Extracting energetic disorder in organic solar cells using percolation models

Abstract

The energetic disorder $\sigma$ describes the energy state distribution in organic semiconducting materials. In organic solar cells (OSCs), energetic disorder is an important parameter for evaluating the charge transport behavior, and it is strongly correlated with the device performance. Thus far, a widely used approach for extracting energetic disorder values in OSCs is the Gaussian disorder model (GDM), in which the disorder values can be extracted by fitting the slope of $\text{ln}\mu \sim \frac{1}{T^2}$, where $\mu$ is the charge mobility and $T$ is the temperature. Herein, we demonstrate the potential of the percolation approach to evaluate the energetic disorder values in OSCs and compare them with the data obtained using the GDM approach. Two typical non-fullerene acceptor (NFA)-based bulk heterojunction (BHJ) films, with PTB7-Th:ITIC and PM6:Y6, were selected as the model systems. When the percolation models were adopted in the two BHJ films, the energetic disorder values extracted from the Grünewald/Thomas and Nenashev percolation models gave similar results for electron transport in the PTB7-Th:ITIC and PM6:Y6 BHJ films. This work successfully demonstrates the feasibility of microresistance analysis in BHJ systems and the application potential of the percolation model for extracting energetic disorders in OSCs.