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

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 300-900 nm, 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)/C-60/Al by solution casting method. With C-60 as an electron-extracting as well as hole-blocking layer, the dark currents were effectively reduced and the obtained photodetectors exhibited high detectivities (similar to 10(12) 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. (C) 2015 Elsevier B.V. All rights reserved.National Natural Science Foundation of China - China [51403203, 21322404, 20834001]; Research Fund for Doctoral Program of Higher Education of MOE of China [20130001130002]SCI(E)EIARTICLEjz10@pku.edu.cn; mdg1014@ciac.jl.cn; xhwan@pku.edu.cn305-3132