Multiple Effects of the CdCl2 Activation Treatment on the Device Properties of CdTe/CdS Solar Cells by Monitoring the Annealing Temperature

In our laboratory we fabricate high efficiency CdTe solar cells, exceeding 15 % efficiency, with a lowtemperature process, where all the layers are deposited by vacuum evaporation with temperature below 450 °C. TheCdCl2 treatment is typically prepared by putting drops of a methanol solution with a specific concentration of CdCl2.Starting from a previous work where we studied the effect of the different amount of CdCl2 by changing the methanolconcentration, we have this time analyzed the recrystallization treatment by changing the annealing temperature from310 °C up to 410 °C in air. By doing so we address the multiple effects that this process has on the material anddevice properties for CdTe solar cells.Activated CdTe layers have been analyzed by means of X-Ray diffraction spectroscopy and atomic force microscopy.Finished devices with efficiencies from 8% for the low temperature annealing up to more than 14% for the hightemperature ones, have been analyzed by current-voltage, capacitance-voltage and drive level capacitance profilingtechniques, showing that net carrier concentration is dependent with temperature. A detailed analysis of the formationof intermixed CdS/CdTe layer with temperature is also reported by external quantum efficiency.