STUDY OF ELECTRO-OPTICAL PROPERTIES OF CdTe SOLAR CELLS PREPARED BY A LOW TEMPERATURE FABRICATION PROCESS

CdTe solar cells are prepared by a low temperature vacuum evaporation, a process suitable for growing flexible cells on polymer substrates, together with an alternative activation post-deposition thermal treatment that avoids the use of dangerous CdCl2. Usual CdCl2 treatment is also employed in order to compare the effect of Freon and CdCl2 annealing procedure on electro-optical properties of the solar cells. The obtained CdTe/CdS/ITO structures are studied as function of Freon annealing temperatures and time. For both treatment procedures the CdTe grain size increase due to the annealing is assessed by SEM analyses. SEM-cathodoluminescence studies show a large increase in the radiative recombination efficiency of the treated CdTe. The luminescence intensities of CL bands, of treated samples, increase of about one order of magnitude, respect to the untreated ones, demonstrating an improvement of the crystalline quality and a decrease of the non-radiative recombination centres in the annealed materials. EBIC analyses showed that no correlation between grain size and signal exists, in addition the comparison with cathodoluminescence mapping evidences that these two contributions are coming from different regions of the sample