Incorporation of Different Conjugated Linkers into Low Band Gap Polymers Based on 5,6-Bis(octyloxy)-2,1,3 benzooxadiazole for Tuning Optoelectronic Properties

Four new 2,1,3-benzooxadiazole-based donoracceptor conjugated polymers, namely poly{9-(9-heptadecanyl)-9H-carbazole-alt-5,6-bis(octyloxy)-4,7-di(selenophen-2-yl)benzo[ c][1,2,5] oxadiazole)}(PSBSC), poly{9-(9-heptadecanyl)-9H-carbazole- alt-5,6-bis(octyloxy)-4,7-di(furan-2-yl) benzo[c][1,2,5]oxadiazole)}(PFBFC), poly{9,9-dioctyl-9H-fluorene-alt-5,6bis( octyloxy)-4,7-di(selenophen-2-yl) benzo[c][1,2,5] oxadiazole)} (PSBSFL), and poly{9,9-dioctyl-9H-fluorene-alt-5,6-bis(octyloxy)- 4,7-di(furan-2-yl) benzo[c][1,2,5] oxadiazole)}(PFBFFL), were synthesized via Stille polycondensation reaction. All polymers were found to be soluble in common organic solvents such as chloroform, tetrahydrofuran, and chlorobenzene. Their structures were verified by 1 H-NMR and the molecular weights were determined by gel permeation chromatography (GPC). The polymer films exhibited broad absorption bands. Among all polymers, photovoltaic cells based on the device structure of ITO/PEDOT: PSS/PSBSC: PC71BM(1: 3, w/w)/LiF/Al revealed an open-circuit voltage of 0.62 V, a short circuit current of 7.63 mA cm 22 and a power conversion efficiency of 1.89%. This work demonstrates a good example for tuning absorption range, energy level, and photovoltaic properties of the polymers with different spacers and donor units can offer a simple and effective method to improve the efficiency of PSCs. (C) 2016 Wiley Periodicals, Inc