Electrical characteristics of thin-film CdS/CdMgTe heterostructure for tandem solar cells

• I–V characteristics of CdS/Cd1−xMgxTe solar cells are described well by the Sah–Noyce–Shockley theory.
• Comparison of the calculated and measured results allowed determining the parameters of the material.
• A new method to determine the barrier height in heterostructure with a good accuracy has been used.
• The theory describes well the I–V characteristics of some solar cells, which turned out to be shunted.
• High resistivity of the absorber layer causes low barrier height and unacceptable electrical losses.

Charge transport mechanism in thin-film CdS/Cd1−xMgxTe (x = 0.08) heterostructure are investigated. It is shown that the measured I–V characteristics and their temperature dependence are described well in terms of the Sah–Noyce–Shockley theory of generation–recombination in the diode space-charge region. A comparison of the experimental data with the theoretical results allowed determining the material and diode parameters such as the resistivity and hole density in the valence band of the film, the energy of the Fermi level and the barrier height at the interface, the lifetimes of charge carriers and the ionization energy of the generation–recombination center. It is also shown that low resistivity of the Cd1−xMgxTe absorber layer causes too low barrier height in the heterostructure and unacceptably high electrical losses in the solar cell.