Synthesis and photovoltaic property of polymer semiconductor with phthalimide derivative as a promising electron withdrawing material

Donor–acceptor type (DA-type) polymeric photovoltaic material with a dicarboxylic imide-substituted benzene (phthalimide) derivative as electron-withdrawing units, poly[4,4′-didodecyl-2,2′-bithiophene-co-5,5′-(3,6-bis(thieno-2-yl)-N-octyl-phthalimide] (PDBTTPT), was synthesized by a Stille coupling reaction. It had an optical band gap of 1.96 V and a relatively low HOMO energy level of −5.34 eV in spite of it being a thiophene-based polymer. Photovoltaic devices with PDBTTPT/PC71BM active layers were fabricated under a variety of conditions for optimizing device performance. PDBTTPT exhibited the best power conversion efficiency (PCE) of 1.5% in the device where 80 wt.% of the PC71BM was contained in the active layer (PDBTTPT:PC71BM = 1:4, w/w) and which was pre-annealed at 120 °C for 10 min. In addition, a device which was pre-annealed at 140 °C for 10 min and a device which was post-annealed at 120 °C for 10 min showed analogous PCE values of 1.5% as well, although small differences were exhibited between various parameters, such as VOC, JSC, and FF.

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► A DA-type photovoltaic material (PDBTTPT) with a phthalimide derivative as electron-withdrawing units.
► It exhibited low HOMO energy level of −5.34 eV in spite of it being a thiophene-based polymer.
► Photovoltaic cells with various active layer forming conditions were fabricated.
► PDBTTPT exhibited the best power conversion efficiency (PCE) of 1.5%.