Date Published: June 01, 2016
Publisher: International Union of Crystallography
Author(s): Paul Pistor, Jose M. Merino Álvarez, Máximo León, Marco di Michiel, Susan Schorr, Reiner Klenk, Sebastian Lehmann.
We report on the high-resolution structure analysis of In2S3 powder with monochromatic synchrotron light in the temperature range between 300 and 1300 K. Three modifications could be identified with the two phase transitions taking place at 717 K and above 1049 K. Crystal structure parameters and their temperature dependence for all three phases were extracted from the diffraction data by Rietveld refinement.
In2S3 is a widegap semiconductor with high photoconductive and photoluminescent properties, which makes it a promising material for optoelectronic applications (Shazly et al., 1998 ▸). Most prominently, its potential application as a buffer layer in chalcopyrite solar cells has triggered an increased research effort in its fundamental materials properties (e.g. crystal structure, optical properties, electronic bandstructure etc.) as well as in deposition technology. The compatibility with various thin film deposition methods make it a versatile alternative to the commonly applied CdS buffer layer. Among the compatible deposition methods, atomic layer deposition (Naghavi et al., 2003 ▸), the ion layer gas reaction (ILGAR) method (Sáez-Araoz et al., 2012 ▸), spray pyrolisis (John et al., 2005 ▸), sputtering (Hariskos et al., 2005 ▸) and evaporation (Strohm et al., 2005 ▸) have been successfully applied. The interested reader is referred here to the excellent review by Barreau (2009 ▸) on the role of In2S3 in the world of photovoltaics. Various reports on In2S3 buffer layers correlate deposition process parameters with crystallographic properties (Rao & Kumar, 2012 ▸; Larina et al., 2004 ▸; Yoosuf & Jayaraj, 2005 ▸) and ultimately with final solar cell device parameters (Naghavi et al., 2003 ▸; Pistor, Caballero et al., 2009 ▸).
In this section we will briefly discuss the crystal structure of the three modifications and how the different modifications may impact the application of In2S3 in thin film solar cells.
We provide a detailed crystal structure analysis of In2S3 over the entire temperature range from room temperature up to close to the melting point covering the three modifications β-In2S3, α-In2S3 and γ-In2S3. With this, we contribute to the comprehensive understanding of the different phases existent and their interdependence. The high-temperature phase γ-In2S3 has been analysed and refined for the first time in the pure phase. Finally we show how the detailed knowledge of the phase diagram and the different In2S3 modifications might have a direct impact on the technological use of In2S3 in applications such as buffer layer deposition in thin film solar cell production.