Imide-free electron-deficient electrolytes with adjustable cathode-modifying capabilities achieved by side chain engineering for efficient organic solar cells

Cathode interlayers (CILs) play crucial roles in boosting the performance of organic solar cells (OSCs). Herein, a class of novel electron-deficient electrolytes, namely BDOPV-1 and BDOPV-2, based on the benzodifurandione-based oligo(p-phenylene vinylene) (BDOPV) building block and different quaternary ammonium-type side chains, are presented as cathode interface materials (CIMs) for OSCs. The altering of alkyl chains on quaternary ammonium groups is found to effectively regulate the work function-amending abilities, self-doping interactions, film-forming properties, and compatibility with active layers of CIMs. Consequently, BDOPV-2 incorporating ethyl chains possesses superior electron-extracting/transporting, carrier recombination–restraining and device stability-improving capabilities in OSCs compared to BDOPV-1 with methyl groups. As a result, the D18:Y6-based non-fullerene OSCs modified by BDOPV-1 and BDOPV-2 output power conversion efficiencies (PCEs) of 15.74% and 17.49%, respectively. On the other hand, in the D18:L8-BO system, BDOPV-1- and BDOPV-2-decorated devices realize PCEs of 17.06% and up to 18.54%, respectively. In brief, this work provides a class of promising CILs with universality for fabricating high-performance OSCs, and a possible reference for developing efficient CIMs via side chain intervention.