Properties of zinc sulfur selenide deposited using a close-spaced sublimation method

The most extensively used buffer layer with p-CdTe thin film solar cells is n-CdS. However. up to 20% of the incident photons with energies greater than the energy bandgap of CdTe (E-g = 1.56 eV) are believed to be absorbed by the US layer (E-g = 2.42 eV). One solution to the problem is to use a wider energy bandgap window layer to permit more light to reach the junction, consequently improving the blue response of the cells. Some workers have now used ZnSe (E-g = 2.67 eV) to produce ZnSe/CdTe devices with efficiencies > 11%. Incorporating S into the ZnSe to form ZnSxSe1-x will widen the energy bandgap further, increasing the operating window of the solar cell and possibly improving the device interface. In this work, ZnSxSe1-x layers have been produced using a close space sublimation method. The results indicate excellent mixing of the anions to produce homogeneous alloys. as evidenced by the systematic shift of the energy bandgap with alloy composition. The X-ray diffraction data, scanning electron microscopy (SEM) data. and steep absorption edges in the transmittance data indicate the very good crystallinity of the layers produced. These results show the excellent promise of this method for making low cost, cadmium free, buffer layers for use in solar cells. (C) 2002 Elsevier Science B.V. All rights reserved.