Extraction of charge transfer states dissociation probability and localised states parameters for PTB7-Th:PC71BM photovoltaic cells: using experimental J-V curves

Abstract

The efficient separation of bounded electron–hole pairs (excitons) through charge transfer states (CTS) is a fundamental process in organic photovoltaic cells (OPVs). Introduction of CTS dissociation probability CTSdis factor in the generation rate equations is a simple and effective method to estimate the number of dissociated CTS. In the present study, for a specified recombination coefficient (k), first we obtained the values of CTSdis and subsequently determined the localized states parameters, i.e., electron/hole trap densities, tail slopes, and trap cross sections within the active layer (PTB7-Th:PC71BM). In order to extract these values, the experimental data of dark/light J-V curves and the density of charge carriers at the electrodes are fitted using the downhill simplex algorithm. An iterative approach is used to obtain the converged values. Furthermore, we explored the effect of compositional variation on CTSdis and obtained values are 80%, 89%, 71%, and 57% for weight ratios of 1:1, 1:1.5, 1:2, and 1:2.5 respectively. All calculations and simulations are performed using OghmaNano.