Efficient Polymer Solar Cells Employing Solution-Processed Conjugated Polyelectrolytes with Differently Charged Side Chains

Poly(6-(4,7-dimethyl-2H-benzo[d][1,2,3]triazol-2-yl)-N,N,N-trimethylhexan-1 aminium iodide) (PBTz-TMAI) and poly(sodium 4-(4,7-dimethyl-2H-benzo[d] [1,2,3]triazol-2-yl)butane-1-sulfonate) (PBTz-SO3Na) based on the same benzotriazole-conjugated backbone but with ammonium and sulfonated side chains are designed and synthesized through side-chain functionalization and Yamamoto polymerization, respectively, and are used as the cathode interlayers in fullerene- and non-fullerene-based polymer solar cells. The interfacial modification of PBTz-TMAI and PBTz-SO3Na onto the active layer achieves good energy alignment at cathode electrodes and optimized exciton-dissociation efficiency from the active layer. Consequently, the power conversion efficiencies (PCEs) of 7.8% and 9.6% are obtained for the fullerene PTB7:PC71BM-based and non-fullerene PBDB-T:ITIC-based polymer solar cells (PSCs) with PBTz-SO3Na interlayer. The PCS devices based on PTB7:PC71BM and PBDB-T:ITIC active layers with PBTz-TMAI interlayer achieved a remarkably improved performance with PCEs of 8.2% and 10.2%, respectively.