Manipulating the D:A interfacial energetics and intermolecular packing for 19.2% efficiency organic photovoltaics

Abstract

Manipulating the donor:acceptor (D:A) energetics, e.g., the highest occupied molecular orbital (HOMO) offset, is the key to balancing the charge separation and charge recombination for high-performance organic solar cells (OSCs). Herein, we designed and synthesized a non-fullerene electron acceptor, i.e., BTP-H2, which shows strong intermolecular interaction and near-zero HOMO offset when pairing with polymer donor PM6. Transient absorption spectroscopies unveil that BTP-H2 exhibits a long-lived intra-moiety charge-separation state, which contributes to efficient hole transfer or charge generation, irrespective of the small HOMO offset. In addition, the small energetic offset reduces the non-radiative loss for a high open-circuit voltage (V_oc). As a result, we demonstrate high-performance OSCs with the best power conversion efficiency (PCE) of 18.5%, a high V_oc of 0.932 V and a peak photon-to-electron response of ∼ 90%. Furthermore, ternary OSCs comprising PM6:BTP-H2:L8-BO exhibit a champion PCE of 19.2% (certified value of 18.8%) due to the improved balance between charge generation and charge recombination, and this represents the best among PCEs of single-junction OSCs.