Direct determination of defect density of states in organic bulk heterojunction solar cells

Abstract

The measurement of the occupied trap density of states (DOS) is important for optimization of organic bulk heterojunction solar cells. We demonstrate a direct method for obtaining it from the trap related peak in capacitance-voltage characteristics under different levels of illumination, and its correlation with the dark current density-voltage characteristics. We use the method to measure the parameters of DOS, occupied trap distribution, and its temperature dependence for poly(3-hexathiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) based solar cells. The total occupied trap concentration is approximately 7 × 1015 cm−3 with a standard deviation for a truncated Gaussian distribution varying between 32 and 44 meV in the temperature range of 310–270 K within a total Gaussian DOS with a standard deviation of 92 meV.