Reducing Energy Loss and Morphology Optimization Manipulated by Molecular Geometry Engineering for Hetero‐junction Organic Solar Cells

Abstract

Summary of main observation and conclusionMolecular geometry engineering is an effective strategy to control the micromorphology and molecular energy level in organic photovoltaics (OPVs). Two novel copolymers based on alkylsilyl‐ and chloride‐functionalized benzodithiophene (BDT) were designed and synthesized for wide bandgap copolymer donor materials in OPVs. It was found that the two copolymers exhibited distinctly different properties in active layer when blended with fullerene‐free acceptor IT‐4F. The chloride‐functionalized copolymer PBDTCl‐TZ with deeper molecular energy level and better coplanar structure induced more ordered aggregation in blend film. Thus, the device based on PBDTCl‐TZ exhibits better energy alignment with IT‐4F and smaller radiative recombination. Furthermore, the non‐radiative recombination of PBDTCl‐TZ:IT‐4F based device is about 45 mV lower than the PBDTSi‐TZ:IT‐4F based device, contributing to a lower energy loss (Eloss), and a higher open‐circut voltage (VOC). As a result, the devices based on the blend of PBDTCl‐TZ:IT‐4F exhibit a high power conversion efficiency (PCE) of up to 12.2% with a high VOC of 0.837 V, higher than that of PBDTSi‐TZ:IT‐4F, of which the PCE is 11.2% with a VOC of 0.781 V.