Synthesis of low band-gap 2D conjugated polymers and their application for organic field effect transistors and solar cells

Two donor-acceptor (D-A) 2-dimensional (2D) conjugated polymers P1 and P2 based on isoindigo (ID) and thienoisoindigo (TID) as acceptor unit and 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b´]dithiophene (BDT-T) as donor unit were prepared via Stille coupling and characterized by solution-possessed organic field effect transistors (OFETs) and organic solar cells (OSCs), respectively. By changing the electron-withdrawing component of the conjugated polymer backbone from ID to TID, there have also been diversities in the optical absorption, thermal stability, molecular structure, electrochemical energy level, charge mobility and photovoltaic properties of these two polymers. P1 and P2 exhibited intrinsic p-type semiconductor characteristic with hole mobilities of 3.0 × 10⁻² and 1.2 × 10⁻² cm² V⁻¹ s⁻¹, respectively. When blended with the [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM), the highest power conversion efficiency (PCE) of P1 and P2 were 2.40% and 1.28%, respectively. Our results suggest that ID and TID units are useful building blocks for the further development of efficient organic optical-electrical materials.