Development of DA-type polymers with phthalimide derivatives as electron withdrawing units and a promising strategy for the enhancement of photovoltaic properties

We report on two push–pull type polymer semiconductors involving phthalimide derivatives as electron withdrawing units. The solubility and energy level of phthalimide could be easily controlled by introducing various functional groups in its nitrogen site. Additionally, the VOC value of polymer semiconductor materials with phthalimide as an electron withdrawing unit could be efficiently enhanced because of the low HOMO energy level of phthalimide. Nevertheless, there are just a few of studies regarding the use of phthalimide in OPVs. In this study, we synthesized two photovoltaic polymer materials based on phthalimide with high VOC value, PFTPT and PCTPT. Between the two polymers, PCTPT/PC71BM-based photovoltaic cell afforded the best PCE value of 1.4% (VOC=0.94 V, JSC=4.41 mA/cm2, FF=0.33) under 100 mW/cm2 irradiation. In addition, a promising strategy for the development of high performance photovoltaic polymers with phthalimide derivatives as electron withdrawing units was investigated.