Atomic Layer Deposition of Indium Sulfide Layers for Copper Indium Gallium Diselenide Solar Cells
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MRS Proceeding, Donsanti et al. Symposium H poster H8.20 Atomic Layer Deposition of Indium Sulfide Layers for Copper Indium Gallium Diselenide Solar Cells F. Donsanti, B. Weinberger, P. Cowache, M. C. Bernard# and D. Lincot* Laboratoire d’Electrochimie et de Chimie Analytique (UMR CNRS 7575) Ecole Nationale Supérieure de Chimie de Paris 11 rue Pierre et Marie Curie 75231, Paris cedex 05, France # Groupe de Physique des Liquides et Electrochimie (UPR CNRS 15), Université Pierre et Marie Curie, 4 place Jussieu, 75232 Paris cedex 05, France * [email protected]
ABSTRACT Growth and properties of indium sulfide layers (< 300 nm) prepared by atomic layer deposition (ALD) have been studied. Growth rate of about 0.6 A per cycle has been measured for films deposited at 160°C from indium acetylacetonate and hydrogen sulfide precursors. The films are crystalline with the β modification. They possess high band gap values (2.7-2.8 eV) which are related to small grain sizes (3-4 nm) through quantum size effects. Electrical properties have been addressed using the semiconductor electrolyte junction. They are n type with a doping level around 1016 cm-3 and possess a good blocking behavior under reverse bias. The flat band potential is close to -1 V vs MSE. These figures are close to those measured under similar conditions with CdS CBD buffer layers and could explain the good cell performances obtained with ALD In2S3. Key words: photovoltaics, indium sulfide, atomic layer deposition, electrolyte junction, copper indium diselenide INTRODUCTION High efficiency copper indium gallium diselenide (CIGS) solar cells present the following structure CIGS/buffer layer/ZnO where the buffer layer is generally a thin CdS layer (30-50 nm) deposited chemically from an aqueous solution. The presence of this buffer layer is essential to achieve high performances and reproducibility. Many efforts are currently paid to replace the CdS by other compounds [1,2] like ZnSe, ZnS and In2S3 mainly. When prepared from aqueous solutions, these compounds frequently contain a certain amount of oxygen as hydroxyl groups. Deposition from the vapor phase, including also zinc oxide, is also considered with the expected potential advantage of allowing complete vacuum in line processing for cell preparation. In this work we investigate the deposition of indium sulfide buffer layers by Atomic Layer Chemical Vapor Deposition (ALCVD). In previous papers an efficiency of 13.5% was reported using a 30 nm thick indium sulfide layer and some properties of these layers were presented [2,3]. In the present paper the characteristics of these layers are further studied and discussed, including compositional, structural and preliminary electrical aspects.
H8.20.1
MRS Proceeding, Donsanti et al. Symposium H poster H8.20 EXPERIMENTAL Depositions have been carried out in an ALD reactor F120 from ASM-Microchemistry. The indium precursor was indium acetylacetonate, In(CH3COCHCOCH3)3, indicated as In(acac)3. The sulfur precursor was H2S. Depositions were usually carried out with
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