Lifetime enhancement for multi-photon absorption in intermediate band   solar cells
  A semiconductor structure consisting of two coupled quantum wells embedded into the intrinsic region of a {\it p-i-n} junction is proposed to be implemented as an intermediate band solar cell with ratchet state. The localized conduction subband of the right-hand side quantum well is thought as the intermediated band, while the excited conduction subband of the right-hand side quantum well, coupled to right-rand side one, is thought to acts as the ratchet state. The photo-excited electron in the intermediate band can tunnel out the thin barrier separating the wells and accumulate into ratchet subband. This might raise the electron probability of being hit by a second photon and exiting out to the continuum, increasing solar cell current. Is presented a temporal rate model for describing the charge transport properties of the cell. Calculations are carried out by solving the time-dependent Schr\"odinger equation applying the time evolution operator within a pertinent choice of the non-commuting kinetic and potential operators. The efficiency in the generation of current is analyzed directly by studying the occupation of the subbands wells in the p-i-n junction, taking into account the injection and draining dynamic provided by the electrical contacts connected to the cell. As a result, the efficiency in the generation of current was found to be directly correlated to the relationship between optical generation and recombination rates regarding to the scattering to the ratchet state rate. This suggests that a good coupling between the intermediate band and the additional band is a key point to be analyzed when developing an efficient solar cell. 
Anibal Thiago Bezerra, and Nelson Studart
cond-mat.mes-hall