Synthesis and characterization of a wide-bandgap polymer based on perfluorinated and alkylthiolated BDT with a deep HOMO level for organic photovoltaics
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A perfluorinated and alkylthiolated BDT-ttTPD-based donor polymer (P2FS-ttTPD) was synthesized via a Stille polymerization, and found to have a number average molecular weight (Mn) of 13,000 g/mol (Đ = 2.3). P2FS-ttTPD has a wide bandgap (1.96 eV) and a deep highest occupied molecular orbital (HOMO) level (−5.70 eV). The perfluorination and alkylthiolation of the polymer backbone lower the polymer’s HOMO level significantly. The hole and electron mobilities of P2FS-ttTPD were determined to be 1.12 x 10-4 and 9.38 x 10-7 cm2/Vs respectively. Polymer solar cell devices prepared with a P2FS-ttTPD:IT-4F (1:1) blend as the active layer were found to exhibit power conversion efficiencies of 4.15%, a short-circuit current density (JSC) of 10.29 mA/cm2, an open-circuit voltage (VOC) of 0.97 V, and a fill factor (FF) of 41.6%. The (1:1) blend devices were found to exhibit high VOC and low Eloss values.