Photoluminescence spectroscopy and decay time measurements of polycrystalline thin film CdTe/CdS solar cells

The results of room temperature photoluminescence spectroscopy and decay ti me measurements carried out on CdTe/CdS solar cells are reported. The as-gr own structures were annealed in air at temperatures in the range 350-550 de greesC. For excitation via the CdTe/CdS interface, longer photoluminescence decay times were observed as the anneal temperature was increased, this is attributed to localized passivation of nonradiative states possibly due to the effect of S interdiffusion. When the photoluminescence is excited via the CdTe free surface, the decay curves consist of a fast and slow componen t. The fast component (<130 ps) of the photoluminescence is attributed to n onradiative recombination at grain boundaries or the CdTe free surface. The slow component is attributed to the effects of carrier drift and diffusion and subsequent recombination at the CdTe/CdS interface. Modeling of the tr ansport process has led to the extraction of a value of 0.20 +/- 0.03 cm(2) s(-1) for the minority carrier diffusion coefficient of the CdTe for the s ample annealed at 450<degrees>C. These results are correlated with improvem ents in device efficiency determined from illuminated current density-volta ge measurements. (C) 2000 American Institute of Physics. [S0021-8979(00)070 24-9].