Single Step Electrodeposition of CZTS Absorber Layer for Solar Cells Application

Abstract

Nowadays, one of the most critical issues in photovoltaic (PV) industry is the fabrication of an efficient and low cost solar cells. The solar energy have to be more efficient and cost effective than other electricity sources in order to be a major source of electricity. Different types of photovoltaic materials have been developed over the past century and the latest technology is based on thin film solar cells. Copper indium gallium selenide (CIGS) thin film based solar cells have achieved more than 20% power conversion efficiency. However, these materials are toxic, rare and expensive. Copper zinc tin sulfide (CZTS) is a very promising material and a good alternative for CIGS thin film. CZTS materials are cheap, non-toxic and abundant. Also, It has an ideal band gap of 1.5 eV and a high absorption coefficient. Single step electrodeposition technique was used to deposit CZTS thin film on fluorine doped tin oxide (FTO) coated glass substrate. In order to identify the suitable deposition potential, a set of CZTS thin films were deposited at different potentials. The used potentials were -1.10 V, -1.20 V, -1.25 V, -1.30 V, and -1.35 V ( vs. Ag/AgCl). XRD and Raman analysis were used to confirm the presence of CZTS kesterite phase. There was a dependence for the intensity and FWHM of the (112) planes peaks which affect the crystallite size. The sample deposited at -1.35 V had the highest crystal size and the best crystalline quality. The EDS and XPS measurements were performed and the best stoichiometry was achieved in the sample deposited at -1.35 V. The influence of sulfur amount in the sulfurization process on the CZTS thin films was also investigated. So, a set of CZTS films was electrodiposited using -1.35 V and sulfurized using 5 mg, 15 mg, 25 mg, 35 mg, and 50 mg of sulfur powder. The best CZTS thin film stoichiometry and crystalline quality was achieved using 35 mg sulfur according to XRD, Raman and EDS analyses. Uv-visible and Photoluminescence (PL) measurements were used to study the optical properties of the electrodeposited films. The sample electrodeposited at -1.35 V using 35 mg sulfur exhibited a 1.50 eV optical band gap and 104 cm-1 absorption coefficient. These results confirm the suitability of these films to be utilized as absorber layers in thin film solar cell structures.