Copper Indium Diselenide thin films using a hybrid method of chemical bath deposition and thermal evaporation
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Copper Indium Diselenide thin films using a hybrid method of chemical bath deposition and thermal evaporation R. Ernesto Ornelas A1, Sadasivan Shaji1,2, Omar Arato1, David Avellaneda1, Alan Castillo1, Tushar Kanti Das Roy1 and Bindu Krishnan1,2 1 Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, México 2
CIIDIT- Universidad Autónoma de Nuevo León, Apodaca, Nuevo León, México.
ABSTRACT Copper indium diselenide (CIS) based solar cells are one among the promising thin film solar cells. Most of the processes reported for the preparation of CIS directly or indirectly involve Se vapor or H2Se gases which are extremely toxic to health and environment. In this work, we report the preparation of CIS thin films by stacked layers of Glass/In/Se/Cu2Se and Glass/In/Se/Cu2Se/Se. For this, first indium (In) thin film was thermally evaporated on glass substrate on which selenium (Se) and copper selenide (Cu2Se) thin films were deposited sequentially by chemical bath deposition. Selenium thin films were grown from an aqueous solution containing Na2SeSO3 and CH3COOH at room temperature, triple deposition for 7, 7 and 10 min from consecutive baths. Copper selenide thin films were deposited at 35 °C for 1 hour from an aqueous bath containing CuSO4, Na2SeSO3 and NH4OH. Analysis of the X-ray diffraction patterns of the thin films formed at 400 °C from the precursor layer containing extra selenium layer showed the presence of chalcopyrite CuInSe2, without any secondary phase. Morphology of all the samples was analyzed using Scanning Electron Microscopy. Optical band gap was evaluated from the UV-Visible absorption spectra of these films and the values were 1.1 eV and 1 eV respectively for CIS thin films formed at 400 °C from the selenium deficient and selenium rich precursor layers. Electrical characterizations were done using photocurrent measurements. Thus preparation of a CuInSe2 absorber material by a non-toxic selenization process may open up a low cost technique for the fabrication of CIS based solar cells. INTRODUCTION CuInSe2 (CIS) belongs to I-III-VI2 group of semiconductor materials and crystallize with tetragonal chalcopyrite structure [1], and is one of the most promising absorbing materials for thin film solar cells, due to high absorption coefficient and direct band gap [2]. CIS thin films have been prepared by several methods such as elemental thermal evaporation [3], binaries compounds thermal evaporation [4], RF sputtering [5], co-sputtering of metallic precursors and selenization [6], pulse laser deposition (PLD) [7], metal organic chemical vapor deposition (MOCVD) [8], electrodeposition [9], chemical bath deposition (CBD) [10] and SILAR [11]. Most of the processes involve heating the precursor layers or a post-deposition treatment in Se vapor/H2Se gas which are extremely toxic to health and environment. Formation of CIS thin films by heating stacked layers of chemically deposited selenium and vacuum deposited In and Cu was known [12]. Further, use of
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