It is known, that the interface CdS/CdTe plays an important role in the solar cells. A deeper understanding should be achieved, in order to improve the photovoltaic conversion efficiency.
In this work, we have used low temperature photoluminescence (PL) technique to study thin film polycrystalline CdS/CdTe solar cells. The CdS and CdTe films were grown by chemical bath deposition (CBD) and closed space vapor transport (CSVT) techniques, respectively. The samples were subject to post-growth treatment, consisted of evaporating a CdCl2 layer and heating in air, in order to improve device efficiency.
We have compared PL spectra of two cells with 8 and 11.7 % efficiencies. Three bands were identified around 1.41, 1.54 and 1.78 eV. The low energy band has been identified as impurity band associated with the CdTe layer. Two others peaks correspond to intermixing regions between CdTe and CdS layers. The 11.7% efficiency sample shows the higher intensity for the 1.78 eV band from the CdS/CdTe interface. This change, in the PL intensity is indicative of a reduction in non-radiative recombination centers in the near interface region. Temperature dependent PL has been used to obtain the activation energies, associated with recombination routes. We discuss correlations between PL data and device efficiency of the cells.
Work supported by CONACYT-MEXICO under PROJECT 50360-Y.
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