Efficient organic solar cells based on low-cost pentacyclic fused-ring small molecule acceptors with a fill factor over 80%

Abstract

Small molecule acceptor (SMA) materials with pentacyclic fused-ring backbone are considered promising candidates for balancing the low-cost and high photovoltaic performance in the commercialization of organic solar cells (OSCs). However, power conversion efficiencies (PCEs) are often constrained by suboptimal short-circuit current density and fill factor, primarily due to the blue-shifted absorption spectra and poor charge transport of pentacyclic fused-ring SMAs. These limitations can be addressed by introducing multiple donor–acceptor (D–A) interactions and optimizing the side-chains. Herein, we designed and synthesized two A-DA′D-A type pentacyclic fused-ring SMAs, BZ4F-ch1 and BZ4F-ch2, featuring cyclohexyl side-chains onto the benzotriazole and terminal thiophene, respectively. Unlike the hypsochromic absorption of BZ4F-ch1 in chloroform, the BZ4F-ch1 neat film displayed a red-shifted absorption compared to the BZ4F-ch2 film. Additionally, BZ4F-ch1 exhibited a higher crystallinity than BZ4F-ch2. Moreover, the PM6: BZ4F-ch1 blend showed a superior phase separation morphology, charge transport and extraction. As a result, the PM6: BZ4F-ch1-based OSCs achieved a prominent efficiency of 16.02% with a significantly improved J_SC of 23.09 mA cm⁻² and FF of 80.41%. Furthermore, BZ4F-ch1 provided a high PCE/material-only cost (MOC) value of 3.56, implying decent cost-effectiveness. This work highlights the potential of pentacyclic fused-ring SMAs for developing high-performance and low-cost OSCs.