Deposition and characterization of CZTS thin film for solar cell applications

(CZTS) is a p-type semiconductor material consisting of four elements that are abundant and friendly to the environment. In addition, it has a high light absorption coefficient and band gap value (1.5 eV) which is suitable to absorb the maximum number of photons from the sun's radiation. These favorable properties make it an excellent alternative material for the absorbance layer of solar cell applications. In this work, Cu2ZnSnS4 (CZTS) thin films were successfully deposited on glass/FTO substrates using a hand spray pyrolysis technique at a stoichiometric composition ratio of (2:1:1:4). They were optimized in the manner of best substrate temperature to produce crystalline CZTS film. To see the effect of annealing temperatures on the CZTS, thin films were annealed at different temperatures (250, 300, 350, and 400 ◦C) under atmospheric conditions and, it was observed that the crystal grain size increased with increasing annealing temperature and the ideal annealing temperature was determined to be 400 ◦C. To produce Cu-poor films that are more suitable for solar cell applications; the structural, optical, and electrical properties of the CZTS films were evaluated by using XRD, SEM, EDS, UV-Vis, and I-V measurements. The result revealed that the best substrate temperature is 400 ◦C and the EDS result proved to be CZTS thin film exhibiting poor-Sn behavior. FTO/CZTS/CdS/ZnO devices were produced using these films as an absorber layer and characterized by current-voltage (I-V) measurements under dark and AM1 light conditions. The effect of Cu, Zn, and Sn concentration on CZTS thin film was also studied. A substrate temperature of 400 ◦C and an annealing temperature at 400 ◦C applied for a copper-poor zinc-rich non-stoichiometric ratio of (1.6:0.9:0.8:1.2) led to the success of the synthesis of CZTS thin film. The FTO/CZTS/CdS/ZnO device was successfully produced by depositing CZTS, CdS, and ZnO thin film on a glass FTO substrate and characterized electrically. This device gave a power conversion efficiency of 0.02 % with the non-stoichiometric ratio of Cu/Zn + Sn = 0.79 and Zn/Sn = 1.23. Experimentally, it was clarified for the first time that a device structure of FTO/CZTS/CdS/ZnO can be run as a solar cell by using low-cost material and a fully spray pyrolysis deposition technique which is the aim of this thesis. Keywords: CZTS, Stichometry, Spray pyrolysis, FTO, Solar cell.