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Layer‐by‐Layer Deposition of Rhenium‐Containing Hyperbranched Polymers and Fabrication of Photovoltaic Cells
Author(s) -
Tse Chui Wan,
Man Ka Yan Kitty,
Cheng Kai Wing,
Mak Chris S. K.,
Chan Wai Kin,
Yip Cho Tung,
Liu Zheng Tong,
Djurišić Aleksandra B.
Publication year - 2006
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.200600838
Subject(s) - materials science , photocurrent , polymer , open circuit voltage , thin film , ellipsometry , energy conversion efficiency , layer (electronics) , short circuit , analytical chemistry (journal) , chemical engineering , optoelectronics , nanotechnology , chemistry , organic chemistry , composite material , physics , quantum mechanics , voltage , engineering
Multilayer thin films were prepared by the layer‐by‐layer (LBL) deposition method using a rhenium‐containing hyperbranched polymer and poly[2‐(3‐thienyl)ethoxy‐4‐butylsulfonate] (PTEBS). The radii of gyration of the hyperbranched polymer in solutions with different salt concentrations were measured by laser light scattering. A significant decrease in molecular size was observed when sodium trifluoromethanesulfonate was used as the electrolyte. The conditions of preparing the multilayer thin films by LBL deposition were studied. The growth of the multilayer films was monitored by absorption spectroscopy and spectroscopic ellipsometry, and the surface morphologies of the resulting films were studied by atomic force microscopy. When the pH of a PTEBS solution was kept at 6 and in the presence of salt, polymer films with maximum thickness were obtained. The multilayer films were also fabricated into photovoltaic cells and their photocurrent responses were measured upon irradiation with simulated air mass (AM) 1.5 solar light. The open‐circuit voltage, short‐circuit current, fill factor, and power conversion efficiency of the devices were 1.2 V, 27.1 μ A cm −2 , 0.19, and 6.1×10 −3 %, respectively. The high open‐circuit voltage was attributed to the difference in the HOMO level of the PTEBS donor and the LUMO level of the hyperbranched polymer acceptor. A plot of incident photon‐to‐electron conversion efficiency versus wavelength also suggests that the PTEBS/hyperbranched polymer junction is involved in the photosensitization process, in which a maximum was observed at approximately 420 nm. The relatively high capacitance, determined from the measured photocurrent rise and decay profiles, can be attributed to the presence of large counter anions in the polymer film.