Facile synthesis of 1-(2,6-diisopropylphenyl)-2,5-di(2-thienyl)pyrrole-based narrow band gap small molecules for solar cell applications

In this study, 1-(2,6-diisopropylphenyl)-2,5-di(2-thienyl)pyrrole-based two new low band gap organic small molecules, TPT-SM1 and TPT-SM2, were prepared and their optical, electrical and photovoltaic properties were investigated. TPT-SM1 was synthesized by simply linking the electron rich 1-(2,6-diisopropylphenyl)-2,5-di(2-thienyl)pyrrole and electron deficient tricyanovinyl (−C(CN)C(CN)2) units. On the other hand, TPT-SM2 was prepared by attaching the electron donating non planar triphenyl amine and electron accepting tricyanovinyl groups respectively on both side of 1-(2,6-diisopropylphenyl)-2,5-di(2-thienyl)pyrrole unit. Interestingly, the absorption band of TPT-SM1 and TPT-SM2 was found to be located exactly at the maximum solar flux region of the solar spectrum and their strong absorption band appears at the region of 470–800 nm and 490–900 nm, respectively, in film state. The optical band gap of TPT-SM1 and TPT-SM2 was calculated to be 1.58 eV and 1.42 eV, respectively, and the electrochemical studies revealed that the HOMO energy level was located at around −5.15 eV. The solution processed small molecule organic solar cells (SMOSCs) prepared by using TPT-SM1 and TPT-SM2 as an electron donor and PC71BM as an electron acceptor at 1:2 wt% donor:acceptor blend ratio showed maximum power conversion efficiency (PCE) of 1.19% and 1.68%, respectively.