Composition dependence of the Raman A₁ mode and additional mode in tetragonal Cu–In–Se thin films

Abstract

Composition dependence of Cu-In-Se films with nominal 60 nm thickness grown on Na-free glass substrates has been systematically investigated by Raman scattering and x-ray diffraction spectra. The most intense A 1 mode shift from 175 cm −1 for Cu 1.5 InSe 2 to 151 cm −1 for CuIn 5 Se 8 indicates weakening of the bond-stretching forces with decrease in Cu content. According to the evolution of the phonon frequencies in films, we found that the Raman bands around 160 and 174 cm −1 observed in CuIn 5 Se 8 are probably due to the other ordered structure phase which is very similar to chalcopyrite-related CuIn 5 Se 8 . Such coexistence mechanism of both structure phases should be associated with the influence of preferred (112) orientation in the films. Comparing our experimental data with the reported data of the related compounds, we explain the composition effect on phonon frequencies shift from Cu-rich to Cu-poor transition in this paper.

Raman scattering characterisation of electrochemical growth of CuInSe2 nanocrystalline thin films for photovoltaic applications: Surface and in‐depth analysis

“…In addition, the presence in the measured spectra of a contribution at the low frequency side of the main CuInSe 2 vibrational mode is attributed to the presence of ordered vacancy compound (OVC) domains. As reported in the literature, [3] this secondary phase is formed as a result of local copper deficiency conditions during crystal growth, and is characterised by a crystallographic structure that includes an ordered array of point defects in the primary chalcopyrite structure.…”

“…This has been attributed to the presence of Cu-deficient domains with chalcopyrite related crystallographic order, reported in the literature as OVCs. [3,7] These compounds show a red shift of the main A 1 vibrational mode with respect to its position in [3] which suggests the presence of a lower average amount of vacancies in the structure. This contrasts with the overall Cu-rich composition of the layers, and points out the higher complexity of the ED grown layers in relation to those fabricated using vacuum-based deposition processes.…”

“…The main peak appears at about 177 cm −1 , and has been identified with the A 1 vibrational mode from CuInSe 2 . This constitutes the main vibrational mode from chalcopyrite ordered CuInSe 2 , which shows four additional modes (B (2) 1 ⊕ B (2) 2 ⊕ 2E (3,4) ) in the spectral region between 173 and 216 cm −1 . [4] Overlapping of these modes leads to a wide spectral contribution in the experimental spectra, and it is not possible in this case to resolve these lower intensity bands.…”

Raman microprobe characterization of electrodeposited S-rich CuIn(S,Se)2 for photovoltaic applications: Microstructural analysis

“…Their Raman spectrum is characterized by a strong redshift of the A 1 mode with respect to the vacancy-free chalcopyrite crystal, which is caused by the missing bonds in the OVC structure. The energy of the A 1 mode depends on the final stoichiometry of the OVC, 11 being 154 cm −1 for CuIn 3 Se 5 . 12 On the other hand, it is evident that the film stoichiometry of the investigated precursors requires a mechanism to accommodate the Cu and Se excess in the film.…”

Chemical bath deposition route for the synthesis of ultra-thin CuIn(S,Se) 2 based solar cells

“…Additionally, the intensity of the 228 cm −1 mode increases (see spectrum b3) under 785 nm excitation. Under this condition, the increase of this contribution is assigned to the presence of Ordered Vacancy Compound (OVC) phases, as is illustrated in the OVC reference spectra (corresponding to CuIn 3 Se 5 ) in the same figure [24]. Differences between the reference and the absorber spectra correspond to different OVC compositions (OVC phases have several stoichiometries including CuIn 5 Se 8 , CuIn 2 Se 3.5 , and CuIn 1.5 Se 2 ) [24,25].…”