Impact of Various Cu Contents on Raman Spectra from Cu(In,Ga)Se2 Thin Films

Abstract

This paper reports the Raman scattering analysis of Cu(In,Ga)Se2(CIGS) thin films with Cu/(Ga+In) ratio ranging from 0.748 to 0.982. CIGS thin films were prepared by magnetron sputtering and subsequent selenization process. Frequencies of CIGS Raman peaks do not shift obviously as Cu/(Ga+In) varying around 0.9. Otherwise, the full width at half maximum (FWHM) of the A1 peak reaches its minimum at Cu/(Ga+In) near 0.9 due to better crystallinity and less disorder. Similar phenomena of Raman peaks at 64 cm−1and 72 cm−1were also observed. Since the Cu/(Ga+In) ratio of most high efficiency CIGS solar cells is around 0.9[1,2], the FWHM-Cu/(Ga+In) relationship derived from Raman spectra can be used for non-destructive composition measurement and crystallinity assessment. Furthermore, Cu-poor film shows a broad shoulder at around 150 cm-1 as a result of ordered vacancy compounds (OVC)[3], and Cu-rich film exhibits a peak at around 260 cm-1 corresponding to Cu2Se phase[4].