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Electrical transport properties of poly (3-hexylthiophene) (P3HT) (6,6)-phenyl C61-butyric acid methyl ester (PCBM) solar cells, with and without encapsulation, have been investigated and analyzed using admittance spectroscopy and capacitance voltage measurements at different temperatures. The admittance spectroscopy clearly reveals two defect states with activation energies of 53 and 100 meV, and a concentration ten times higher in the unencapsulated sample. These defects seem to have a strong effect on the charge transport and the solar cell performance when they are present with a high concentration, since they lead to a decrease of the mobility and also the short-circuit current and the efficiency. The origin of these defects has been assigned to reaction of the blend with O2 which is also known to induce p-type doping in pure P3HT. In an attempt to understand the effect of these defects on the organic solar cell performance, modeling and simulation were carried out using the effective medium layer model and gave good agreement with the measurements results.

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Cu(In,Ga)Se2-based thin film solar cell devices exhibit metastable electrical behavior. This behavior is often ascribed to intrinsic defects that can change configuration accompanied by large lattice relaxations. We extended the thin film solar cell simulation software scaps to enable the simulation of the metastable behavior of this kind of defects. The statistics that are needed to describe metastable defects are discussed. The procedure that has been implemented is introduced, and special attention is paid to the convergence of the method for high defect densities. The model is demonstrated by simulating the effect of voltage induced metastabilities on the capacitance-voltage characteristics. Some of the features present in the measured apparent doping density profiles can be directly related to presence of metastable defects.

The voltage dependence of the derivative of the capacitance to (the logarithm of) the measurement frequency is investigated. Relations describing this dependence are derived for the influence of carrier freeze out, of a defect distribution, and of a back contact barrier. The validity of these relations is investigated with numerical simulations. Considering the extraction of the defect density from capacitance-frequency measurements, the extension of existing formulas to different bias voltages leads to an improved accuracy and the possibility to investigate spatial non-uniformities while preserving a direct link between the defect level energy and the apparent defect density. This is illustrated with voltage dependent admittance measurements of thin film Cu(In,Ga)Se 2-based solar cell devices. V