Title: ﾇﾐﾀﾇﾎﾊ ﾎﾔﾎﾐﾌﾋﾅﾍﾍﾟ ﾒﾅﾇ ﾄﾎﾏﾎﾂｲﾄｲ
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Nanoscale Physics

The numerical simulation of graded band gap CdSeTe thin film solar cell 
Danylov A.B., Ilchuk H.A., Petrus R.Yu.
Lviv Polytechnic National University, S. Bandera Str., 12, Lviv-79013, Ukraine.
E-mail: andriy.b.danylov@lpnu.ua

Cadmium telluride is widely used in the solar cell technology. The band gap of the compound is in good agreement with solar radiation spectrum. Throughout the visible light range, CdTe is characterized by high values of the absorption coefficient. However, the efficiency of CdTe use in photovoltaics is influenced by a significant surface recombination coefficient and a rather short lifetime of the carriers.
The band gap of CdSe_yTe_1-y solid solution changes nonlinearly with the change in selenium content. Pure CdSe has a band gap of about 1.7 eV. As the selenium content decreases, the band gap decreases to approximately 1.4 eV at y = 0.5-0.6, and then increases to 1.45 eV for CdTe.
The use of graded band-gap ternary compound with variable concentration of selenium can be implemented in different ways:
It is possible to form a layer on the surface with a wide band gap, and then gradually reducing the selenium content with the film depth, we will get a structure with a built-in electric field, which, on the one hand, will more effectively separate charge carriers directed by the field through p-n junction and the effect of surface recombination is reduced due to the generation of carriers not on the surface but in the structure bulk.
Reducing the band gap reduces the open circuit voltage and fill factor. However, narrow band allows a more efficient use of the long-wavelength range of the solar spectrum. As a result, the short-circuit current increases.
The dependence of the coordinate profiles of the distribution of minor charge carriers is investigated and the efficiency of solar cells at different profiles of the band gap at different contents of selenium in the ternary compound is determined. Conclusions are made about the optimal structure parameters that allow achieving maximum solar cell efficiencies.