Enhanced electrical properties of Te-enriched ZnTe thin films for buffer layer in solar cell

Zinc Telluride (ZnTe) powder of 99.9% purity was used to deposit ZnTe thin films on ultra-sonically cleaned slides of glass. A locally manufactured Closed Space Sublimation (CSS) technique was used to deposit these thin films. As-deposited ZnTe thin films were further exposed to tellurium (Te) for different deposition times under high vacuum. Annealing was carried out after the deposition of Tellurium (Te) on as-deposited ZnTe thin films for diffusion of Te into ZnTe thin films. Cubic phases were found before and after enrichment of Te into as-deposited ZnTe thin films via X-ray Diffraction (XRD) studies. Preferred orientation was [111] and the crystallite size increased after enrichment of Te. The surface morphology was studied using scanning electron microscopy (SEM) which confirmed that grain sizes significantly increased after the enrichment of Te into ZnTe thin films. Energy dispersive X-rays (EDX) confirmed the elemental composition of zinc (Zn) and tellurium (Te). The transmittance decreased after the enrichment of Te into ZnTe thin films. A small change in energy band gap was calculated using Tauc relation. Hall measurement was carried out to study the electrical behavior of Te-enriched ZnTe thin films and found that electrical resistivity of as-deposited ZnTe thin films was of the order of 10⁶ Ω-cm. The electrical resistivity reduced to 10⁴ Ω-cm after Te enrichment. X-rays photoelectron spectroscopy (XPS) study was carried out to check the chemical bonding and states before and after Te-enrichment. Te-enriched ZnTe thin films showed better properties and found suitable for buffer layer of II generation solar cells.