Enhanced current collection of CdTe solar cells in the long wavelength region by co-evaporation deposition CdSexTe1-x films

Abstract

Using a gradient band gap absorption layer to ensure high short-circuit current density is one of the key factors to prepare high-efficiency CdTe solar cells. CdSexTe1-x films with different selenium compositions were prepared by vacuum co-evaporation deposition technology. The effects of composition changes on the structure, morphology and properties of the films were studied. CdSexTe1-x films were incorporated into the CdTe solar cells with the structure of Glass/SnO2:F/CdS/CdSexTe1-x/CdTe/ZnTe:Cu/Au. The results show that the structure of CdSexTe1-x films is cubic when x is 0, 0.23 or 0.41, and while x is 0.61, 0.78 or 1 the structure is hexagonal. The minimum optical band gap is 1.40 eV with x = 0.41. It is found that in the long wavelength region, the cut-off edge of quantum efficiency curve depends on not only the thickness of CdSexTe1-x film with specific Se composition, but also the whole preparation process of solar cells. After using a 70 nm CdSe0.41Te0.59 film and 70 nm ZnTe:Cu back contact buffer layer, the cut-off edge of the long wavelength region can be reduced to 1.40 eV and the short-circuit current density of the device without antireflection layer reaches up to 28.8 mA/cm2.