Elaboration et étude de structures à base de couches minces de ZnO et de chalcogénures (CIS, CZTS) pour des applications photovoltaïques

Abstract

Among the most promising quaternary semiconductors for thin film solar cells fabrication is the Cu2ZnSnS4 (CZTS) material. Our choice in this thesis, to elaborate the CZTS thin films was related to the spray pyrolysis method. This choice was based on low cost thin film process deposition with material properties satisfying the photovoltaic criteria. The effect of some experimental parameters on the properties of layers was studied, such as, the copper concentration, deposition time, the temperature of the substrate and the doping by Au nanoparticles. After preparation, films were subjected to a various characterizations structural, morphological, optical and electrical. The structural characterization present the Cu2ZnSnS4 under its kësterite structure showing a high degree of preferred orientation towards the (112) direction and for a copper concentration of 0.010M, indicating that the film has a single dominant phase CZTS. The optical gap values vary from 1.2 to 1.69 eV suggesting that CZTS thin films can be a good candidate as absorber layer for thin films solar cells. The resulting films of the copper concentration 0.010M are rich in Zn and poor in Cu. This composition is desired to improve the efficiency of solar cells based on CZTS. In other hand, the films doped with Au nanoparticles reduces the formation of secondary phases, increases the conductivity of the layer and improved the values of the optical gap for use in solar cells. I-V characteristics of heterostructures CZTS/CdS/FTO and CZTS/ZnS/FTO made from films prepared according to the studied experimental conditions. The results show relatively low values of characteristics: short circuit current density, open circuit voltage and efficiency. The results are caused by the influence of several parameters, the high values of resistance series, saturation current and the interface states. From the thermal activation energy of the saturation current we deduced that the reverse current is controlled by thermal emission through the barrier height rather than by tunneling through the defects localized in the band gap. The Au/CZTS/CdS/FTO heterojunction exhibits a photovoltaic effect but with a poor efficiency (0.26%).