Cationic Polyelectrolytes with Alkylsulfonate Counterions as a Cathode Interface Layer for High-Performance Polymer Solar Cells

Three cationic polyelectrolytes polyethyleneimine ethoxylate (PEIE)-1,4-butanediol dimethylsulfonate (MSB), PEIE-1,4-butanediol diethylsulfonate (ESB), and PEIE-1,4-butanediol dibenzylsulfonate (BSB), containing methylsulfonate, ethylsulfonate, and benzylsulfonate, respectively, were prepared for cathode interface layers (CILs) via a one-step reaction with 1,4-butanediol dialkylsulfonate and PEIE as the reactants. The results indicate that PEIE-MSB and PEIE-ESB with smaller counterions possess more efficient electron extraction, higher electron mobilities, and better photovoltaic performance than PEIE-BSB with larger counterions. The PTB7-Th:PC71BM-based single junction bulk heterojunction polymer solar cells (PSCs) with PEIE-ESB as the CIL showed power conversion efficiencies (PCEs) of 10.44 and 9.23% under the thickness conditions of 8 and 30 nm, respectively. The PM6:Y6-based PSCs displayed a high PCE of 15.69%. The study provides not only new high-performance CILs but also a new strategy to construct light-soaking-free PSCs via tuning alkylsulfonate counterions.