Raman scattering peak position of Cu(In, Ga)Se2 film to predict its near-surface [Ga] / ([Ga] plus [In]) and open-circuit voltage

Cu(In, Ga)Se-2 (CIGS) solar cells were fabricated on both rigid soda-lime glass (SLG) and flexible stainless steel (SUS) substrates. Their absorbers, with several [Ga] /([Ga] + [In]) profiles, were deposited using the so-called "multi-layer precursor method", consisting of Ga-Se/In-Se/Cu-Se stacked precursors. It was revealed that the open-circuit voltage (V-OC) of the CIGS solar cell is well correlated with the near-surface GGI, defined as the average [Ga] /([Ga] + [In]) ratio within 200 nm of the CIGS surface. The near-surface GGI could be predicted when the Raman scattering peak position of the CIGS film was known. The estimated penetration depth of Raman scattering light into the CIGS layer was approximately 100-140 nm from its surface. Moreover, a relationship between VOC and the Raman scattering peak position was observed. Ultimately, the Raman scattering peak position, corresponding to the near-surface GGI of below 0.45, could be utilized as an indicator of VOC of CIGS solar cells on both rigid SLG and flexible SUS substrates without cell fabrication, which is measured by the rapid and non-destructive method. (C) 2014 Elsevier B.V. All rights reserved.