Synthesis and characterization of π-conjugated polymer based on phthalimide derivative and its application for polymer solar cells

Abstract

A new copolymer named T-TI24T (poly((5,5-(2-butyl-5,6-bisdecyloxy-4,7-di- thiophen-2-yl-isoindole-l,3-dione))-alt-(2,5-thiophene))) based on phthalimide derivative and thiophene is synthesized by the Stille-coupling reaction. The polymer shows relatively high number average molecular weight of 86500 g/mol with good solubility in common organic solvents such as chloroform, 1,2-dichlorobenzene, and toluene and is thermally stable up to 380 °C. Besides, it possesses a relatively low highest occupied molecular orbital (HOMO) energy level of -5.33 eV, promising the high open circuit voltage (V ∞) for photovoltaic applications. Active layer solution of polymer T-TI24T-as a donor and (6)-l-(3-(methoxycarbonyl)-{5}-l-phenyl[5,6]- fullerene (PCBM)-as an acceptor in different weight ratios is applied to fabricate the polymer solar cell devices. The ratio of polymer/PCBM affects the solar cell efficiency and the best performance exhibits in the device with polymer/PCBM = 1:3 (w/w), which shows a power conversion efficiency (PCE) of 0.199% and a V∞ of 0.99 V, respectively. Even though the device shows the very low PCE, the V∞ is higher than that of well known bulk heterojunction type solar cell based on P3HT:PC61BM (c.a. 0.5 V).