Influence of laser wavelength on the laser induced breakdown spectroscopy measurement of thin CuIn_(1-x)Ga_xSe2 solar cell films

摘要

Laser induced breakdown spectroscopy (UBS) measurement of thin CuIn_xGa_(1-x)Se2 (CIGS) films (1.2-1.9 urn) with varying Ga to In ratios was carried out using the fundamental (1064 nm) and second harmonic (532 nm) wavelength Nd: YAG lasers (t = 5 ns, spot diameter = 150 urn, top-hat profile) in air. The concentration ratios of Ga to In, X_(Ga) = Ga/(Ga + In), of the CIGS samples ranged from 0,027 to 0,74 for which the band gap varied nearly proportionally to x_(Ga) from 0.96 to 1.42. It was found that the LIBS signal of 1064 nm (1.17 eV) wavelength laser was significantly influenced by x_(Ga), whereas that of the 532 nm (2.34 eV) laser was consistent for all values of x_(Ga). The observed dependency of the LIBS signal intensity on the laser wavelength was attributed to the large difference of photon energy of the two wavelengths that changed the absorption of incident laser energy by the film. The 532 nm wavelength was found to be advantageous for multi-shot analysis that enabled depth profile analysis of the thin CIGS films and for improving measurement precision by averaging the multi-shot UBS spectra.