Comparative study of the structural and optical properties of CIS films prepared by RFmagnetron sputtering and selenizat
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Comparative study of the structural and optical properties of CIS films prepared by RFmagnetron sputtering and selenization of elemental layers António F. Cunha, M.M. Pereira de Azevedo, Ricardo J.O. Ferrão, A.A.C.S. Lourenço and Claude Boemare Departamento de Física da Universidade de Aveiro, Campus Universitário de Santiago, 3810193 Aveiro, Portugal ABSTRACT We report on a study where the properties of films obtained by RF-magnetron sputtering and by Selenization of elemental precursor layers are analysed by Raman scattering, x-ray diffraction and optical measurements. Three routes were followed to prepare CIS films on glass. CIS type-I was prepared by selenization at various temperatures, CIS type-II was prepared by RF-magnetron sputtering on room temperature substrate followed by annealing at 450ºC in air for 10 min and CIS type-III was prepared by RF-magnetron sputtering on a substrate at a temperature ranging from 200ºC up to 500ºC with a post-deposition annealing in the same conditions as for CIS type-II. Correlating the results from x-ray diffraction with the Raman scattering and optical measurements it was possible to establish unequivocally the formation of CIS with the chalcopyrite structure for CIS type-I at 400ºC. Through the same procedure it was possible to establish a way to produce CIS type-II with the chalcopyrite structure. A high density of defects was inferred from the transmission results. Finally the growth dynamics of CIS typeIII was studied. It was observed a structural/compositional transition around substrate temperature of 300ºC. It was observed that all the films had a sphalerite structure even for the highest substrate temperatures. It was establish the need for a post-deposition annealing to obtain CIS type-III with the chalcopyrite structure. The Raman scattering was found to be a very sensitive technique that allowed us to uncover a difference in the CIS type-I and II with the chalcopyrite structure. INTRODUCTION Solar cells based on CuInGaSe2 (CIGS) grown by co-evaporation have been demonstrated in laboratory with efficiency around 18% and high material stability hence these are promising materials for this application [1]. Growth methods better suited to large-scale production are, currently, object of intense research worldwide. Various methods are being exploited namely electrodeposition, spray pyrolysis, selenization, RF-magnetron sputtering [2]. In this work we carry out a comparative study of the structural and optical properties of films grown by the latter two techniques. EXPERIMENTAL DETAILS The CuInSe2 (CIS) films studied in this work were prepared by selenization of Cu/In/Cu elemental precursor layers at temperatures between 199ºC and 400ºC in an atmosphere of Ar/Se, at a pressure of 4x10-1mbar for 1 hour (CIS type-I) and by RF-magnetron sputtering (13.56MHz) at substrate temperatures ranging from room temperature up to 500ºC (CIS type-II,III). In the selenization method, the precursor layers were deposited by RF-magnetron sputtering on soda lime glass slides ultrasonical
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