Transannularly conjugated tetrameric perylene diimide acceptors containing [2.2]paracyclophane for non-fullerene organic solar cells

Abstract

Core engineering of perylene diimide (PDI)-based small molecular acceptors has played a critical role in boosting the device performances in the field of organic solar cells (OSCs). In this work, two regio-isomeric PDI-based acceptors (named oCP-FPDI4 and pCP-FPDI4) based on a novel [2.2]paracyclophane core were designed and synthesized. Due to the subtle variations in the functionalization positions on the [2.2]paracyclophane moiety, the two PDI acceptors exhibit different molecular geometries and absorption properties. When blended with a donor polymer named P3TEA, oCP-FPDI4 and pCP-FPDI4 showed dramatic differences in photovoltaic performances (2.42% vs. 9.06%). In-depth studies on the nano-scale morphology of the respective blend films revealed that the P3TEA:pCP-FPDI4 blend exhibited suitable phase segregation, thus contributing to better charge dissociation and less charge recombination. The marked variations in photovoltaic performances between oCP-FPDI4 and pCP-FPDI4 highlight the importance of regulating the spatial orientations in the design of PDI-based acceptors using cyclophane derivatives.