Ternary Polymer Solar Cells with Low-Cost P3HT as the Second Donor by the Complementary Absorption Region from Long-Wavelength to Medium-Wavelength Regions Forming Cascaded HOMO and LUMO Energy Levels

In this work, ternary polymer solar cells (PSCs) were constructed with PTB7-Th as the host donor, O-IDTBR as the acceptor, and P3HT as the third component material. Two binary PSCs showed different advantages. The PTB7-Th-based binary PSCs showed the advantage of high V-OC (1.03 V), while P3HT-based binary PSCs showed the advantage of a high fill factor (FF) (69.52%). P3HT can complement the medium-wavelength absorption spectra and allows efficient exciton dissociation due to the cascade's lowest unoccupied molecular orbital and highest occupied molecular orbital level between P3HT, PTB7-Th, and O-IDTBR. Therefore, the optimized ternary PSCs combine the advantage of two binary PSCs. The optimized ternary PSCs showed higher J(SC) and FF than PTB7-Th-based binary PSCs and higher V-OC than P3HT-based binary PSCs. P3HT can simultaneously enhance the arrangement of the blend donor to enhance crystallization, decrease roughness, and improve charge-carrier kinetic processes. In addition, the optimized ternary PSCs showed better thermal stability than PTB7-Th-based binary PSCs.