Benzannulation of furan: a strategy for stable and high-performance furan-containing giant electron acceptor with efficiency exceeding 20%

Abstract

The use of furan as a building block for electron acceptors in organic solar cells has been limited by its instability, particularly its susceptibility to Diels–Alder cycloaddition with singlet oxygen. In this study, we address the degradation challenges historically associated with furan through a benzannulation strategy, in which one of furan's double bonds is incorporated into an aromatic sextet, rendering the benzenoid aromaticity energetically unfavorable to disrupt via Diels–Alder cycloaddition. We synthesized a benzotrifuran-centered giant electron acceptor (BQx-O) with three arms, alongside benzotrithiophene (BQx-S) and benzotrisselenophene (BQx-Se) analogues for comparison. Quantum chemical calculations indicate that the BQx-O maintains a near-planar structure, promoting enhanced π-conjugation and molecular packing compared to the more twisted thiophene and selenophene counterparts. As a result, BQx-O achieved an outstanding power conversion efficiency (PCE) of 18.62% in binary OSCs, outperforming BQx-S (14.89%) and BQx-Se (12.62%), and setting a new benchmark for all furan-containing and all giant electron acceptors. In optimized ternary OSCs, BQx-O further reached a remarkable PCE of 20.11%. Moreover, the planar conformation of BQx-O and its reduced diffusion coefficient contribute to superior morphological and operational stability. This study demonstrates benzannulation as a straightforward yet powerful strategy for designing high-performance, stable furan-containing acceptors, expanding possibilities for innovative electron acceptor designs.