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

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