A bromine and chlorine concurrently functionalized end group for benzo[1,2-b:4,5-b']diselenophene-based nonfluorinated acceptors: new hybrid strategy to balance the crystallinity and miscibility of blend films enabling highly efficient polymer solar cells

摘要： A bromine and chlorine concurrently functionalized end group for nonfluorinated benzo[1,2-b:4,5-b']diselenophene-based acceptors: new hybrid strategy to balance the crystallinity and miscibility of blend films enabling highly efficient polymer solar cells. Dihalogenated 1,1-dicyanomethylene-3-indanone (IC) plays a key role in top-performing fused-ring electron acceptors (FREAs)-based polymer solar cells (PSCs). Here, we firstly synthesized a hybrid dihalogenated IC (IC-BrCl), which simultaneously grafted one Br atom and one Cl atom onto the same IC skeleton. Three nonfluorinated FREAs (BDSe-4Cl, BDSe-2(BrCl) and BDSe-4Br) are synthesized by employing benzo[1,2-b:4,5-b′]diselenophene-based core unit and dichlorinated IC, hybrid dihalogenated IC (IC-BrCl), and dibrominated IC for highly efficient PSCs, respectively. These three acceptors exhibit very similar absorption spectra with 1.39 eV of optical band gap, but slightly different in the HOMO/LUMO energy levels in thin films. The crystallinity of acceptors was progressively enhanced and miscibility with PM7 was gradually reduced with the increase of Br atoms. The BDSe-2(BrCl):PM7 blend films exhibited the strongest face-on crystallization orientation, the most proper phase separation feature, the highest and most balanced carrier mobility and the weakest charge recombination owing to the excellent balance of miscibility and crystallinity of blend film. Notably, BDSe-2(BrCl):PM7-based PSCs demonstrated an outstanding PCE of 14.5% with an impressive FF of 76.5%, which substantially outperformed its counterparts (13.8% for BDSe-4Cl, 13.2% for BDSe-4Br, respectively) and is the highest value in hybrid IC-based FREAs for binary PSCs. Our results demonstrated that hybrid dihalogenated IC with one Br atom and one Cl atom provide a promising strategy to tune crystallinity and miscibility of FREAs for boosting the FF and PCE of PSCs.