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Fast and slow charge trapping and transport in organic semicondutors

In this thesis charge transport and associated processes in organic semiconductors are investigated from various points of view to identify fundamental mechanisms limiting device performance. This will hopefully contribute to establish a more coherent picture for the charge transport and partially replace the patchwork of theories which are used nowadays. In the first study we developed a full organic photovoltaic cell (OPV) simulator. The fundamental processes have been implemented from light incoupling to charge extraction. We then studied the limiting processes for various steady state as well as transient simulations and compared the results with actual measurements. This shows that transient measurements are an important part to identify and distinguish concurrent processes. In the next study we investigated so called slow charge traps in organic fieldeffect transistor (OFET) which limit the device performance. Through careful comparison of several device stacks we have been able to identify a system where slow charge trapping occurs in the semiconductor and therefore eliminates charge trapping in the gate dielectric, which normally occurs in almost all OFET devices. The third study is then focused on a comparison of charge transport and trapping in a n-type material. Using various processing methods we have been able to produce OFETs with a wide range of crystallinity. This is an important step for understanding how order/disorder due to morphological differences influences the spectral density of trap states (trap DOS) and thus charge transport. The last study is a survey to summarize the trap DOS in state of the art OFETs. For this investigation we have compared publications from the last 25 years to have a coherent picture of charge traps for organic pas well as n-type devices. A comparison to their inorganic counterparts is done as well. We also show a very simple method to extract the density of trap states from transfer