Structural characterization of CdTe thin films developed on metallic substrates by close spaced sublimation

Cadmium telluride (CdTe) is one of the most investigated semiconductors for photovoltaic applications in the last four decades and is one of the most promising photovoltaic materials due to low-cost, high-efficiency, nearly optimum band gap (1.5 eV) for efficient photo conversion, high optical absorption coefficient (>104 cm−1) at band edge and the variety of deposition techniques available for its deposition as thin films. The close spaced sublimation (CSS) is one of the most promising methods to develop good quality CdTe films on large area substrates. There are various reports of the CdTe/CdS solar cells with efficiencies exceeding 16%, all prepared by CSS [1, 2]. In conventional solar cells, the CdTe is developed on the CdS window layer deposited on conducting glass substrates. But devices on glass substrates have the disadvantage of weight, inability to withstand high processing temperatures and are prone to damages. On the other hand devices on flexible metallic substrates can overcome all the above mentioned disadvantages of the glass based devices. Hence the development and characterization of CdTe on thin flexible metallic substrates are interesting. There are a number of reports regarding the characterization of CdTe thin films developed on CdS substrates by CSS, but practically no reports regarding the characterization of CdTe films developed on metallic substrates by CSS technique. We have deposited CdTe films on stainless steel by CSS at various source and substrate temperatures and the films were characterized using SEM and XRD. In this paper we are reporting the influence of the temperatures of substrate and source on the various structural parameters such as lattice parameter, grain size and stress. The investigations regarding the development of an interlayer between CdTe and the substrate are in progress and will be published in subsequent papers. The CSS system consists of a graphite reactor enclosed in a quartz tube. The tube was evacuated and