Substrate temperature dependent structural, optical, morphology and electrical properties of RF sputtered CdTe thin films for solar cell application

Abstract

In this work, we have studied the influence of substrate temperature on structural, morphology optical, and electrical properties of CdTe thin films deposited by RF magnetron sputtering. Films were analyzed by using variety of techniques such as low angle X-ray Diffraction, UV-Visible spectroscopy, Raman spectroscopy, Field emission scanning electron microscopy (FE-SEM), Energy-dispersive X-ray spectroscopy (EDAX) Hall Measurement etc. Low angle XRD analysis showed that CdTe films are polycrystalline and has cubic structure with preferred orientation is along (111) direction. Raman scattering studies revealed the presence of single phase CdTe over the entire range of substrate temperature studied. The FE-SEM analysis showed that CdTe growth process occurred predominantly by grain growth and not through the layerby-layer mode. Compositional analysis carried out using EDAX suggests that CdTe films deposited at low substrate temperatures are Te rich and that at higher temperatures is Cd rich. Electrical resistivity of CdTe films decreases with increase in substrate temperature and whereas positive increase in Hall coefficient suggests as-deposited CdTe films are p-type. The UV-Visible spectroscopy analysis showed that the band gap increases from 1.47 to 1.51 eV when the substrate temperature increased from 50 to 300°C. Such optimum band gap CdTe can be use as absorber material in photovoltaic applications like the CdS/ CdTe and ZnO/CdTe solar cells.

Regulation of Substrate-Target Distance on the Microstructural, Optical and Electrical Properties of CdTe Films by Magnetron Sputtering

“…In recent years, silicon (Si) has been considered as the most important material for preparing film-form solar cells, due to its well-established preparation process and its theoretical conversion efficiency of Si-based solar cells being approximately 25% [1,2]. However, Si films exhibit low absorptivity in the range of 0.5–1.0 μm, and improving the absorptive capacity requires thicker films which would increase costs [3]. Furthermore, the energy band gap of Si films is only 1.12 eV, which cannot completely cover the radiation spectrum of sunlight [4].…”