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4,5‐Ethylene‐2,7‐Carbazole‐Based Medium‐Bandgap Conjugated Polymers with Low‐Lying HOMO Levels Toward Efficient Polymer Solar Cells with High Open‐Circuit Voltage
Author(s) -
Sun Jiangman,
Zhu Yongxiang,
Xu Xiaofeng,
Zhang Chen,
Chen Junwu,
Chen Hongzheng,
Cao Yong
Publication year - 2014
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.201400001
Subject(s) - carbazole , polymer solar cell , materials science , polymer , band gap , conjugated system , copolymer , open circuit voltage , solar cell , energy conversion efficiency , polymer chemistry , active layer , optoelectronics , side chain , short circuit , photochemistry , chemical engineering , chemistry , layer (electronics) , nanotechnology , voltage , composite material , thin film transistor , physics , quantum mechanics , engineering
Three medium‐bandgap polymers based on a 4,5‐ethylene‐2,7‐dithienyl carbazole as the electron‐donating unit and different 5,6‐dialkoxy‐2,1,3‐benzothiadiazoles as the electron‐accepting units, are synthesized as polymer donors for photovoltaic applications. The three copolymers possess highest occupied molecular oribital (HOMO) levels around −5.47 eV and medium bandgaps of about 1.94 eV. The solar cells with polymer:[6,6]‐phenyl C71‐butyric acid methyl ester (PC 71 BM) = 1:4 as the active layer, show an especially high open‐circuit voltage ( V oc ) of 0.95 V and attain good power conversion efficiency up to 5.91%. The hole mobilities of the active layer films, measured by space‐charge‐limited current (SCLC), are up to 3.5 × 10 −4 cm 2 V −1 s −1 . Given the favorable medium bandgaps, low‐lying HOMO levels, and good hole mobilities, these copolymers are promising candidates for the construction of a highly efficient front cell to harvest the shorter wavelength band of the solar radiation in a tandem solar cell with high V oc .