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

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 $3.8{\times}10^{-3}cm^2V^{-1}s^{-1}$ . Bulk heterojunction photovoltaic cells are fabricated, with a conventional device structure of ITO/PEDOT:PSS/polymer: $PC_{71}BM$ /Ca/Al ( $PC_{71}BM$ = [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: $PC_{71}BM/MoO_3$ /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.