Electrical and Optical Characterization of Cu4SnS4 and CdS:B Thin Films For Photovoltaic Applications
Oeba, Duke Ateyh
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Globally, there is a high demand for clean, sustainable and renewable energy for domestic and industrial use. Current photovoltaic cell technology relies heavily on crystalline silicon wafers. Silicon based solar cell are expensive because of their initial cost of production and they require complex deposition method. Due to these challenges, great research interest is now directed towards thin-film solar cells. In this research, chemical bath deposition (CBD) method is preferred because it is a reliable technique that can be applied for large scale production of photovoltaic cell. It is recommended for the preparation of thin film solar cells. Preparation of boron doped cadmium sulphide (CdS:B) and Cu4SnS4 thin films onto microscope glass slide was done using CBD technique. Boron doped cadmium sulphide (CdS:B) thin films were prepared, characterized and optimized for solar light trapping and used as a window layer. These layers were then characterized and optimized for electrical energy generation. These films were characterized using a four point probe to determine their surface sheet resistivity. Optical properties for the two films namely; reflectance and transmittance were measured using UV-VIS NIR 3700 spectrophotometer. Transmittance of CdS:B films varied between 70% and 81% for boron concentration range of 0.0 M to 0.06 M. It was noted that optical band gap varied from 2.96eV to 3.72eV, that is, band gap increased with increase of boron concentration. Cu4SnS4 thin films had transmittance below 45% appropriate for absorber layer of photovoltaic cell and a band gap of 1.46eV. Other related optical properties such as refractive index were obtained from simulation. Resistivity of Cu4SnS4 thin films decreased from 19.28 Ω-cm to 838 Ω-cm with increase in temperature whereas for CdS:B, resistivity decreased from 120 Ω-cm to 58Ω-cm with increase in boron concentration. The results were analyzed to determine optimum electrical and optical conditions that give Cu4SnS4 and CdS:B better qualities to fabricate a Cu4SnS4/ CdS:B photovoltaic cell. The fabricated Cu4SnS4/ CdS:B photovoltaic cell was characterized with results indicating that its cell properties like short circuit current (Isc) of 0.039A, open circuit voltage (Voc) of 0.4V, fill factor (FF) of 0.61 with conversion efficiency (η), of 1.59%. Based on the results obtained in this study, we conclude that the selected materials are suitable for fabrication of photovoltaic cell.