Non-fused ring electron acceptors employing diphenylamine substituted 2,2′-bithiazole cores for organic solar cell applications

Abstract

Herein, we report the synthesis of three 2,2′-bithiazole based A–D–A′–D–A type non-fused ring electron acceptors (NFREAs) with different diphenylamine groups as the side-chain (Me-2F, C4-2F, and tBu–2F). These molecules achieve bandgaps of ca. 1.5 eV with the same conjugated backbone. However, the subtle side-chain variations significantly influence the optoelectronic properties of acceptors, the molecular orientation, and the final solar cell performance. As a result, the PM6:C4-2F based device achieves the best power conversion efficiency of 11.66% with a J_SC of 18.47 mA cm⁻², a V_oc of 0.912 V, and a FF of 69.2% among three NFREA devices due to the efficient charge transfer, less recombination, face-on orientation and more balanced charge transport. These results highlight that 2,2′-bithiazole with diphenylamine side groups is a promising building block to construct high-performance and low-cost A–D–A′–D–A type NFREAs, and alkyl chain engineering on the bulky side groups significantly influences the molecular orientation and solar cell performance.