Synthesis and Characterization of a Soluble A–D–A Molecule Containing a 2D Conjugated Selenophene‐Based Side Group for Organic Solar Cells

A new acceptor–donor–acceptor (A–D–A) small molecule based on benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) is synthesized via a Stille cross‐coupling reaction. A highly conjugated selenophene‐based side group is incorporated into each BDT unit to generate a 2D soluble small molecule (SeBDT‐DPP). SeBDT‐DPP thin films produce two distinct absorption peaks. The shorter wavelength absorption (400 nm) is attributed to the BDT units containing conjugated selenophene‐based side groups, and the longer wavelength band is due to the intramolecular charge transfer between the BDT donor and the DPP acceptor. SeBDT‐DPP thin films can harvest a broad solar spectrum covering the range 350–750 nm and have a low bandgap energy of 1.63 eV. Solution‐processed field‐effect transistors fabricated with this small molecule exhibit p‐type organic thin film transistor characteristics, and the field‐effect mobility of a SeBDT‐DPP device is measured to be 2.3 × 10^?3 cm² V^?1 s^?1. A small molecule solar cell device is prepared by using SeBDT‐DPP as the active layer is found to exhibit a power conversion efficiency of 5.04% under AM 1.5 G (100 mW cm^?2) conditions.