A study of impurities in some CdS/CdTe photovoltaic cells prepared by wet-chemical methods using secondary ion mass spectrometry and X-ray photoelectron spectroscopy

Quantitative Secondary Ion Mass Spectrometry has been used to determine the elemental profiles and concentrations of isotopes C-12, O-16, S-34 and Cl-35 within n-CdS/p-CdTe thin film photovoltaic cells. Chemical Bath Deposition (CBD) was used to deposit the CdS window layers. The annealing process induces the formation of a chloride-rich surface layer on CdS as evidenced from X-ray photoelectron spectroscopy measurements. The carbon impurity in heterostructures appears to influence the chloride-promoted recrystallisation of CdTe. High concentrations of O-16, of the order 10(20)-10(21) atoms cm(-3) throughout the cells, are consistent with the formation of oxide material in the post-deposition thermal processing. Isotopic profiles for C-12, S-34 and Cl-35 have similar maxima (approximate to 10(19) atoms cm(-3)) but concentrate at the CdS-CdTe interface. The relatively high tolerance to high concentrations of impurities in our cells suggests that wet chemical methods may have great potential in the fabrication of large area/low cost devices.