Fabrication and characterization of Molybdenum/Copper Zinc tin sulfide (CZTS)/Aluminum thin film structures

摘要

Recently, the quaternary semiconducting compound Copper Zinc Tin Sulfide (CZTS) has received increasing attention for applications in thin film solar cells because it offers optical and electronic properties that are comparable to those of the Ⅰ-Ⅱ-Ⅵ_2 materials (CIGS for example) while being composed of abundant and non-toxic elements. In this work CZTS thin films were prepared by the sol-gel process followed by spin coating on Mo-coated glass substrates. The precursor solution consisted of CuCl_2 (2M); ZnCl_2 (1.4M); SnCl_2 (1.3M); thiourea (8M) in a mixture of 70% Ethanol and 30% water. The solution was stirred at ambient temperature for 10 minutes. The CZTS thin films were then deposited from the as-prepared solution at a spinning speed of 4000 rpm for 30 s, followed by heat treatment at temperature of 90°C to 110°C in ambient air. This procedure was repeated three times and each time the film was cooled before the next layer was deposited. The final films were then annealed at 300 to 500°C in an argon atmosphere and in the absence of sulfur. X-ray Diffraction (XRD) studies revealed that the as-deposited films and those annealed in an Ar atmosphere, present the (112), (220), and (312) diffraction peaks that are characteristic of the kesterite phase. The Schottky barrier type structures were completed by depositing Al dots on the annealed CZTS films by thermal evaporation at a vacuum of 4×10~(-6) mbar. The Ⅰ-Ⅴ characteristics these structures showed a rectifying behavior. In addition, both their conductance and capacitance varied with applied voltage and frequency. These measurements are used to analyze and discuss the current transport mechanisms in these structures.