Novel D(A-Ar)2 type small molecules with oligothiophene, diketopyrrolopyrrole and benzo[4,5]thieno [2,3-b]indole units: investigation on relationship between structure and property for organic solar cells

Abstract

Two novel D(A-Ar)2 type small molecules (SMs) of 3T(DPP-BTI)2 and 4T(DPP-BTI)2 were synthesized and characterized, which contain diketopyrrolopyrrole (DPP) arms, 6-dodecyl-6H-benzo[4,5]thieno[2,3-b]indole (BTI) terminals, and oligomerthiophene donor unit (3T=trithiophene, 4T=tetrathiophene). The relation-ship between structure and property was investigated. Compared with their corresponding parent A-D-A type SMs, both D(A-Ar)2 type SMs exhibited a significantly increasing circuit current density (Jsc) by 1.39∼1.59 times and hole mobility (μh) by one order of magnitude, as well as a comparable power conversion efficiency (PCE) in their OPV and hole-only devices. The better photovoltaic properties with PCE of 3.02% and Jsc of 10.41 mA cm−2 were obtained in the 3T(DPP-BTI)2 based OPV cells. It indicates that appending the BTI terminal unit into A-D-A-type SMs is beneficial to increasing the Jsc and μh values of its resulting D(A-Ar)2 type SMs in their corresponding devices.