Distributions and evolution of trap states in non-fullerene organic solar cells

Abstract

The photovoltaic performance of non-fullerene organic solar cells (OSCs) is essentially determined by the presence of charge traps. However, their exact distributions in OSCs have remained unclear. Here, we report the successful profiling of spatial and energetic distributions of trap states via the drive-level capacitance profiling (DLCP) method. Our DLCP results unveil that the trap densities at device interfaces are 1 to 2 orders of magnitude greater than those of the film interior, and improving film crystallinity helps reduce trap density. Furthermore, the DLCP method enables operando monitoring of trap evolution during OSC operation, which reveals that trap evolution is strongly correlated with film morphology stability. The OSCs with stable morphology show minimal changes in trap distributions and can operate for 500 h without significant efficiency loss. With this method, we establish the correlations between trap distributions/evolution and device efficiency/stability and provide insightful guidance toward more efficient and stable OSCs.