and photovoltaic cells), energy storage devices (batteries and capacitors) and environmental applications (gas sensors, photocatalytic degradation of pollutants and heavy metal removal) [17, 18, 19].\n
Geim and coworkers first isolated a 2D single layer of graphene from graphite by peel-off method in 2004 at Manchester University, named as Scotch tape method [20]. This led to an explosion of interest, and several studies have been carried out on the structure and properties of GO. Therefore, a series of approaches have been used to obtain a high-quality and large surface area graphene oxide. These approaches are classified into two main types: the bottom-up and the top-down.\n
The bottom-up approach is simple and is exfoliation of a graphene layer from a graphite. However, it requires high temperature and produces graphene with comparatively more defects than the top-down approach. Chemical vapor deposition (CVD), epitaxial growth on single-crystal SiC and carbonization are the representative bottom-up methods. CVD is a distinctive method used to synthesize large-area graphene sheets on metal foil substrates [20, 21, 22]. However, due to complexity, high temperature and cost of metal substrates, these methods are not widely used [22].\n
The top-down method involves the formation of graphene oxide using carbon-based materials. The top-down method has advantages like high yield, ease of operation and solution-based processability [12, 23]. This approach involves the chemical exfoliation of graphite, thermal exfoliation, electrochemical exfoliation and chemical reduction strategy. The typical method used for synthesis of GO was developed by Hummer and coworkers, which involves oxidation of graphite by sulfuric acid and potassium permanganate [18, 20].\n
Graphene oxide (GO) is the important derivative of graphene, which can be synthesized directly from graphite oxide. GO comprises of a 2D network of sp2- and sp3-bonded C atoms. The exceptional atomic and electronic structure of GO opens opportunities for new functionalities. GO is a highly oxidized graphene sheet containing many oxygen-comprising functional groups like carboxylic acid, hydroxyl, epoxide and carbonyl groups. Due to the presence of these oxygen-containing functional groups, graphene oxide is easily dispersible in water and other organic solvents [16, 23]. These functional groups are outstanding reactive sites for various functionalization reactions, nucleation and growth of nanoparticles [24]. Reduced graphene oxide (rGO) is an intermediate phase of GO and graphene, possessing various oxygen-containing functional groups and lattice surface defects which cause the electrocatalytic site in metal nanoparticles. Therefore, rGO exhibited better performance than the fully reduced defect-free graphene [12].\n
GO acts as semiconductor having band gap of 1.7 eV at room temperature. GO is an ambipolar material because it can act both as n- and p-type conductors. Therefore, they can be used both as ETL and HTL, depending upon the oxygen-containing functional groups in their structure. Graphene oxide, due to its unique structure and properties, has shown many advantages over rare metals, fluorine-doped tin oxide (FTO) and indium tin oxide (ITO) in optoelectronics such as solar cells and light-emitting diodes as shown in Figure 1 [12, 15, 25].\n\n
Graphene oxide tends to agglomerate because of van der Waals interaction between the graphene layers, preventing its application in several fields, though this drawback can be avoided by hybridizing graphene with CNTs, metal oxides and polymers [11]. To further explore the potential application of graphene-based materials, graphene nanocomposites are attracting more and more interest (Figure 2).\n\n
Graphene nanocomposites are emerging as a class of exciting materials that hold promise for many applications. Generally, graphene-based composites are formed by incorporating polymer, ceramics or metal nanoparticles into graphene. The incorporation of such materials into graphene is very desirable for tuning the morphology of surface, electronic structure, and fundamental properties of graphene. The enhanced properties of the GO-based composites are because of excellent physical and chemical properties of GO and incorporated nanoparticles [26].\n
The functional groups of GO such as the epoxide, hydroxyl, carbonyl and carboxyl group offer the attaching points for nanoparticles. The larger surface areas and the conductive graphene structure facilitate the charge transfer and redox reaction and enforce the mechanical strengths of composites. Although graphene sheets naturally stack into multilayers and hence their high surface area and essential physical and chemical properties are lost, however, when nanoparticles are incorporated into it, graphene sheets can assist as support materials to anchor them and improve the properties of GO [24].\n
GO-based nanocomposites are the research hotspots nowadays due to their large-scale production and synergistically enhanced effect. Considerable efforts have recently been reported for decorating graphene with metal oxide nanoparticles. To date, several kinds of metal oxides such as TiO2, ZnO, SnO2, MnO2, Co3O4, Fe3O3, Fe2O3, NiO and Cu2O have been incorporated into GO [16, 27]. Nanoparticle growth on graphene sheets is a significant approach to produce nanocomposites or nanohybrids, as controlled nucleation and growth offer optimal chemical interactions and bonding between graphene sheets and nanoparticles, leading to very strong electrical and mechanical coupling within the nanocomposite. GO-metal oxide nanocomposites have been found as promising materials for lithium batteries, sensors, solar cells, fuel cells, photocatalysis and organic synthesis [16, 17, 24].\n
Recently, graphene and graphene-based nanocomposite have been extensively explored in emerging 3G solar cells particularly in DSSCs and PSCs. Graphene and its derivatives have been widely used as transparent conducting electrodes, electron donor or acceptor materials and counter electrodes, playing a substantial role in increasing charge transport, reducing charge recombination and thus enhancing the performance of solar cell.\n
A dye-sensitized solar cell (DSSC or DYSC) is a low-cost solar cell, invented by Swiss scientists Michael Grätzel and Dr. Brian O'Regan in 1991, and is often called as Gräetzel cell (G Cell) [3]. DSSCs have attracted significant attention in search of substitute for silicon and thin-film solar cells due to their environmental friendliness, low fabrication costs and simple preparation process and remarkable conversion of solar energy into electricity [28]. DSSC is a photoelectrochemical system consisting of (a) transparent conducting working electrode (photoanode), (b) a dye sensitizer, (c) a counter electrode (cathode) and (d) an electrolyte [28, 29]. Its principle of operation is likened to natural photosynthesis process in plants. A monolayer of dye sensitizer absorbs incident light (like chlorophyll) giving rise to positive and negative carriers in the cell. On illumination, the electrons of the dye are excited from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). Then they are transported to the semiconductor's (TiO2) conduction band (CB) and diffuse through the semiconductor, being collected at the transparent conducting oxide (TCO). An electrolyte solution which typically comprises of an iodide/triiodide (I−/I3\n−) redox couple provides electrons to regenerate the oxidized dye. Eventually, the electrons transfer to the counter electrode (Pt) through the external circuit and reduces triiodide I3\n− ions back to the iodide I− to complete the circle of conversion of photons into electricity (Figure 3) [12, 30, 31].\n\n
The photoanode is a key constituent, as it strongly influences the photovoltage (V), the fill factor (FF) and the incident photon-to-current conversion efficiency (IPCE) [12]. It serves as the main energy conversion center, converting photons into electrical energy, thus playing a critical role in DSSC [25]. A good photoelectrode is assumed to provide good usage of light, good electron injection and good electron collection. Various semiconducting (wide band gap) materials such as TiO2, ZnO, SnO2, CdS and Nb2O5 have been successfully used as photoanode in DSSCs [28, 32]. Among all, TiO2 is most abundantly used, as it is nontoxic, cheap, chemically inert and easy to synthesize [33]. Moreover, TiO2 have a wide band gap 3.2 eV; predominant chemical, electrical and optical properties; low recombination rate for the hole-electron pair; and great absorption property [12, 28]. The performance of DSSC is significantly influenced by properties like particle size, porosity and thickness of TiO2 film.\n
Platinum (Pt) is the most widely used counter electrode (CE) in DSSC. Though Pt is very active to catalyze the reduction of triiodide, there are issues of stability in corrosive electrolytes and its high cost. Several efforts have been made to substitute it with less-expensive materials such as carbon materials and conducting polymers [34]. Carbon-based materials, such as graphite, carbon nanotubes, carbon black, nanocarbon and more recently graphene have been discovered severely as an alternative electrocatalyst for DSSC [17, 31].\n
Due to the exceptional mechanical, electrical and optical properties, graphene or highly reduced graphene are more appropriate as transparent electrodes, part of electrolyte, a light-harvesting dye and a counter electrode [17]. Additionally, work functions of graphene and rGO are calculated to be 4.4–4.5 eV, which are close to fluorine-doped tin oxide (FTO 4.4 eV) [25]. Thus, the tunable band gap of GO and its photon absorption ability in the visible and IR region permit to be a potential sensitizing material. The first application of graphene in DSSC as transparent conducting substrate was reported by Wang et al. [35] in 2008. They fabricated GO films by thermal reduction in Ar and/or H2 flux from exfoliated graphite oxide. These films showed a transparency of more than 70% and a higher conductivity of 550 S/cm [35]. Subsequently, other roles of GO have been widely explored in DSSC.\n
Among the extensively used semiconductors, TiO2 possess the longest diffusion length and lowest charge effective mass, but electron-hole recombination remains a significant issue [30]. Hence in order to reduce electron recombination and improve the stability of DSSC, graphene and graphene-based materials as photoanode have received great interest since the past few years.\n
The idea of using graphene into the photoanode of DSSC arises from the pioneering work of carbon nanotubes mixed with oxide nanostructures by Jang et al. [36]. This led to open an interesting field for researchers, quickly extended to graphene and its derivatives. The fascinating properties of graphene such as high transparency and Young's modulus make it a good candidate for transparent conducting substrates. The semimetallic properties and ultra-fast electron mobility allow graphene to serve as a charge carrier and as a transporter inside the semiconductor oxide layer in photoanode.\n
Kazmi et al. [31] used graphene-TiO2 nanocomposites as photoanode for DSSCs. They synthesized Gr-TiO2 with different graphene concentrations. Graphene nanoparticles were synthesized by modified Hummer's method, whereas TiO2 nanoparticles were purchased from Sigma Aldrich. The band gap was found to be reduced from 3.16 eV to 2.2 eV with the increase in GO concentration. Furthermore, conductivity increases with graphene concentration which supports well with the reduction in band gap. PCE of DSSC was enhanced with the addition of graphene, and optimum results were found for 3.0 wt% of graphene concentration.\n
Nouri et al. [30] have reported nanocomposite photoanode titania photoanodes with reduced graphene oxide rGO for DSSCs. They carried out comparative study on two ex situ and one in situ doping of TiO2 with rGO. The structural, optical and electrical characterization of the TiO2/RGO nanocomposites and the PV performance of the DSSC were studied by several techniques. UV-vis spectroscopy showed that the existence of rGO resulted in narrowing of band gap and visible light absorption, particularly in solvothermal in situ TiO2/RGO, representing chemical bonding between graphene sheets and TiO2 nanoparticles. This chemical bonding has been verified by XPS and Raman spectroscopy. In situ doping of TiO2 with RGO had the greatest beneficial effects on the performance of DSSC devices, yielding the highest Voc, Jsc, η and IPCE values. This was primarily ascribed to the role of RGO into the TiO2 films to facilitate electron transport and decrease electron-hole recombination.\n
Kanta et al. [10] carried out comparative study of the promoting effects of graphene in TiO2 photoanodes. They investigated the effect of the types and concentration of rGO on structural and photovoltaic properties of TiO2-based electrodes. GO was synthesized by modified Hummer's method. The synthesis of rGO was carried out by using two different methods: chemical reduction with vitamin C and thermal reduction. The thermal reduction method was conducted in situ during the fabrication and heat treatment processes of the DSSCs. It was observed that DSSCs containing GO/TiO2 photoanode (rGO by in situ thermal reduction) showed greater photovoltaic performance than rGO/TiO2. It was also found that the PCE of the DSSCs changed with the concentration of graphene in a nonlinear manner. The 0.01 wt% GO/TiO2 showed highest PCE (3.69%) values whereas for rGO based DSSCs 0.03 wt% rGO/TiO2 showed maximum PCE (2.90%).\n
Xu et al. [22] synthesized TiO2-RGO nanocomposites via an ultrasonication-assisted reduction method using GO in the TiO2 precursor solution. The reduction of GO and the formation of TiO2 crystals were carried out simultaneously. TiO2-RGO was characterized by SEM-EDX, FTIR, XRD, Raman, XPS, UV-vis and electrochemical impedance spectroscopy. By the introduction of RGO, absorption of light of octahedral TiO2 was markedly improved. In the meantime, the PCE of DSSC containing TiO2-RGO photoanode was also found to be highly improved.\n
Jamil et al. [28] fabricated DSSCs using G-Nb2O5 photoanode. Nb2O5 due to higher conduction band edge and open-circuit voltage is attracting attention. In order to reduce charge recombination and improve charge collection efficiency, an electrically conductive carbon material such as graphene was carried out. The performance of material and DSSC was characterized using X-ray diffraction, SEM, FTIR, diffuse reflectance UV-Vis spectroscopy and potentiostat. Studies showed that the incorporation of graphene enhanced the absorption and decreased the band gap resulting in an increase in the electrical conductivity and decrease in charge recombination rate. Moreover, IV measurements of the G-Nb2O5 cells showed the 68% increase in fill factor and 52% increase in efficiency (PCE) as compared to cells using Nb2O5 nanoparticles as a photoanode.\n
Effendi et al. [37] fabricated a Gr-ZnO nanocomposite photoanode for DSSCs by electrodeposition process. The DSSCs based on Gr-ZnO nanocomposite were studied through electrochemical impedance spectroscopy (EIS), UV-Visible diffused reflectance spectroscopy (UV-Vis) and photovoltaic performances J-V curves. EIS showed that a lesser charge transport time constant arisen in DSSCs based on Gr-ZnO nanocomposite as compared to ZnO. This enhanced the electron collection efficiency, resulting in high open-circuit voltage. Moreover, Gr-ZnO nanocomposite showed an effective photo-induced charge separation and transportation, thus exhibiting maximum photocurrent response as compared to ZnO. Moreover, The J-V curves demonstrated that incorporating graphene into the ZnO photoanode can permit the DSSC devices operate more efficiently. Gr-ZnO nanocomposite showed a maximum power conversion efficiency of 7.01%, which is doubled from pure ZnO photoanode.\n
Chou et al. [32] fabricated GO-TiO2 and zinc oxide nanowires (ZNWs) as photoelectrode layer of DSSC. The morphology and effects of ZNWs/GO-TiO2 were examined by the field emission scanning electron microscopy (FESEM), UV-visible spectrometer and solar simulator. The improvement of the photovoltaic performances of DSSC was due to the high specific surface area of GO and high electron mobility of ZnO. In addition, the electrochemical properties of GO-TiO2/ZNWs double structure were studied by electrochemical impedance spectroscopy. The high surface area of GO and the high electron mobility of ZnO could enhance the photovoltaic performances of DSSCs. Compared with the different composite films, the ZNWs/GO-TiO2 obviously showed higher dye loading. The optimal 3.82% PCE was achieved in DSSCs when the ZNWs/GO-TiO2 composite film was modified with 1.5 mL GO solution, which was 70.09% more than TiO2-based DSSC (3.82%).\n
Batmunkh et al. [38] used SnO2 and reduced SnO2-RGO as photoanode in DSSCs synthesized by microwave-assisted method. The incorporation of RGO into SnO2 resulted in greater electron transfer, thus enhancing the PCE of device by 91.5%. The improvement in efficiency can be ascribed to increase loading of dye, addition of suitable energy levels and enhanced electron transport of the photoanode (Table 1).\n
|VOC (V)\n
|JSC (mA/cm2)\n
|FF (%)\n
|PCE %\n
|FLG 1%-SnO2\n\n
|Ti at 1% GO\n
Bykkam et al. [39] used few-layered graphene (FLG)/SnO2 nanocomposite as a photoanode for DSSC. FLG varied from 1 to 3 wt %, and their effect was examined on the PCE. XRD patterns confirmed the existence of FLG and SnO2 nanoparticles in FLG/SnO2 nanocomposites. The band gap of SnO2 nanoparticles was found to be ~4.239, 4.237, 4.210 and 4.172 eV for FLG (1.0, 2.0 and 3.0 wt%)/SnO2 nanocomposites, respectively. An increased 3.02% PCE was observed for 1 wt% FLG/SnO2 nanocomposite as compared to pure SnO2 NPs. These results validated that suitable ratio of (1 wt%) FLG in SnO2 achieves the role of blocking layer to decrease the back electron-hole recombination in DSSC and thus enhance the PCE, though the higher wt% of the FLG causes shielding of the FLG resulting in decrease of efficiency of DSSC.\n
The discovery of organo metal halide perovskite CH3NH3PbX3 (X = halogen) as highly efficient light absorber in both photoelectrochemical and photovoltaic cells shed new light on emerging cheaper and highly efficient next-generation solution processed solar cells [7, 40]. Perovskite solar cells are a promising new substitute compared to silicon and dye-synthesized solar cells [2, 8]. PSCs have become the most promising photovoltaic technology, due to their high efficiency (certified 22.1%) and low cost in less than 8 years of development [4, 41, 42]. This extraordinary pace of development has gained much consideration and brought many engineers and scientists to this field.\n
Perovskite is named after the Russian scientist "Perovski" who first suggested the ABX3-type (e.g. CaTiO3) crystal structure for perovskites. For solar cell applications, a new class of perovskite material, organo metal trihalide, has been recently introduced. In organo metal trihalide perovskites, "A" is an "organic monovalent cation" (e.g. CH3NH3\n+), "B" is a "metal divalent cation" (e.g. Sn2+ or Pb2+) and "X" is a "halide anion" (e.g. Cl−, Br− or I−) [5, 41, 43].\n
Perovskite materials have exceptional properties such as a suitable band gap, high carrier mobility, broadband absorption of light, long carrier diffusion lengths and ambipolar transport due to which they have been explored as charge-transporting and light-absorbing materials in photovoltaic devices [41, 43]. A big advantage of PSCs is that they can react with light of various wavelengths, converting more sunlight into electricity and resulting in high efficiency. Furthermore, they are lightweight, flexible and semi-transparent. The first perovskite-based dye-sensitized solar cell CH3NH3PbBr3/TiO2 was developed in 2009 which obtained PCE of 3.13%, since then the PSCs have made an outstanding advancement, and in a period of 8 years, the PCE has been improved to around 23% (22.1% certified) [6, 44]. However, PSCs still face challenge of environmental and stability issues, which need to be improved.\n
Typically, PSCs with regular configuration (Figure 4) consists of three main layers:
Electron transport layer (ETL)
Perovskite absorber layer
Hole-transport layer (HTL)
The foremost function of an ETL is the extraction of photo-generated electrons from perovskite and their transference to electrodes. ETL also acts as hole-blocking layer (HBL) [45]. The basic prerequisite for an ideal ETL is high conductivity, excellent electron mobility, high optical transmittance and an appropriate work function [8, 44, 46]. As far as PSCs are concerned, various ETLs such as TiO2, SnO2, Nb2O5, ZnO, Zn2SO4, In2S3 and BaSnO3 have been used successfully using different techniques [46].\n
The HTL lies in the heart of solar cell in between the metal electrode and perovskite. It plays a vital role in the PSC structures and extracts positive charges (holes) from the perovskite and transports them to top electrode. It prevents the direct contact of Perovskite and top electrode [47]. The most widely used hole-transporting material is Spiro-OMeTAD. Other materials used as HTL are PEDOT:PSS, P3HT, PTAA, NiO, CuSCN, etc. [41, 47].\n
A PSC includes a perovskite (ABX3)-structured compound as the light-harvesting active layer, most commonly organic–inorganic lead halide-based material. The perovskites commonly used as active layer are methylammonium lead triiodide (CH3NH3PbI3) and formamidinium lead triiodide (CH3(NH2)2PbI3) [4, 48]. Perovskite has a cubic crystal (Figure 5) structure with three-dimensional (3D) framework and shares BX6 octahedron with the A ion placed at the octahedral interstices [4, 5, 47, 48]. The perovskite has unique ambipolar properties of generating and transporting both photo-generated holes and electrons. They act both as efficient light absorbers and charge carriers [47].\n\n
Theoretically, the working principle of photovoltaic devices involves four general processes as represented by Figure 6.
Absorption of light
Separation of charges
Transport of charge
Charge collection
Upon light illumination, the perovskite material undergoes photoexcitation and charge separation. The photoexcitation generates an electron-hole pair in the perovskite material. Then, diffusion of electrons and holes occurs toward the interfaces of perovskites/charge selective layers, respectively. After charge carrier (electrons and holes) extractions to charge selective layers, electrons and holes diffuse in the ETM and HTM, respectively, towards the corresponding electrodes for charge collection. These charge carriers produce a potential difference at the back and front contacts of the PSCs and can generate an electric current [4, 41].\n
In 2009, MAPbI3 was first used as sensitizer by Miyasaka and coworkers in liquid-state DSSCs with a PCE of 3.81% [49]. In 2011, a PCE of 6.5% was reported for perovskite-sensitized DSSCs in which perovskite quantum dots were used as sensitizers [50]. However, a foremost advancement was achieved in 2012, using organometal halide perovskite sensitizers in perovskite-based solid state DSSCs (or PSCs), and PCEs of 9.7 and 10.9% were obtained [4]. Later, more exciting discoveries and advancement on PSCs arose within a short period of time from 2012 to 2015, and a PCE of 22.1% was achieved [4].\n
Though the highest efficiency in solution-processable PSCs have been achieved using metal oxide electron transporting layer, those electrodes require sintering at higher temperature of 500°C, which is not economical and unfavorable for the fabrication of PSCs on plastic substrates. Furthermore, the charge carrier recombination at a metal oxide/perovskite interface is another critical factor in PSCs that delays the charge transportation and decreases the PCE of a device. To report this problem, the graphene and its derivatives and graphene/metal oxide nanocomposites have been as ETL [51]. Recently, some graphene/metal oxide nanocomposites such as G/ZnO, G/TiO2, G/SnO2, etc. have been used successfully as photoanode in PSCs.\n
Graphene nanocomposite with TiO2 as a low-cost, low-temperature solution processed collection layer in mesostructured PSCs was fabricated by Wang et al. [52]. Graphene nanoflakes provided greater charge collection in nanocomposites, allowing the fabrication of devices at lower temperatures (150°C). These devices showed extraordinary photovoltaic performance with maximum PCE up to 15.6%. Hence, G/TiO2 nanocomposites demonstrated its possibility to contribute significantly towards the progress of low-cost solar cells.\n
Han et al. [53], reported reduced graphene oxide/mesoporous (mp)-TiO2 nanocomposite-based mesostructured PSCs that demonstrated an improved electron transport property due to the reduced interfacial resistance. The amount of rGO added to the TiO2 nanoparticles was optimized, and their effects on electron diffusion, film resistivity, recombination time and photovoltaic performance were investigated. The rGO/mp-TiO2 film decreases interfacial resistance when compared to the mp-TiO2 film, and, thus, it improves charge collection efficiency. This effect significantly increases the VOC and ISC. The rGO/mp-TiO2 nanocomposite film with an optimal rGO 0.4 vol% content showed 18% higher PCE than the PSCs using TiO2 nanoparticles.\n
Saleem et al. [33] reported a new, low-temperature solution-processing approach to use rGO-TiO2 composite material for the electron transport layer of PSCs. GO was synthesized by a modified Hummer's method and TiO2 nanoparticles by hydrothermal method. Thin films of GO-TiO2 were made with different wt.% of GO on indium tin oxide (ITO) substrate by spin coating, followed by annealing at 150°C. The band gap of the pure TiO2 thin film was calculated to be 3.5 eV, which was reduced to 2.9 eV for the GO-TiO2 nanocomposites with a red shift towards higher wavelength. Moreover, thermal post annealing at 400°C enhanced the transparency in the visible region and decreased the sheet resistance. The I-V study indicated an ohmic contact with the ITO substrate.\n
Chandrasekhar and Komarala [51] fabricated PSCs using a graphene/ZnO nanocomposite (G/ZnO NC) as an electron-transporting layer. ZnO and G/ZnO NC films were developed by a novel spray deposition method compatible with large-area processing methods for deposition of pristine. The effect of amount of graphene concentration was studied, and GO amount varied from 0 to 1 wt% in the G/ZnO NC films. It was found that a 0.75 wt% GO concentration in the G/ZnO NC films gives the best PSC performance with ISC and PCE going up from 15.54 to 19.97 mA cm−2 and 7.01 to 10.34%, respectively, as compared to pristine ZnO. The improvement in PV performance is ascribed to the higher growth of the perovskite thin film and enhanced electron transport/extraction by using the graphene amount in the NC.\n
Xie et al. [54] improved the electronic properties of SnO2 by adding minute amount of graphene quantum dots (GQDs) and reported improvement in electronic properties of SnO2. The photo-generated electrons in GQDs can be easily transferred to the conduction band of SnO2, thus enhancing the conductivity of SnO2 and reducing the charge recombination at the interface. SnO2/GQDs fabricated solar cell showed low hysteresis and average PCE of 19.2%.\n
Xiaojuan et al. [55] tried to incorporate chemical modified (2D naphthalene diimide) graphene into SnO2 nanocrystal as ETL for highly efficient PSCs. They modified SnO2 with 2D naphthalene diimide-graphene, which can increase the surface hydrophobicity and is responsible for the van der Waals interactions between surfactant and perovskite. Thus, highly efficient PSCs were fabricated with maximum PCE of 20.2% and enhanced fill factor of 82%, which could be attributed to the improved electron extraction ability, electron mobility and the reduced carrier recombination, resulting in the increased FF. This work provides an important direction for further search in utilizing carbonaceous materials for low-temperature solution-processed planar PSCs (Table 2).\n
|Electron-transporting layer\n
|VOC (V)\n
|JSC (mA/Cm2)\n
|FF (%)\n
|PCE (%)\n
|TiO2 NP\n
|High-temperature-sintered TiO2\n\n
|SnO2-sintered free\n
|SnO2 nanobelts\n
|(0.4 vol %) rGO/mp-TiO2\n\n
|TiO2 + graphene\n
|0.75 wt% G/ZnO\n
Graphene, due to its unique properties, has been explored widely in solar cells, and graphene metal oxide nanocomposites have been widely used in emerging third-generation solar cells. In view of reported literature, it is obvious that these materials played a significant role in enhancing the efficiency of 3G solar cells. In this chapter, the use of graphene nanocomposites has been explored in DSSCs and PSCs. Graphene nanocomposites as photoanode material in DSSCs seemed to be a promising approach to increase the charge transport, charge separation and thus the performance of solar cell. The low cost of graphene brings new prospects for commercialization, particularly to replace the use of Pt as counter electrode in DSSCs. In PSCs, the use of graphene and its derivatives with metal oxide (G/metal oxide nanocomposites) as electron transport layer has shown to be valuable. Incorporating of graphene into metal oxide reduces the series resistance and the charge recombination between perovskite and metal oxide as well as improves the electron and hole transport from the perovskite layer to the corresponding electrodes. Moreover, graphene nanocomposites have proved to be an efficient electron-transporting layer fabricated at lower temperature, thus suitable for flexible substrates in PSCs. Furthermore, these materials are interesting to replace Pt-FTO or ITO and noble metals (silver or gold) in 3G solar cells. Thus, the efficient replacement of the existing expensive materials reduces the cost of third-generation solar cells.\n
Graphene-based materials are interesting from the perspective of both fundamental science and technology due to their nontoxicity, chemical and thermal stability and mechanical strength. Although graphene metal oxide nanocomposites can be used to enhance the PCE of 3G solar cells by various optimization methods, manufacturing of highly efficient and stable solar cell is challenging. Moreover, much practical work needs to be done to obtain the optimal performance. From the future perspective, a mechanism for physical-chemical interactions of these nanocomposites in different layers of solar cells is necessary.\n
From energy point of view, graphene metal oxide nanocomposites can be used for energy storage and conversion devices such as solar cells, fuel cells, batteries, capacitors, etc. The unique graphene properties, such as high conductivity and transparency, offer to replace the ITO, which lacks the flexibility and robustness in flexible solar cells, light-emitting diodes (LEDs), touch screens and displays. Graphene/metal oxide nanocomposites can be used to improve the durability of potential optoelectronic devices. Graphene/metal oxide nanocomposites are promising substitutes to decrease the drawbacks of using only metal oxide nanoparticles in various applications, such as anode materials in lithium ion batteries (LIBs), sensors, photocatalysts, removal of organic pollutants, etc. The graphene/metal oxide nanocomposites showed greater versatility as enhanced materials for the fabrication of electrochemical sensors and biosensors.\n
Graphene, due to its antibacterial, antiplatelet and anticancer activities, make it a potential candidate for biological and biomedical applications, and graphene/metal oxide nanocomposites can be used in cancer therapy, drug delivery, bioimaging, tissue engineering, etc. The synthesis, toxicity, biocompatibility and biomedical applications of graphene/metal oxide nanocomposites are important issues that require thorough investigation in any kind of applications related to human welfare.\n
Despite the substantial progress in the synthesis of graphene-based nanocomposites, challenges exist in the application on an industrial scale. For example, advanced applications of graphene/metal oxide nanocomposites require wide research to understand the interactions between graphene surface and the nanomaterials, which will have direct influence on the properties of these nanocomposites. An appropriate understanding of these interactions will surely enhance the application potential of the nanocomposites in various fields, such as catalysis, biosensing, drug delivery, imaging etc. Therefore, graphene metal oxide composites have vast potential for many industrial applications, and they are commercially feasible compared to carbonaceous-based nanocomposites.\n
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ViewSonic VX924 review
There's been a lot of talk about LCD response times over the past few years. Faster response times are better, at least in theory, as they should avoid the apparent problem with motion lag that's kept dedicated gamers and movie buffs clinging on to CRTs. ViewSonic's VX924 panel has the lowest quoted response time yet, at 4ms.
There are two issues with these figures, though. First, it takes longer for a black pixel to switch to a 'middle' state (such as a shade of grey) than it does to white, because the crystals move more slowly without maximum voltage applied. ViewSonic's solution to this is its ClearMotiv system, which initially applies a high voltage to kick-start the transition, reducing it as the crystals move, to even out response times across the spectrum.
The second issue is that even a 16ms response time can theoretically cope with 62.5 individual frames per second – well over that needed to produce full-motion video or decent gameplay, so it's clear that the quoted figure alone doesn't tell the full story.
And, in practice, the VX924 doesn't bring to an end the issue of TFT versus CRT. A fast-moving white box on a black background appears to have soft edges, as well as a slight shadow behind it. The same test on a decent CRT results in crisp edges with a distinct trailing tail. But don't let this cloud your buying decision: the VX924 is notably better at handling swift, high-contrast movement than the vast majority of TFTs that pass through our labs. When playing games or watching movies, it's an improvement you'll notice only rarely, but it's still welcome.
Thankfully, the rest of the panel's performance is outstanding. There are a few small blemishes – a slight lack of vibrancy and a minor loss of red saturation – but everything else is superb. The detail offered at the dark end of the scale near black was matched at the white end, and we could distinguish blocks just two steps (out of 256) away from pure black and white without much trouble. This brings out detail in shadows or flared highlights on still images, and clarifies shadows on films – and that's on the default settings. Contrast is well maintained with changes in viewing angles too, and there's practically no discolouration off-centre.
There's also attention to detail elsewhere, with an attractive (if chunky) 27mm bezel, and a stand with a clever system for taming messy cables. The OSD is clear and easy to use, offering contrast and brightness control even with the DVI-D digital input, while colour temperature options include sRGB. The only things you have to forego are swivel and height adjustment, with the stand allowing tilt only.
But in spite of some small compromises, this panel impresses all-round. The exceptional range, decent motion handling and excellent viewing angles mean the VX924 is a great choice for all but colour-critical purposes, and it's available at a reasonable price too.
Disclaimer: Some pages on this site may include an affiliate link. This does not effect our editorial in any way.


text:
2017 kitchens
Collection by Leesa Gant
Obsessed with this cafe doors on an upper oven! No more burned elbows! #DreamKitchen
Cabinets give off an old-world vibe
Cabinets give off an old-world vibe by helen on Indulgy.com
Like the corner unit with the microwave.
Zucchini Lasagna An easy zucchini lasagna casserole with ground meat, onions, and tomato sauce. Keto, low carb, and gluten free. ## ...
Warming Up Your Neutrals — Elements of Style Blog
Image by Michael J. Lee for Elements of Family Style. It's clear that for 2020 the go-to neutral is much warmer than what we've been seeing the past five years. I, for one, am delighted. I always find warm neutrals to feel much more livable and more expensive feeling than colder greys.…
I like the square light fixtures over the island and the low barstools. #kitchensettingideas
2016 In Review: Top 10 Favorite Posts + Projects
2016 In Review: Top 10 Favorite Posts + Projects. Today I'm revisiting a few of our 2016 highlights, our very favorite Simple Stylings posts and projects!
If you are reading my blog from the splendidsass.com address, please take note that I will soon be using that address for another purpose, s...
Gold and Brass Home Decor trending for 2018
Gold and Brass home decor trending for 2018. Whether your style is bohemian, minimal, traditional or farmhouse chic there's always room for a little gold!


text:
Warehouse General Helper
Company: Bluecrew
Location: Alta Loma
Posted on: November 12, 2020
Job Description:
$500 Sign-On Bonus
We are looking for a capable Warehouse General Helper to support our company's warehouse operations. You will receive, input, sort, load and unload products and you will perform other various warehouse activities.
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*New Crew Members include anyone who works their first shift on or after October 5, 2020. We reserve the right to withhold or deduct payments that we determine or believe were in error, fraudulent, illegal, or in violation of employee terms or these terms. This offer is available for a limited time only and is subject to availability. Terms are subject to change. Crew Members can earn either or both bonuses!
$500 Sign-On Bonus
Keywords: Bluecrew, Rancho Cucamonga , Warehouse General Helper, Professions , Alta Loma, California
here to apply!
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Demon Queens & Kings is interested in a small group to join us. We've lost a few long-time members over the holidays, but we are still very active and chugging along. We are currently hitting 9* Titans and been successful following an international war strategy.
We would like any group joining us to have a majority having level 38+ with a love for alliance war. Trophy count is negotiable but most of us are above 3800 TP. We will have 7 spots free after the current war. Feel free to scout us out directly or line me at junphilyan, thx


text: Scroll through this Makro catalogue valid from 11.01.2020 to 12.16.2020 to see the latest deals. On 2 pages of the currently valid catalogue, you will find the best goods from the Groceries category. This Makro catalogue offers discounts on more than 63 products, making sure you get the best deal on the things you buy! If you want to save on your next shopping trip to Makro, don't forget to look through the entire catalogue from page 1 to page 2. On the current page you will find promotions on beans, biscuits, corn, cream, custard, flour, mayonnaise; however, this brochure from Makro offers many other discounts on goods like colgate, margarine, mint, nestlé, new era. If you want to shop smart and save on your next shopping trip to Makro, don't miss the latest weekly catalogue full of amazing prices and wonderful discounts. Come back to My Catalogue every day to make sure you don't miss out on great promotions offered by your favourite retailers.