The excited states and electronic energy transfer of cyano-substituted organic materials: A many-body Green’s function theory study

Cyano substitution on organic material is an efficient strategy for developing the halogen-free organic solar cells (OSCs) with high performance. Recently, PCN2 based on electron-withdrawing dicyanobenzotriazole is constructed with high power conversion efficiency (PCE). However, the deep intrinsic elucidation of the exciton transition and electronic energy transfer (EET) about it is deficient. From many-body Green’s function theory, we compared the singlet and triplet states of the HTAZ, monoCNTAZ, diCNTAZ and PCN2 donors. We found the special CT composition of PCN2 and provide a scheme about the first CT. Selecting IDT-IC, IDT-IC-B and IDT-IC-T as the acceptors, we constructed different heterojunctions to study the EET. The couplings, especially overlap coupling, can be affected by conjugated side chains. When two neighbor blocks respectively from donor and acceptor have different electronegativity, the EET of the heterojunction will significantly enhance. It provides a methodology for designing the superior organic photovoltaic materials in the future.