Benzooxadiazole-based donor/acceptor copolymers imparting bulk-heterojunction solar cells with high open-circuit voltages

Abstract

In this study we used Suzuki cross-coupling to synthesize three new donor/acceptor copolymers-PFTBO, PAF1130, and PCTBO-featuring soluble alkoxy-modified 2,1,3-benzooxadiazole (BO) moieties as acceptor units and electron-rich building blocks-dialkyl fluorene (F), alkylidene fluorene (AF), and carbazole (C), respectively-as donor units. These polymers, which we characterized using gel permeation chromatography, thermogravimetric analysis, NMR spectroscopy, UV-Vis absorption spectroscopy, and electrochemical cyclic voltammetry, exhibited good solubility, low-lying energy levels for their highest occupied molecular orbitals, excellent thermal stability, and air stability. Using these polymers, we fabricated bulk-heterojunction solar cell devices having the structure indium tin oxide/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate/polymer:[6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM) (1:1, w/w)/Ca/Al. Under AM 1.5G illumination (100 mW cm(-2)), the solar cell incorporating PFTBO exhibited a high value of V-OC of 1.04 V and that based on PCTBO provided a power conversion efficiency of 4.1% without the need for any post treatment. (C) 2012 Elsevier Ltd. All rights reserved.