Constructing Efficient Fully Non‐Fused Ring Electron Acceptor with Locked‐In‐Cavity Crystal Structure by Simple Polarized Design

Abstract

Fully non‐fused ring electron acceptors (f‐NFREAs) are promising candidates for efficient organic photovoltaics (OPVs) due to their cost‐effectiveness, but efficiency and stability are limited by non‐ideal crystal stacking in the conjugation region and disordered alkyl chain arrangements in the cavity. Herein, a simple polarized design is proposed for constructing f‐NFREAs, where symmetric synthesis enables asymmetric conformations by utilizing the multiple orientations of terminal chlorine atoms on the alkyl chains. The resulting R3‐Cl molecule, based on a simple thiophene‐benzene‐thiophene tricyclic backbone, possesses a unique locked‐in‐cavity single crystal structure with a well‐defined 3D interchain crosslinked network. This crystal structure not only aids in fast exciton dissociation at the interface and charge transport within the domain but also facilitates a prolonged film‐formation process that promotes better crystal growth and more stable blend morphology. As a result, the OPV device based on the D18:R3‐Cl blend delivered a high efficiency of 16.87% with improved device stability. This efficiency further increased to 17.74% by incorporating another f‐NFREA, R4‐Cl, as the third component, representing the highest reported efficiency for simple tricyclic f‐NFREAs. This work presents a simple and innovative design strategy for polarized molecules, offering a cost‐effective approach to achieving higher efficiency and stability for OPVs.