Enhancing the performance of thin film CdS/PbS photovoltaic solar cells

This work investigates dependence of the short-circuit current density, open-circuit voltage, fill factor and efficiency of a thin film CdS/PbS solar cell on thickness of transparent conductive oxide (TCO) layer, thickness of window layer (CdS), concentration of uncompensated acceptors (width of space-charge region), carrier lifetime in PbS and the reflectivity from metallic back contact. The effect of optical losses, front and rear recombination losses as well as the recombination losses on space-charge region are also considered in this study. As a result, by thinning the front contact layer indium tin oxide from 400 to 100nm and window layer (CdS) from 200 to 100nm it is possible to reduce the optical losses from 32 to 20%. The effect of electron lifetime on the internal and external quantum efficiency can be neglected at high width of the space-charge region. The maximum current density of 18.4mA/cm(2) is achieved at wide space-charge region (concentration of uncompensated acceptors=10(15)cm(-3)) and the longest lifetime (tau(n)=10(-6) s) where the optical and recombination losses are about 55%. The maximum efficiency of 5.17%, maximum open-circuit voltage of 417mV and approximately fixed fill factor of 74% are yielded at optimum conditions such as: electron lifetime=10(-6) s; concentration of uncompensated acceptors=10(16)cm(-3); thickness of TCO=100nm; thickness of CdS=100nm; velocity of surface and rear recombination=10(7)cm/s and thickness of absorber layer=3 mu m. When the reflectance from the back contact is 100%, the cell parameters improve and the cell efficiency records a value of 6.1% under the above conditions.