Terthiophene based non-fused electron acceptors for efficient organic solar cells

Designing electron acceptors with fully non-fused chemical structures is an effective method to solve the cost issue in the application of organic solar cells (OSCs). In this work, two A-D-A type non-fullerene acceptors (NFAs) with easy synthesis processes, namely A3T-2 and A3T-5, were designed and synthesized by using non-fused terthiophene as the D-skeleton and “open mode” or “closed-loop mode” substituted functional groups as the side chain modifiers, respectively. The two NFAs show similar molecular energy levels, while the calculation results and the absorption spectra indicate that A3T-5 has a more stable and planar conformation, which is beneficial to realize efficient charge transport capability. The OSCs based on A3T-2 and A3T-5 were fabricated by using PBDB-TF as the electron donor in parallel, and the power conversion efficiencies are 6.20% and 7.03%, respectively, which are high values among the OSCs based on non-fused NFAs with terthiophene as D-cores. The more stable planar molecular conformation of A3T-5 and the lower miscibility in the PBDB-TF: A3T-5 blend enabled the higher current and the PCE obtained in PBDB-TF: A3T-5-based OSC than that of PBDB-TF: A3T-2-based one. This work shows great potential in realizing efficient photovoltaic properties by employing non-fused acceptors via appropriate molecular design.