In this work annealing and growth of CuInS 2 thin films is investigated with quasireal-time in situ Raman spectroscopy. During the annealing a shift of the Raman A 1 mode towards lower wave numbers with increasing temperature is observed. A linear temperature dependence of the phonon branch of Ϫ2 cm Ϫ1 /100 K is evaluated. The investigation of the growth process ͑sulfurization of metallic precursors͒ with high surface sensitivity reveals the occurrence of phases which are not detected with bulk sensitive methods. This allows a detailed insight in the formation of the CuInS 2 phases. Independent from stoichiometry and doping of the starting precursors the CuAu ordering of CuInS 2 initially forms as the dominating ordering. The transformation of the CuAu ordering into the chalcopyrite one is, in contrast, strongly dependent on the precursor composition and requires high temperatures.

Single crystalline and polycrystalline CuInS2 samples prepared by different methods are characterized by Raman spectroscopy. The measured spectra are fitted according to the phonon confinement model. Correlation lengths were obtained, which correspond to the size of domains of perfect crystallinity. These correlation lengths are in good agreement with distances between twin defects observed by transmission electron microscopy in polycrystalline CuInS2. Additionally, the strain present in the samples was determined from the Raman spectra. A tensile strain was obtained for the polycrystalline CuInS2 thin films, which agrees well with published values for the same material.

In this work spectroscopic features of the Raman A1 mode of CuInS2 thin films are investigated. A broadening of the A1 mode in combination with an asymmetry towards larger wave numbers is observed. The comparison with parameters of the solar cells formed out of these thin films reveal a direct correlation between the linewidth of the A1 mode and the solar cell data. A significant decrease of open circuit voltage and fill factor of the cells is found for linewidths larger than 3.8 cm−1. For linewidths smaller than 3.8 cm−1, a saturated behavior of the solar cell parameters is observed. This saturation indicates other origins of performance limitation to be present in CuInS2 based devices.

No abstract

No abstract