Optimizing the miscibility for enhanced photovoltaic performance of non-fused ring electron acceptors through side-chain engineering†

Abstract

Non-fused ring electron acceptors (NFREAs), notable for their simple and economical synthesis processes, play a pivotal role in the practical deployment of organic solar cells (OSCs). However, the power conversion efficiency (PCE) of NFREA based devices lags behind that of fused ring electron acceptors, because of the inferior charge transport and severe charge recombination in donor:NFREA blend films. In this study, we synthesized two novel NFREAs, A1C4-Cl and A1C6-Cl, featuring different alkyl side-chain lengths to optimize the miscibility between the donor and NFREAs for ideal morphology, taking into consideration that the morphology of donor:NFREA blend films has a significant influence on charge transport and recombination. The PBDB-T:A1C6-Cl based OSC exhibits better miscibility and more favourable phase separation, resulting in enhanced charge carrier mobilities and suppressed trap-assisted recombination. These improvements lead to a significant increase in short-circuit current density (J_SC) and fill factor (FF), culminating in a PCE of 12.11% compared to PBDB-T:A1C4-Cl based devices. Our findings offer an effective approach to modulate the miscibility between donors and NFREAs, thereby enhancing the PCE of OSCs through the fine-tuning of alkyl side-chain lengths.