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 Depositi on (CBD) was used to deposit the CdS window layers. The annealing process i nduces the formation of a chloride-rich surface layer on CdS as evidenced f rom X-ray photoelectron spectroscopy measurements. The carbon impurity in h eterostructures appears to influence the chloride-promoted recrystallisatio n 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 mater ial 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 hi gh concentrations of impurities in our cells suggests that wet chemical met hods may have great potential in the fabrication of large area/low cost dev ices.