Fluorine substituted thienyl-quinoxaline copolymer to reduce the highest occupied molecular orbit level and increase open-circuit voltage for organic solar cells
An alternating polymer (FTTQ) based on fluorine substituted thienyl-quinoxaline as electron-withdrawing unit was synthesized and characterized. FTTQ showed similar absorption property in comparison with that of the counterpart polymer without fluorine atom (synthesized TTQ). However, the low-lying highest occupied molecular orbit (HOMO) energy level of FTTQ was –5.30 eV, about 0.24 eV smaller than that of synthesized TTQ (–5.06 eV). In order to study the photovoltaic properties of the materials, polymer solar cells (PSCs) were fabricated with FTTQ as donor blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor, as well as with an alcohol/water-soluble conjugated polymer, poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)](PFN) as a cathode interlayer. The PSCs incorporating the PFN interlayer showed significant and simultaneous enhancement in open-circuit voltage (V oc), short-circuit current density (J SC) and fill factor (FF), which leaded to a PCE of 2.59% for an optimized FTTQ:PC71BM weight ratio of 1:2 with THF vapor annealing for 30 s, in comparison with that of synthesized TTQ-based device (PCE of 1.41%). These findings will be of importance for achieving high-performance of polymer solar cells by functional group substitution in low band gap polymers.
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Document Type: Research Article
Publication date: February 1, 2016
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