Alkoxy Substitution on Simple Non-Fused Electron Acceptors for Tuning the Photoelectric Properties of Organic Solar Cells

In order to identify high-performance non-fused ring electron acceptors for bulk heterojunction (BHJ) solar cells, six structurally diverse molecules are designed and categorized into two series. The first series is anchored by R1 as the reference molecule, featured fixed BDT, IC-2F end groups and modified pi bridges. The second series is anchored by R2 as the reference molecule, incorporated a terminal IC-2F and a central core modified with EDOT bridge. The electronic structure and photoelectric properties of all acceptor molecules were investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Charge transfer matrix (CTM), Density of states (DOS) and Reorganization energy (RE) etc. were analyzed to provide fundamental knowledge on charge transport and electronic excitation. Among the studied molecules, W2 exhibited a smaller energy gap (1.74 eV) compared to the other molecules, effectively transferring its electron from HOMO to LUMO. At the same time, the W2 molecule has excellent Voc and FF. Furthermore, W2 displayed the largest lambda max redshift compared to R1. Although W3 had a smaller value of lambda h, the comprehensive photovoltaic parameters of W2 were more excellent. The research results not only demonstrated the feasibility of introducing different alkoxy groups to alter the structure of the pi bridge and central core is a feasible method for constructing high-performance NFREAs, but also highlighted that BDT cores combined with EDOT bridges are among the most promising small molecule acceptors (SMAs) that could be considered as reasonable candidates for synthesis and incorporation into organic solar cells. The results of this study are expected to provide seminal ideas for the design of high-performance non-fullerene acceptors.