Dialkoxynaphthalene as an electron-rich unit for high-performance polymer solar cells with large open circuit voltages

Dialkoxynaphthalene is a simple aromatic building block, which can be synthesized easily in a large scale. In this work, two dialkoxynaphthalene derivatives were copolymerized with electron-withdrawing benzothiadiazole (BT) derivatives to afford three donor-acceptor copolymers, PNDTBT, PIVT2FTBT and PN2FTBT. The three copolymers have diverse bandgaps ranged from 1.73 to 1.86 eV, and deep HOMO energy levels up to -5.61 eV. Thermogravimetric analysis and electrochemical measurements show that these copolymers have good thermal and environment stability. The hole mobilities of these copolymers were investigated using the space charge limited current (SCLC) method as well as the organic field effect transistor (OFET) method. Polymer solar cells based on PNDTBT exhibit the best photovoltaic performance with a power conversion efficiency of 6.24% and a V-oc of 0.94 V, much better than those of previously reported copolymers based on dialkoxynaphthalene. (C) 2015 Elsevier Ltd. All rights reserved.