Requirements imposed on the electrical properties of the absorber layer in CdTe-based solar cells

The requirements for minimizing the electric losses in the CdTe layer in CdS/CdTe thin-film solar cells are discussed. It is shown that for achieving the total absorption of the radiation and to avoid electrical losses, the separation between Fermi level and the valance band should not be more than 0.3 eV. In order to fix the Fermi level near the valence band, it is necessary to dope with acceptor impurities which can introduce shallow level in the band gap with a concentration considerably exceeding the concentration of native impurities and defects (1015–1016 cm−3). Taking into account the fact that the location of the Fermi level in the bandgap of a semiconductor depends on the degree of compensation, the energy of ionization of the impurity should not be greater than 0.05–0.15 eV.