EFFECT OF CdCl_2 TREATMENT CONDITIONS ON THE DEEP LEVEL DENSITY, CARRIER LIFETIME AND CONVERSION EFFICIENCY OF CdTe THIN FILM SOLAR CELLS

摘要

The effect of CdCl_2 annealing conditions of glass/TCO-CdS/p-CdTe solar cell structures on the deep level density and carrier lifetime of the p-CdTe layer and correlation with the solar cell conversion efficiency was investigated. CdCl_2 treatment was carried out at temperatures ranging from 370 to 460℃ for 15 min. A clear correlation between trap density, carrier lifetime, conversion efficiency and the CdCl_2 annealing conditions was observed. Un-annealed structures had a conversion efficiency of 5.7%, hole trap energy of E_V+0.42eV, hole trap density of 8.71x10~(14)cm~(-3), and decay lifetime of 0.15μs. The optimum CdCl_2 annealing temperature was found to be 415℃ for structures grown at a substrate temperature of 595℃, where the conversion efficiency, hole trap energy, hole trap density, decay lifetime were 13.4%, E_V+0.44eV, 8.10x10~(12) cm~(-3) and 0.40μs, respectively.