Two Better Compatible and Complementary Light Absorption Polymer Donors Contributing Synergistically to High Efficiency and Better Thermally Stable Ternary Organic Solar Cells

High-performance and better thermal stability organic solar cells (OSCs) with two blended polymers (PBZ1 and PTB7-Th) as donors and L8-BO as an acceptor. The optimized films (the ratio of PBZ1:PTB7-Th:L8-BO is 0.8:0.2:1.3) ensure the effective suppression of hole recombination and efficient exciton dissociation due to the similar highest occupied molecular orbital (HOMO) energy levels of both PTB7-Th and PBZ1 and the cascade lowest unoccupied molecular orbital (LUMO) energy level among PBZ1, PTB7-Th, and L8-BO. The optimized ternary PSCs showed a power conversion efficiency (PCE) of 15.85%. The enhancement of PCE is attributed to PTB7-Th, which has a complementary light absorption of PBZ1:L8-BO binary films and enhanced long wavelength light absorption for the ternary films. The excellent thermal stability is mainly attributed to the high crystallization of the ternary photoactive layer. In addition, the optimized ternary films exhibit high crystallization and smooth surfaces even after 20 h of 80 °C thermal annealing. The study indicates that improved thermal stability and performance can be achieved by a ternary strategy with PBZ1:PTB7-Th:L8-BO (0.8:0.2:1.3) ternary films as the photoactive layer.