Characterization of CuᵪOᵧ - ZnO:Sn P-N Junction for solar cell applications
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Date
2014-05-02
Authors
Omayio, Enock Osoro
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Abstract
The Cu.O, - ZnO:Sn p-n junction solar cell has been fabricated in steps. Cu.O, and
ZnO:Sn thin films were first deposited by reactive de magnetron sputtering and reactive
evaporation techniques respectively using Edwards Auto 306 vacuum coater system
.Cu.O, films were deposited at oxygen flow rates between 5-30 seem, ZnO:Sn films were
deposited with Sn doping concentrations reaching 6%. Transmittance of ZnO:Sn films
was above 70% for Sn doping less than 5% whereas reflectance was below 40% within
the visible range. For Cu.O, films, transmittance increased with increase in wavelength
and reflectance was below 35 % within the visible range. From simulation of optical
spectra of films using scout software absorption coefficient, refractive index and optical
band gap of thin films were obtained. For both Cu.O, and ZnO:Sn films, absorption
coefficient decreases with increase in wavelength of incident radiation. Optical band gap
of CuxOy films increased with increase in oxygen flow rate to a maximum of 2.64 eV at
10 seem of O2 flow after which it started to decrease. For ZnO:Sn films, optical band gap
decreased with increase in Sn doping to a minimum of 2.48 eV at 4% Sn doping after
which it started to increase with increase in Sn doping. Electrical resistivity of Cu.O,
films increased slightly with increase in 02 flow whereas for ZnO:Sn film's resistivity
decreased with increase in Sn doping concentration with minimum resistivity of
21.1 ncm. Solar cell was fabricated on transparent glass slide from 250nm thick p-type
Cu.O, film deposited at oxygen flow of 5 seem and 140 nm thick n-type ZnO:Sn film
deposited with 2% Sn doping concentration. I-V characteristics of the solar cell were
measured by Keithley 2400 sourcemeter interfaced with computer running labview
program. It had Voc of 480 mV and fill factor of 0.63 which is higher than those of other
cells in literature. The fabricated solar cell had conversion efficiency of 0.232%.
Description
Department of Physics, 88 p. The TK 2960 .O4 2011
Keywords
Solar cells, Solar energy