1,1-Dicyanomethylene-3-Indanone End-Cap Engineering for Fused-Ring Electron Acceptor-Based High-Performance Organic Photovoltaics

Organic photovoltaics (OPVs) have developed rapidly since the advent of fused-ring electron acceptors (FREAs). FREAs bearing bulky fused-ring cores, end-capped with electron-withdrawing groups, present advantages such as broad absorption, tunable frontier orbital levels, and good thermal stability. Recent breakthroughs demonstrate that FREA-based OPVs have achieved more than 17% efficiency, among which the end groups (EGs) of 1,1-dicyanomethylene-3-indanone (IC) and derivatives are critical for the performance enhancement. To date, more than 50 IC derivatives have been reported to construct high-performance FREA-based OPVs. In this review, we first introduce the chemical structure and synthesis route of the IC group. We discuss and classify the recent progress of FREAs based on IC and its derivatives, as well as the impact of IC on the morphology. We consider the issues the IC EGs face, including stability, isomerism, and EG redistribution, finally proposing some future directions for FREAs based on IC and its derivatives.