Synthesis and Characterization of a New Wide Bandgap Donor Polymer through Direct Arylation Polycondensation Method for Enhanced Performance in Ternary Non-Fullerene Organic Solar Cells.

The ternary active layer approach has emerged as a promising approach to further boost the power conversion efficiency of organic solar cells. In order to absorb photons from the solar radiation below 600 nm, we have designed and synthesized a new wide bandgap polymer P(FCzNDT-DFTPhz) consisting of strong 5,6-bis(6-fluoro-9H-carbazol-3-yl)naphtho[2,1-b:3,4-b']dithiophene and di-fluoro-dithieno [3,2-a:2',3'-c]phenazine donor and acceptor units, respectively, its optical and electrochemical properties were investigated. The P(FCzNDT-DFTPhz) exhibits strong absorption spectrumbelow 650 nm along with deeper HOMO energy level (-5.46 eV), which is beneficial for attaining high open circuit voltage. Utilizing P(FCzNDT-DFTPhz) as donor and Y6 as acceptor, the organic solar cells fabricated under ambient conditions, processed with non-halogenated solvent (toluene) attained a power conversion efficiency of 15.59% which is higher than that for PTB7-Th:Y6 counterparts (12.98%). When P(FCzNDT-DFTPhz) is incorporated into PTB7-Th:Y6 binary active layer, the ternary organic solar cells fabricated under ambient conditions, attained power conversion efficiency of 17.36%, which is due to the fact that P(FCzNDT-DFTPhz) and PTB7-Th exhibits complementary absorption spectra, increasing thelight harvesting efficiency and exciton generation rate. This leads to a simultaneous increase in short circuit current and fill factor, originated exciton utilization via energy transfer from P(FCzNDT-DFTPhz) to PTB7-Th, efficient exciton dissociation owing to increase D/A interfaces in ternary active layer, higher charge carrier mobilities and well-balanced charge transport, suppressed carrier recombination and fast charge extraction time and prolonged charge carrier lifetime.