A Dithienyl Benzotriazole-based Polyfluorene: Synthesis and Applications in Polymer Solar Cells and Red Light-Emitting Diodes

A new donor-acceptor type polyfluorene derivative, poly[9,9-dioctyl-2,7-fluorene-alt-(4,7-bis(2'-thienyl)-2-octyl-2,1,3-benzotriazole)] (PFDTBTz), is synthesized by a Suzuki cross-coupling polymerization reaction. The optical, electrochemical, photovoltaic, and electroluminescence properties of PFDTBTz are investigated in detail. The maximum power conversion efficiency (PCE) of the PSCs based on PFDTBTz/PC71BM (1:2 w/w) reaches 2.1% with a short circuit current density (J(sc)) of 5.73 mA . cm(-2), an open circuit voltage (V-oc) of 0.84 V, and a fill factor (FF) of 0.44 under AM 1.5G, 100 mW . cm(-2) illumination. Polymer light-emitting diodes (PLEDs) are fabricated in an ITO/PEDOT:PSS (30 nm)/PFDTBTz (60 nm)/BAlq (40 nm)/Cs2CO3:Ag configuration and light emission is observed at a voltage greater than 8.0 V. The EL device shows almost pure red and the efficiency is very stable when the current density is increased, making it useful for commercial applications.