New acceptor–donor–acceptor-type conjugated molecules bearing naphtho[1,2-b:5,6-b′]dithiophene and (E)-1,2-di(thiophen-2-yl)ethene and their applications in thin-film transistors and photovoltaic cells

Abstract

We synthesized new diketopyrrolopyrrole (DPP)-based small molecules i.e., TVT(DPP)2 and NDT(DPP)2, containing (E)-1,2-di(thiophen-2-yl)ethene and naphtho[1,2-b:5,6-b′]dithiophene, respectively, as electron-donating moieties with almost identical conjugation lengths. To study the effect of the conjugation bridge between the DPP units on the performance of thin-film transistors (TFTs) and photovoltaic (PV) devices, we performed theoretical calculations and investigated the photophysical and electrochemical properties. Finally, TFTs and PV devices were fabricated, and their charge carrier mobilities and power conversion efficiencies (PCEs) with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) were measured. The hole mobility of TVT(DPP)2 was found to be larger than that of NDT(DPP)2. The solution-processed bulk-heterojunction PV devices based on TVT(DPP)2 and NDT(DPP)2 gave maximum PCEs of 2.21% and 3.03%, respectively.