Optical and electrical characterization of ZnS:Sn - CuO thin films for solar cell application
Wanjala, Khisa Simeon
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During the last decades, the energy problem on the planet has been growing steadily. Reasons being rapid increase in world population and need for improved living standards. This has led to increase fossil fuel prices due to more expensive and more risky fossil fuel depletion. To overcome these problems it is necessary to change the energy infrastructure _within this century. The higher energy consumption can be compensated by an increase in usage of solar power. This work is devoted to the study of emerging area of thin films for solar cells regarding development of p-n junctions for solar cell applications. In this study, CuO and Sn doped ZnS thin films were used because of their promising properties required in solar cell fabrication. ZnS:Sn thin films were prepared using a Chemical Bath Deposition (CBD) technique at a pH of9. CuO thin films were prepared using sputtering technique to optimize deposition power for CuO films that can be applied in solar cell fabrication. This was done by use of Edwards auto 306 coating unit. The chamber pressure was maintained at 9.0 x 1O-3mbars during the film deposition. The deposited films were characterized for optical and electrical properties. The optical measurements were done using UV -VIS-NIR spectrophotometer Solid State 3700 DUV and the transmittance spectra data obtained was analyzed using the SCOUT software. The transmittance for copper oxide ranged between 55% to 70% and that of ZnS:Sn was above 79%. The band gap of CuO and ZnS:Sn thin films were deduced to be within the range 1.20-2.91eV and 3.91-4.12 eV respectively. The value of resistivity for ZnS:Sn was between 96-120 Ocm while that of copper oxide was found to be between 37-1190cm as obtained with a four point probe .. The CuO/ZnS:Sn p-n junction solar cell was also fabricated by double depositing the optimized films on a microscope glass slide. The current - voltage (I-V) characterization of the p-n junction diode was done using a solar cell simulator and the data obtained was used to calculate solar cell parameters; open circuit voltage Voc= 461. 12mV, FF = 0.6312 and the short circuit current Isc= 2.052 mA /cm2. The resulting solar cell efficiency 11 of 0.597 % was obtained.