Thin films of ZnO, CZTS (Cu 2 ZnSnS 4) and ZnO-CZTS were prepared by spray pyrolysis deposition (SPD). After spraying a precursor solution of ZnO directly onto fluorine-doped tin oxide (FTO) substrats, CZTS thin layers were sprayed onto layers of ZnO to forme a p-n junction. Some CZTS layers were directly spray onto fluorine-doped tin oxide substrats. ZnO is a wide band gap n-type material, consisting of abundant and nontoxic elements, and is thus expected to be a good substitute for CdS buffer layer in solar cells. In this paper, we report the study of CZTS and ZnO thin films synthesized by chemical spray pyrolysis (CSP) method. During the deposition of the ZnO thin films on the FTO substrats the number of sequences was varied from 20 to 40. The influence of the ZnO on the structural, optical, morphological and electrical properties of CZTS films was studied using various techniques. The X-ray diffraction studies showed the formation of kesterite (Cu 2 ZnSnS 4) phases with the peaks corresponding to (112), (220) and (312) planes. SEM study revealed a lack of uniformity of the surface of the CZTS layers sprayed onto the ZnO layers for a lower thickness of ZnO (FTO-ZnO20-CZTS). The band gap values of FTO-CZTS and FTO-ZnO-CZTS thin films were measured and found in the range 2.2-2.25 eV which are in good agreement with the results reported (2-2.2 eV). The morphological studies revealed the formation of some clusters randomly distributed on the film surface in the ZnO-containing layers, i.e. the FTO-ZnO20-CZTS and Finally, current-voltage measurements for different PV cells with maximum efficiency were carried out. A conversion efficiency (η) of 5.99% with fill factor (FF) = 18.8%, open circuit voltage (Voc) = 0.54 V, short circuit current density (Jsc) = 59 mA.cm2 were recorded through the FTO-ZnO40-CZTS thin film PV cell.
The use of the back surface field BSF within the thin film cells isn't elaborated in a current state of research. In this article we try to adapt it to the Cu(In,Ga)Se 2 thin film solar cells. The theoretical study is based on the resolution in one dimension of the equations which govern the behaviour of a photovoltaic cell. The spectrum used is the AM 1.5. The experimental method takes into account all physical phenomena which happen in the solar cell. The comparison of the macroscopic electric parameters of the two cells with BSF and without BSF enabled us to obtain a conversion efficiency of 21.95% for the cell with BSF whereas it is equal to 20.78% for the cell without BSF. The use of the BSF presents a broad maximum absorption band which extends from 0.4µm to 1µm through the study of the quantum efficiency of the cell. The spectral response of the layer reaches a value of 0.7A.W -1 for an incidental wavelength of approximately 1000nm which corresponds to the gap of the absorber of the solar cell of 1.2eV. The improvement of the thickness of the p+ CIGS up-doped, indicates an optimal thickness of 0.5.µm.We find for this thickness an open circuit voltage of 0.71V, a short-circuit current density of 37.409mA.cm -2 and a conversion efficiency of 21.95%. The optimization of the doping concentration acceptors of the p+ CIGS, shows that the optimal concentration corresponds to 10E18cm -3. We find with this acceptors density an open circuit voltage of 0.69V, a short circuit current density of 37.40mA.cm -2 and a conversion efficiency of 21.74%.
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