Cu-In and Cu-Zn-Sn Films as Precursors for Production of CuInSe 2 and Cu 2 ZnSnSe 4 Thin Films
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1165-M05-40
Cu-In and Cu-Zn-Sn Films as Precursors for Production of CuInSe2 and Cu2ZnSnSe4 Thin Films
O. Volobujeva, E. Mellikov, J. Raudoja, S.Bereznev, M. Pilvet Department of Materials Science, Tallinn University of Technology, Ehitajate tee 5, Tallinn, 19086, Estonia
ABSTRACT The single sputtered Cu-In precursor layers were characterized by bi-layer surface structure in which island-type crystals were formed in a small-crystalline matrix layer. The elemental composition of the island-type crystals corresponds to the compound CuIn2 and the matrix (area) consists of copper-rich Cu11In9 phase. The surface morphology of sequentially evaporated CuZn-Sn precursor layers is determined by the deposition order of stacked consistent metal layers. Precursor Mo-Cu-Zn-Sn films exhibit a well-formed “mesa-like” structure of the surface in which larger crystals (about 1,5 µm) are located on a “small-crystalline” valley. For films with other sequences of metallic layers, the mesa like structure is not so well exposed and well formed flat precursor layers were produced replacing separate metallic Cu and Sn layers with Cu/Sn alloy layer. Selenization of both Cu-In and Cu-Zn-Sn precursor layers begins with the formation of binary Cu-selenides with compositions varying with the temperature. At temperatures higher than 3700C the selenization of Cu-In results in single-phase CuInSe2 films in contrast to the selenization of Cu-Zn-Sn films that results always in multi-phase films consisting of high quality Cu2ZnSnSe4 crystals and of separate small-crystalline phase of ZnSe.
INTRODUCTION An affordable electricity supply is essential to meet basic human needs. With forecasts of over 30 TW of new power needed by 2050, the carbon emissions associated with the expansion, or even continuation, of current fossil-fuel-based electricity generation would make maintaining atmospheric CO2 concentrations much higher than their current levels [1]. Solar photovoltaics (PV) are frequently cited as a promising but an economically unrealistic large-scale supply option for a low-carbon future [2]. Photovoltaics has enjoyed extraordinary growth during the last few years with overall growth rates between 30% and 40%, making further increase of production facilities a very attractive investment. Up to now, CdTe, CuInSe2 and its quartenary compounds are the materials most widely investigated and used in thin film solar cell applications. Devices based on CuInGaSe2 have yielded efficiencies of 19.9 %. In spite of great progress made in cheaper technologies for thin film solar cell production, problems connected with materials suitable for cheap thin film technologies still remain unsolved. The reasons lie mainly in the availability and limits of the materials used. Unconventional solar cell materials that are as abundant as silicon but much less
costly could substantially reduce the cost of solar photovoltaics. Cu2ZnSnS4, Cu2ZnSnSe4 (CZTS, CZTSe) are believed to be the most promising absorber material in a thin film solar cell because of its excellent
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