Spectroscopic Ellipsometry Studies of CdS:O Layers for Solar Cells

Abstract

This work reports the results of spectroscopic ellipsometry study of CdS thin films, deposited on glass substrates in the presence of oxygen at room temperature by rf sputtering. The data acquisition, together with the subsequent linear regression analysis to restore dielectric function has been performed over the photon energy range 1.5–5.0 eV. The obtained oxygen-free CdS films and reference bulk CdS have been found to be very much the same regarding their dielectric function spectra. On the other hand, blue-shift of the main structures in dielectric function has been observed for CdS:O films deposited at 5% value of O/Ar ratio. In spite of the broadening taking place on a par with the shift, the last turns out to be so large that provides transparency of CdS:O thin films in a spectral range above the energy gap of CdS. The obtained results allow to considering CdS:O as an improved window-layer material for solar cell application.

The effects of high temperature processing on the structural and optical properties of oxygenated CdS window layers in CdTe solar cells

“…2 It has been reported that the incorporation of O in CdS can result in the formation of nanocrystalline oxygenated CdS, which increases the band gap of the window layer and hence reduces the current loss caused by the absorption of the CdS window layer. [6][7][8][9][10][11] It has also been reported that the presence of O in CdS window layers can help optimize the interdiffusion at CdS/CdTe interface and therefore improve cell performance. 2,12 CdS:O window layers are usually synthesized by the reactive RF sputtering method.…”

“…In the past few years, several groups have reported that the band gap of CdS can be tuned by incorporating oxygen during the sputter deposition. [6][7][8][9][10] Even a small O 2 /(O 2 þ Ar) ratio ($2%) has been reported as sufficient to produce nanocrystalline CdS films with room temperature (RT) sputtering. Therefore, in most reported high efficiency CdTe thin-film solar cells, the CdS:O window layers are deposited at RT by RF sputtering.…”

Application of copper thiocyanate for high open‐circuit voltages of CdTe solar cells

“…The new CdTe cells used CdS:O window layers, sputtered at room temperature (RT) using a 5% oxygen ambient. The oxygenated CdS is supposed to improve the blue response because of the enlarged bandgap . The solar cells were then completed with our standard CdCl 2 activation and CuSCN/Au or Cu/Au back contacts.…”