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

The results of room temperature photoluminescence spectroscopy and decay time measurements carried out on CdTe/CdS solar cells are reported. The as-grown structures were annealed in air at temperatures in the range 350-550 degreesC. 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 component. The fast component (<130 ps) of the photoluminescence is attributed to nonradiative 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 transport 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 sample annealed at 450<degrees>C. These results are correlated with improvements in device efficiency determined from illuminated current density-voltage measurements. (C) 2000 American Institute of Physics. [S0021-8979(00)07024-9].