2,1,3-Benzothiadiazole-5,6-dicarboxylic imide based low-bandgap polymers for solution processed photodiode application

Abstract

Six low-bandgap donor–acceptor polymers, PDIC20/8-BTh, PDIC20/8-BDT, and PDIC20/8-DTS, with 2,1,3-benzothiadiazole-5,6-dicarboxylic imide (DI) as the electron-accepting unit and BTh, BDT, and DTS as donors, were synthesized and investigated as photodetecting materials. All the polymers exhibited broad absorptions covering 300–900nm, low-lying LUMO energy levels, and good thermal stability. They were employed as active layers of photodetectors with the device configuration of ITO/PEDOT:PSS/active layer (polymer:PC61BM)/C60/Al by solution casting method. With C60 as an electron-extracting as well as hole-blocking layer, the dark currents were effectively reduced and the obtained photodetectors exhibited high detectivities (∼1012 Jones) with panchromatic coverage from the ultraviolet to near-infrared region at low operating voltage and room temperature. The device made of PDIC20-BTh bahaved better comprehensive performance including high photocurrent, low dark current, and superior spectral range than others. Gaussian calculations were conducted to better understand the distinguishing performances of polymer photodetectors at the molecular level. The conformations of both donor and acceptor units played important roles in determining the overall performance.