Layer-by-layer assembled transparent conductive graphene films for solar cells application
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Layer-by-layer assembled transparent conductive graphene films for solar cells application Ryousuke Ishikawa1, Masashi Bando1, Yasuyoshi Kurokawa2, Adarsh Sandhu1,3, Makoto Konagai2,4 1 Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8552, Japan 2 Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8552, Japan 3 Electronics-Inspired Interdisciplinary Research Institute (EIIRIS), Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan 4 Photovoltaics Research Center (PVREC), Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8552, Japan ABSTRACT The potential of chemically derived graphene as a solution-processable transparent conductive film has been explored. Synthesis of amine-functionalized graphene oxide was intended for its utilization in layer-by-layer assembly. Layer-by-layer assembly of graphene oxide was utilized to fabricate graphene based thin film in a scalable and highly reproducible way. It was found that optical transmittance and sheet resistance of the film decreases with an increase in number of LBL cycles in a reproducible way. The sheet resistance of LBL-assembled GO film improves by an order of magnitude at the same optical transparency due to more homogeneous coverage and better stacking of graphene flakes. Furthermore, we demonstrated the potential for a large-scale deposition of chemically derived graphene. INTRODUCTION Thin-film full spectrum silicon solar cells have attracted considerable interest as low-cost solar cells with high efficiency [1, 2]. Light management technology to effectively absorb more photons in a wide wavelength area is very important in order to realize thin-film solar cells. Graphene is one of the most attractive alternative materials for transparent conductive films (TCFs) because of its high electrical conductivity and optical transparency over a wide range of wavelengths [3-5]. Graphene is an atomically thin layer of carbon with superior electronic properties that has been a subject of intense study since its discovery in 2004 [6, 7]. A various kinds of graphene formation methods have been suggested up to now [8-10], one of the wellestablished methods is chemical exfoliation method via graphene oxide [11]. One of the greatest advantages of the chemical exfoliation method is that chemically derived graphene can be deposited or formed into films on any large area substrate. Ease of modification and/or functionalization of the graphene are also reasons why the chemical method is widely accepted [12]. A challenging problem of incorporating graphene into electronics is the exfoliation of graphite into individual sheets in a large-scale and controllable way. Recently, growth of waferscale graphene on silicon carbide as epitaxial growth and on copper as chemical vapor deposition has also been demonstrated [13, 14]. However, shortcomings of these methods are that these techniques requires sophist
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