Cadmium sulphide thin films for photovoltaic applications

Problem: Solar cell efficiency improvement is one of the most important of today's goals. TCO/A2B6-based multilayer thin film structures are widely used as second-generation solar cells. CdS thin film as a direct band gap n-type semiconductor is suitable for window layer of CdS/CdTe solar cells. The aim of this work is studying the influence of the substrate temperature and the density of laser energy on phase composition, microstructure and optical properties of pulsed laser deposited CdS thin films. Methodology: Pulsed laser deposition method (PLD) is suitable for the fabrication of high-quality thin films at lower temperatures in comparison with other physical vapor deposition methods. The method also gives an ability to control the properties of obtained films, such as substrate temperature and laser energy density on target. Results and discussion: CdS thin films on glass substrates were obtained using pulsed laser deposition (PLD) method. From XRD data it is clear that CdS films include two phases: cubic phase with sphalerite structure and hexagonal phase with wurtzite structure. The increase of the substrate temperature up to 500$^o$С leads to the formation of hexagonal phase, to the crystallite size growth and the appearing of visible grain boundaries. The increase of the laser energy density from J = 1.5 J/cm$^2$ to J= 5.5 J/cm$^2$ also leads to phase composition change and to the increase of the relative content of hexagonal phase. Hence the PLD method gives an ability to control physical properties of CdS by varying the substrate temperature (Ts) and the energy density (J). Practical importance: PLD method allows to obtain multilayer thin film structures for photovoltaic applications. An ability to control the physical properties of n-type semiconductor thin films (CdS) by varying the PLD parameters such as substrate temperature (Ts) and the energy density (J) has been studied.