Temperature and power dependent photoluminescence (PL) measurements were employed in order to study defects in close-space-sublimation grown polycrystalline cadmium telluride layers that had been activated with different chlorine containing compounds. The samples were either measured as-grown or after thermal treatment in an oxygen containing ambient with and without the chlorine containing compounds such as cadmium chloride, hydrochloric acid, and sodium chloride. The as-grown sample is discussed in detail, in order to then demonstrate the changes in the PL spectra induced by the postdeposition treatments. A deep level transition at 1.32 eV was observed in the as-grown sample which can be correlated with cadmium vacancies. Due to postdeposition treatments this deep level transition disappears and a broad band correlated with A-centers arises instead at about 1.43 eV. Another transition band at 1.479 eV in the as-grown sample is not influenced by any postdeposition treatment. Furthermore, by processing solar cells out of the respective samples, the PL results can be related to the solar cell parameters.

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The formation of ternary CdSxTe1–x alloys during CdTe solar cell production is quantitatively investigated using optical and quantum efficiency measurements. Both the diffusion of sulphur into the CdTe and of tellurium into the CdS film are analysed in the context of film thicknesses and the activation step used in CdTe solar cell processing. We present a method of determining the tellurium content in the CdS layer from EQE measurements. The tellurium content is limited to small values and depends on the CdS thickness. A CdSxTe1–x phase of several 100 nm thickness is generated in the CdTe film during the activation step. This phase changes the optical bandgap in the depletion region and gains importance in cells with thin absorbers. The comparison of solar cells with and without CdS layer illustrates the crucial role of the CdS buffer layer for the p‐n junction. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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