Phonon confinement and strain in CuInS2

Abstract

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.

Process monitoring of chalcopyrite photovoltaic technologies by Raman spectroscopy: an application to low cost electrodeposition based processes

“…In the case of CIS and CISe photovoltaic absorbers, it is well established that the increase of the FWHM of the A 1 band correlates with a worsening of the film crystallinity, as inferred from Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) observations. 8,9 Furthermore, the significance of the absorber crystalline quality has been revealed by several studies that have reported good correlations between the FWHM of the A 1 band and the electrical performance of the corresponding solar cells. In particular, Open Circuit Voltage (V OC ) and cell efficiency (Z) have both shown [10][11][12] to be strongly dependent on the FWHM of the A 1 band.…”

Raman Spectroscopy on Thin Films for Solar Cells

“…In general, either point or extended defects can be responsible for such activation of noncenter phonons because of the breakage of the momentum conservation law. These effects determine a characteristic change in the shape of the main peaks in the spectra, with the appearance of a shoulder at the low-or high-frequency side that is due to the contribution of the modes at the vicinity of the center of the Brillouin zone [17][18][19][20]. The location of this contribution in relation to the frequency of the Raman peak is determined by the dispersion curves of the phonons involved in the process in the vicinity of the q ¼ 0 point: in Si, this contribution appears at the low-frequency side of the Raman peak [19], while semiconductors as CuInS 2 and CuInSe 2 show this disorder-induced contribution at the high-frequency side of the main Raman mode [20].…”

Advanced diagnostic and control methods of processes and layers in CIGS solar cells and modules

“…Accordingly, the analysis of the spectral features of the A 1 mode allows for a direct monitoring of the crystalline quality of the material. Modelling the line shape of the peak gives an estimation of the correlation length in the scattering volume, which is related to the characteristic size of nanocrystal domains where translational symmetry holds 35. The presence of these defects also has a direct impact on solar cell characteristics.…”