A Designed Ladder-Type Heteroarene Benzodi(Thienopyran) for High-Performance Fullerene-Free Organic Solar Cells

Abstract

To meet the imminent requirement of fullerene-free electron acceptors, a new ladder-type heteroarene benzodi(thienopyran) (BDTP) is designed and synthesized by embedding pyran rings in [2,2-(2,5-dialkyloxy-1,4-phenylene)dithiophene] (PDT) for organic photovoltaic (OPV) applications. Originating from the strong p-π conjugation of the oxygen atom in the pyran rings, electron-rich BDTP results in the BDTP-cored molecular acceptor, NBDTP, with strong intramolecular charge transfer effect. With sp3 carbons in pyran rings, NBDTP have the flexibility of targeted modification to resolve the solubility as well as the morphological tuning by handy alkyl chain attachment. As a result, the fusion of pyran rings in BDTP means that the acceptor exhibits a narrow optical band gap of 1.58 eV and a high LUMO energy level of −3.79 eV. Meanwhile, blend morphology of NBDTP-based OPVs shows fine tunability via thermal annealing. Owing to the beneficial optical absorption, suitable energy-level alignment, favorable molecule packing, and proper morphology, the optimized NBDTP-based OPVs achieve a power conversion efficiency of up to 10.1%, which exemplifies the potential of utilizing molecular acceptors featuring ladder-type heteroarenes for high-performance OPVs.