Photovoltaic performance enhancement using fluorene-based copolymers containing pyrene units

Abstract

A set of novel conjugated polyfluorene co- polymers, poly[(9,9-didecylfluorene-2,7-diyl)-co-(4,7-di-2-thienyl- 2,1,3-benzothiadiazole-5,5-diyl)-co-(pyrene-1,6-diyl)], are synthesized via Pd(II)-mediated polymerization from 2,7-bis(4,4,5, 5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-di-n-decylfluorene, 4, 7-di(2-bromothien-5-yl)-2,1,3-benzothiadiazole, and 1,6-dibromopyrene with a variety of monomer molar ratios. The field-effect carrier mobilities and optical, electrochemical, and photovoltaic properties of the copolymers are systematically investigated. The hole mobilities of the copolymers are found to be in the range 7.0 x 105 8.0 x 104 cm2 V1 s1 and the on/off ratios were 8 x 103 7 x 104. Conventional polymer solar cells (PSCs) with the configuration ITO/PEDOT:PSS/polymer:PC71BM/LiF/Al are fabricated. Under optimized conditions, the polymers display power conversion efficiencies (PCEs) for the PSCs in the range 1.993.37% under AM 1.5 illumination (100 mW cm2). Among the four copolymers, P2, containing a 2.5 mol % pyrene component incorporated into poly[9,9-didecylfluorene-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PFDTBT) displays a PCE of 3.37% with a short circuit current of 9.15 mA cm2, an open circuit voltage of 0.86 V, and a fill factor of 0.43, under AM 1.5 illumination (100 mW cm2). (c) 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 1512,-1519