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Efficient Conventional‐ and Inverted‐Type Photovoltaic Cells Using a Planar Alternating Polythiophene Copolymer
Author(s) -
Lee Wonho,
Choi Hyosung,
Hwang Sungu,
Kim Jin Young,
Woo Han Young
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102883
Subject(s) - polythiophene , copolymer , planar , materials science , photovoltaic system , type (biology) , composite material , polymer , computer science , conductive polymer , electrical engineering , engineering , ecology , computer graphics (images) , biology
A low‐band‐gap alternating copolymer, poly{5,6‐bis(octyloxy)‐4‐(thiophen‐2‐yl)benzo[ c ]‐1,2,5‐thiadiazole} (PTBT), was synthesized and investigated for photovoltaic applications. PTBT showed a minimized torsion angle in its main backbone owing to the introduction of solubilizing octyloxy groups on the electron‐poor benzothiadiazole unit, thereby resulting in pronounced intermolecular ordering and a deep level of the HOMO (−5.41 eV). By blending PTBT with [6,6]phenyl‐C61‐butyric acid methyl ester (PC 61 BM), highly promising performance was achieved with power‐conversion efficiencies (PCEs) of 5.9 and 5.3 % for the conventional and inverted devices, respectively, under air mass 1.5 global (AM 1.5G, 100 mW cm −2 ) illumination. The open‐circuit voltage ( V OC ≈0.85–0.87 V) is one of the highest values reported thus far for thiophene‐based polymers (e.g., poly(3‐hexylthiophene) V OC ≈0.6 V). The inverted device also achieved a remarkable PCE compared to other devices based on low‐band‐gap polymers. Ideal film morphology with bicontinuous percolation pathways was expected from the atomic force microscopy (AFM) images, space‐charge‐limited current (SCLC) mobility, and selected‐area electron‐diffraction (SAED) measurements. This molecular design strategy is useful for achieving simple, processable, and planar donor–acceptor (D–A)‐type low‐band‐gap polymers with a deep HOMO for applications in photovoltaic cells.