Conventional and Inverted Photovoltaic Cells Fabricated Using New Conjugated Polymer Comprising Fluorinated Benzotriazole and Benzodithiophene Derivative

Abstract

A new conjugated copolymer, poly{4,8-bis(triisopropylsilylethynyl)benzo[1,2-b:4,5-b']dithiophene-alt-4,7-bis(5-thiophen-2-yl)-5,6-difluoro-2-(heptadecan-9-yl)-2H-benzo[d][1,2,3]triazole} (PTIPSBDT-DFDTBTz), is synthesized by Stille coupling polycondensation. The synthesized polymer has a band gap energy of 1.9 eV, and it absorbs light in the range 300-610 nm. The hole mobility of a solution-processed organic thin-film transistor fabricated using PTIPSBDT-DFDTBTz is 3.8 x 10(-3) cm(2) V-1 s(-1). Bulk heterojunction photovoltaic cells are fabricated, with a conventional device structure of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al (PC71BM = [6,6]-phenyl-C-71-butyric acid methyl ester); the device shows a power conversion efficiency (PCE) of 2.86% with an open-circuit voltage (V-oc) of 0.85 V, a short-circuit current density (J(sc)) of 7.60 mA cm(-2), and a fill factor (FF) of 0.44. Inverted photovoltaic cells with the structure ITO/ethoxylated polyethlyenimine/polymer:PC71BM/MoO3/Ag are also fabricated; the device exhibits a maximum PCE of 2.92%, with a V-oc of 0.89 V, a J(sc) of 6.81 mA cm(-2), and an FF of 0.48.