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

• Published in: Macromolecular chemistry and physics Vol. 215; no. 11; pp. 1052 - 1059
• Main Authors: Sun, Jiangman, Zhu, Yongxiang, Xu, Xiaofeng, Zhang, Chen, Chen, Junwu, Chen, Hongzheng, Cao, Yong
• Format: Journal Article
• Language: English
• Published: Weinheim Blackwell Publishing Ltd 01.06.2014; Wiley; Wiley Subscription Services, Inc
• Subjects: 3-benzothiadiazole; 4,5‐ethylene‐2,7‐carbazole; 5,6‐dialkoxy‐2,1,3‐benzothiadiazole; 5-ethylene-2; 6-dialkoxy-2; 7-carbazole; Applied sciences; conjugated polymers; Copolymers; Electric potential; Energy; Energy conversion efficiency; Energy gaps (solid state); Exact sciences and technology; medium bandgaps; Molecular orbitals; Natural energy; Organic polymers; Photovoltaic cells; Photovoltaic conversion; Physicochemistry of polymers; polymer solar cells; Polymers with particular properties; Preparation, kinetics, thermodynamics, mechanism and catalysts; Solar cells; Solar cells. Photoelectrochemical cells; Solar energy; Volatile organic compounds; Voltage; Substituent effect; Terpolymer; 4,5-ethylene-2,7-carbazole; Short circuit currents; Solution polycondensation; Carbazole derivative copolymer; Hole mobility; Thiophene copolymer; polymer solar cells; Organic solar cells; Experimental study; Fill factor; Open circuit voltage; Suzuki coupling; 5,6-dialkoxy-2,1,3-benzothiadiazole; Electrochemical properties; Conjugated copolymer; Optical properties; Preparation; Aromatic copolymer; medium bandgaps; Optical absorption; conjugated polymers
• ISSN: 1022-1352; 1521-3935
• DOI: 10.1002/macp.201400001

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 (PC71BM) = 1:4 as the active layer, show an especially high open‐circuit voltage (Voc) 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 cm2 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 Voc. D–A conjugated polymers of 4,5‐ethylene‐2,7‐dithienyl carbazole and 5,6‐dialkoxy‐2,1,3‐benzothiadiazoles possess deep highest occupied molecular orbital (HOMO) levels around −5.45 eV and medium bandgaps of about 1.94 eV. Their polymer solar cells show a high Voc of 0.95 V and good power conversion efficiency (PCE) up to 5.91%, which is promising as a front cell for harvesting the shorter‐wavelength band of solar radiation in a tandem solar cell.