Properties of sputtered CdS and CdTe films and performance of CdTe solar cells as a function of annealing temperature

Thin film PV devices were fabricated in FTO/CdS/CdTe/Cu/Au superstrate configuration by RF sputtering of CdS and CdTe films, and CdCl₂ activation process was performed at 370, 380 and 390°C, respectively. Morphological studies indicated for the first time that there were numerous holes randomly distributed at the as-deposited CdS/CdTe interface; although the holes were reduced after CdCl₂ annealing, the p-n junction was greatly improved. Further, the new concept of solar spectrum window width (ΔE_g) for the solar cells was demonstrated, and the ΔE_g of CdTe solar cells was found to be extended with increasing annealing temperature. Moreover, the efficiency of CdTe solar cells was dramatically improved from 0.02% to 12.02% as a function of annealing temperature, and the values of J ₀ and A were reduced with the optimal values (7.2×10^-7 mA/cm² and 1.87), indicating the primary carrier recombination of the best device was Shockley-Real-Hall mechanism in the space charge region.