Benzo[1,2-b:4,5-b']diselenophene-fused nonfullerene acceptors with alternative aromatic ring-based and monochlorinated end group: new synergistic strategy to simultaneously achieve highly efficient organic solar cells with energy loss of 0.49 eV

A new synergistic strategy using electron-rich core units and altering the aromatic structure-based 1,1-dicyanomethylene-3-indanone (IC) as end-groups for nonfullerene PSCs is reported and investigated how to obtain excellent PCE with extreme low Eloss simultaneously. Specifically, two Benzo[1,2-b:4,5-b']diselenophene-based, A-D-A-type chlorinated NF-SMAs (BDSeThCl and BDSePhCl) are synthesized, which are linked with a new 2-chlorothienyl-based IC and a conventional monochlorinated phenyl-based IC as end-group, respectively. BDSePhCl exhibited a wider and red-shifted absorption and downshifted energy levels than that of BDSeThCl. The blend films of BDSePhCl:PM7 perform better charge generation properties, more suitable phase separation, and more balanced charge mobilities in comparison with that of BDSeThCl:PM7. Therefore, compared to the best PCE of 11.91% with Eloss of 0.58 eV for BDSeThCl:PM7 blends, the optimal BDSePhCl:PM7 blends show an enhanced PCE of 13.68% with reducing Eloss of 0.49 eV. Notably, the excellent PCE of 13.68% is the highest record for A-D-A-type NF-SMAs with monochlorinated IC group in binary PSCs. The Eloss of 0.49 eV is the lowest value reported for A-D-A typed NF-SMAs in binary PSCs with PCE >13%. These results demonstrate that tailoring the monochlorinated aromatic ring-based IC is an effective strategy to improve the PCE and reduce the Eloss simultaneously in binary PSCs.