Field-Dependent Charge Collection Model for Thin Film Organic Photovoltaics

Abstract

In this study, we developed a unified charge collection model using optical cavity dependent charge carrier generation and non-uniform built-in electric field distribution within a bulk heterojunction photovoltaic device. The charge collection model relies on the experimental inputs related to the charge carrier dynamics such as mobilities of charge carriers, recombination lifetime, and junction width of charge carrier species. Optical cavity modes and field strength were calculated using the experimental variable angle ellipsometry analysis of individual components of the devices. In order to evaluate the model, ambient processed PCDTBT:PC71BM based conventional and inverted derive architectures were utilized to underline the effect of unintentional doping and distinct optical cavity modes. The simulated external quantum efficiency and short-circuit current density profiles from the model were compared to the experimental results with differing active layers thicknesses and device architectures. The proposed charge collection model presented a high degree of correlation with the experimental results and underlined its validity for further application on other types of organic photovoltaic devices.