New wide-bandgap D–A polymer based on pyrrolo[3,4-b] dithieno[2,3-f:3′,2′-h]quinoxalindione and thiazole functionalized benzo[1,2-b:4,5-b′]dithiophene units for high-performance ternary organic solar cells with over 16% efficiency

We have designed a simple and new D–A copolymer (PDTQxD-BDTTZ) denoted as P125 based on 8H-pyrrolo[3,4-b]dithieno[3,2-f:2′,3′-h]quinoxaline-8,10(9H)-dione (PDTQxD) and thiazole functionalized benzo[1,2-b:4,5-b′]dithiophene (BDTTZ) as acceptor and donor units, respectively, and its optical and electrochemical properties are investigated in detail. P125 showed a deeper HOMO energy level and broad absorption from 300 nm to 680 nm. P125 is used as a donor for the fabrication of binary and ternary polymer solar cells using two non-fullerene small molecule acceptors i.e., medium bandgap DBTBT-IC and narrow bandgap Y6. The optimized P125:DBTBT-IC:Y6 (1 : 0.2 : 1.0) ternary-based polymer solar cell attained overall PCE of 16.44%, which is higher than that for optimized binary P125:DBTBT-IC (12.23%) and P125:Y6 (13.09%). The incorporation of DBTBT-IC as the third component not only imparts the energy transfer from DBTBT-IC to Y6 but also optimizes the morphology and nanoscale phase separation in the active layer, leading to balanced charge transport and reduced charge recombination. The enhanced photovoltaic performance of ternary-based polymer solar cells is a result of the strong crystallization of DBTBT-IC.