Optimization of local orientation and vertical phase separation by adding a volatilizable solid additive to the J51:N2200 blend to improve its photovoltaic performance

Abstract

All polymer solar cells (APSCs) have attracted considerable attention due to their unique advantages such as flexibility and mechanical stability. However, their poor charge mobility and difficulty in accurately optimizing phase separation structures have limited their performance improvement. Here, we achieved a multilength scale morphology control of the molecular local orientation and component distribution of the J51:N2200 blend by adding a volatilizable solid additive Bipy to the blend. Since Bipy was more compatible with J51 than N2200, J51 could be enriched on the bottom surface. During thermal annealing, with evaporation of Bipy across the thin thickness direction, Bipy has more chance to contact N2200. The repulsive force between Bipy and NDI2OD units of N2200 enhanced the chain planarity of N2200 and the connectivity between crystalline lamellae. This dual role of Bipy in J51:N2200 contributes to increases of the charge mobility and more balanced charge transfer simultaneously. Meanwhile, the rate of charge recombination decreases and charge extraction increases which result in an efficient PCE of 8.73%.