Effects Of Substrate Temperature Of Window Layer On The Performance Of Snxsey/Zno:Al P-N Junction Solar Cell

ABSTRACT

Various elements and compounds have been studied to fabricate thin film semiconductors for the solar cell applications. Apart from the materials used in the cell fabrication, the performance of solar cell also depends on the technique used and deposition parameters.In this research,the performance of the p-n junction solar cell is improved by depositing thin films at optimized deposition temperature. The optical and electrical behavior of thin films was analyzedundervariedchemical compositionanddepositionconditionsin order to optimizethemforanimprovedsolarcell. Zinc Oxide was doped with various percentages of Aluminum ranging from 0% to 10% by mass. Tin (Sn) and selenium (Se) metal samples were mixed in different ratios of increasing selenium. Deposition of both SnSe and ZnO:Al thin films on glass substrate was done by a method of evaporation using Edwards Auto 306 RF/DC Magnetron evaporation system under the following conditions; deposition temperature 500K, pressure of 3.5×10-5 millibars and a current of 3.5A. Transmittance and reflectance data in the range 300nm-1500nm was obtained using a double beam solid spec 3700 UV-VIS-NIR shimadzu spectrophotometer. Scout software was used to analyze the data to determine optical constants of the solar cell. Doping of 5% aluminium and a synthesized ratio of 1:1.0 for ZnO:Al and SnSe thin films respectively was obtained as the optimum values. The optimized Al doped ZnO was deposited at different deposition temperature ranging from 350K-550K. Transmittance percentage in the visible region was used to optimize deposition temperature and 510K was obtained as the optimum value. Band gap energies of optimized ZnO:Al and SnxSey was found to be 3.61±0.05eV and 1.37±0.05eV respectively. Electricalmeasurementsofthe thin films was donebyfourpoint probemethodin which measurements were obtainedusingKeithley 2400SourceMeterinterfacedwithacomputerusing LabViewprogram.The sheet resistivity for SnSe at a temperature of 295K was 22.95±0.05Ωcm while when annealed at 423K, a value of 19.27±0.05Ωcm was obtained. The sheet resistivity for ZnO:Al at room temperature was 32.24 Ωcm. The solar cell had a short circuit current (Isc) of 1.122mA/cm2, an open circuit voltage (Voc) of 0.61V, fill factor (FF) of 0.67 and conversion efficiency of 0.46% as calculated from the I-V characteristics.