Controlling the Cyano-Containing A2 Segments in A2-A1-D-A1-A2 Type Non-Fullerene Acceptors to Combine with a Benzotriazole-Based p-Type Polymer: Same-Acceptor-Strategy for High VOC Organic Solar Cells

To achieve efficient organic solar cells (OSCs), the design of promising non-fullerene small molecular acceptors (SMAs) is crucially important and the relationship between the chemical structure and optoelectronic properties needs to be further investigated. Herein, an A(2)-A(1)-D-A(1)-A(2) molecular skeleton is adopted to study the effect of end-capped A(2) groups containing different numbers of cyano units, where D and A(1) are fixed as indacenodithiophene (IDT) and benzotriazole (BTA) units, respectively. Utilizing the same-acceptor-strategy, three BTA-based SMAs, named as BTA701, BTA3, and BTA703, are paired with a BTA-based p-type polymer J71. The open-circuit voltage (V-OC) gradually decreases with the enhancement of electron-accepting ability of terminal A(2) units, from 1.32 V (BTA701) to 1.20 V (BTA3) and to 0.85 V (BTA703). The device J71:BTA3 eventually shows the best power conversion efficiency (PCE) of 8.60% with a V-OC up to 1.2 V because of the complementary light absorption, high and balanced hole and electron mobility, suitable phase separation, and crystallinity. This study indicates that appropriate cyano-containing units in BTA-based SMAs can effectively modulate the absorption, energy levels, charge mobility and surface free energy, which can provide valuable insights to the further design of SMAs. In addition, these results prove that the same-acceptor-strategy is simple and effective to realize a V-OC as high as 1.2V.