Secondary crystalline phases identification in Cu2ZnSnSe4 thin films: contributions from Raman scattering and photoluminescence

In this work, we present the Raman peak positions of the quaternary pure selenide compound Cu2ZnSnSe4 (CZTSe) and related secondary phases that were grown and studied under the same conditions. A vast discussion about the position of the X-ray diffraction (XRD) reflections of these compounds is presented. It is known that by using XRD only, CZTSe can be identified but nothing can be said about the presence of some secondary phases. Thin films of CZTSe, Cu2SnSe3, ZnSe, SnSe, SnSe2, MoSe2 and a-Se were grown, which allowed their investigation by Raman spectroscopy (RS). Here we present all the Raman spectra of these phases and discuss the similarities with the spectra of CZTSe. The effective analysis depth for the common back-scattering geometry commonly used in RS measurements, as well as the laser penetration depth for photoluminescence (PL) were estimated for different wavelength values. The observed asymmetric PL band on a CZTSe film is compatible with the presence of CZTSe single-phase and is discussed in the scope of the fluctuating potentials’ model. The estimated bandgap energy is close to the values obtained from absorption measurements. In general, the phase identification of CZTSe benefits from the contributions of RS and PL along with the XRD discussion.info:eu-repo/semantics/publishedVersio

Optically Induced Structural Transformation in Disordered Kesterite Cu2ZnSnS4

The kesterite structured semiconductor Cu2ZnSnS4is one of the most promising compound for earth abundant low cost solar cells. One of the complex problem on this way deals with its stoichiometry. In this work Raman spectra of Cu rich Cu2ZnSnS4 crystals are discussed in connection with the non stoichiometric composition and disordering within the cat ion sublattice of the kesterite. The shift of the main A peak from 338 to 331 cm 1 and its broadening are attributed here to transition from the kesterite I 4symmetry to the disordered kesterite structure I 2m symmetry . It is shown that this transition may also be driven by an intense light, which could stimulate transformation of Cu ion to Cu2 ions and facilitates generation of CuZn defects on 2d crystalographic position

Polarized Raman scattering analysis of Cu2ZnSnSe4 and Cu2ZnGeSe4 single crystals

The polarized Raman spectra of the Cu2ZnSnSe4 and Cu2ZnGeSe4 single crystals were measured for various in plane rotation angles on the basal 1 1 2 crystal facet. The position of up to 15 for Cu2ZnSnSe4 and 16 for Cu2ZnGeSe4 Raman peaks was determined in the spectral region 50 300 cm 1. From the analysis of the experimental dependence of the inten sity of the Raman peaks with the rotation angle, a symmetry assignment for most of the de tected modes and an estimation of numerical values of Raman tensor elements were derived. The kesterite type structure of Cu2ZnSnSe4 and Cu2ZnGeSe4 single crystals was established by the quantity of the observed nonpolar A and polar B TO LO symmetry mode

Wide band-gap tuning Cu2ZnSn1-xGexS4 single crystals: Optical and vibrational properties

7 págs.; 7 figs.; 3 tabs.The linear optical properties of Cu2ZnSn1¿xGexS4 high quality single crystals with a wide range of Ge contents (x=0.1, 0.3, 0.5, 0.7, 0.9 and 1) have been investigated in the ultraviolet and near infrared range using spectroscopic ellipsometry measurements. From the analysis of the complex dielectric function spectra it has been found that the bandgap E0 increases continuously from 1.49 eV to 2.25 eV with the Ge content. Furthermore, the evolution of the interband transitions E1A and E1B has been also determined. Raman scattering using three different excitation wavelengths and its analysis have been performed to confirm the absence of secondary phases in the samples, and to distinguish between stannite, wurtzite, wurzstannite and kesterite structures. Additionally, the analysis of the high resolution Raman spectra obtained in samples with different [Ge]/([Ge]+[Sn]) ratios allows describing a bimodal behavior of the dominant A modes. The understanding of the incorporation of Ge into the Cu2ZnSnS4 lattice is fundamental in order to develop efficient bandgap engineering of these compounds towards the fabrication of kesterite based solar cells with enhanced performance. & 2015 Elsevier B.V.This work was supported by the Marie Curie-ITN project (KESTCELL, GA: 316488), Marie Curie-IRSES project (PVICOKEST, GA: 269167), AMALIE (TEC2012-38901-C02-01) and SUNBEAM (ENE2013-49136-C4-3-R) project funded by the Spanish Ministry of Economy and Competitiveness. RC acknowledges financial support from Spanish MINECO within the Ramón y Cajal Program (RYC-2011-08521).Peer Reviewe

Multiwavelength excitation Raman scattering of Cu2ZnSn SxSe1 x 4 0 lt; x lt; 1 polycrystalline thin films Vibrational properties of sulfoselenide solid solutions

In this work, Raman spectroscopy and X ray diffraction were applied together to evaluate the crystal structure and the phonon modes of photovoltaic grade Cu 2ZnSn SxSe1 amp; 8722;x 4 thin films, leading to a complete characterization of their structural and vibrational properties. Vibrational characterization has been based on Raman scattering measurements performed with different excitation wavelengths and polarization configurations. Analysis of the experimental spectra has permitted identification of 19 peaks, which positions are in good accord with theoretical predictions. Besides, the observation of Cu 2ZnSnS4 like A symmetry peaks related to S vibrations and Cu 2ZnSnSe4 like A symmetry peaks related to Se vibrations, additional Raman peaks, characteristic of the solid solution and previously not reported, are observed, and are attributed to vibrations involving both S and Se anion

Characterization of secondary phases in Cu poor CuInSe2 Surface and in depth resolved Raman scattering analysis of polycrystalline layers

This work reports the surface and in depth resolved Raman scattering analysis of polycrystalline CuInSe2 layers grown with different chemical composition, as function of the Cu to In content ratio 0.48 amp; 8804; x amp; 8804; 1.14 . Measurements performed at the surface of the Cu poor layers corroborate the formation of both Cu poor Ordered Vacancy Compound OVC and CuAu ordered CuInSe2 phases for compositions corresponding to x amp; 8804; 0.82 OCV and x amp; 8804; 0.66 CuAu , respectively. In depth resolved measurements performed on the layers with lower Cu content have allowed observing a strong decrease with the depth of the intensity of the Raman peak from the chalcopyrite ordered CuInSe2 phase. This suggests a preferential formation of both OVC and CuAu ordered phases at the region close to the interface with the back Mo layer. On the other hand, the comparison between the spectra directly measured on the front and back surfaces of the layers after removal of the layers from the Mo coated glass substrates suggests also a worsening of the crystalline quality at the back region of the layers in the whole range of compositions

Discrimination and detection limits of secondary phases in Cu2ZnSnS4 using X ray diffraction and Raman spectroscopy

The formation of single phase Cu2ZnSnS4 thin films is known to be challenging, mainly due to the difficulties to detect secondary phases in the Cu2ZnSnS4 system. Here, the ability to quantitatively discriminate the most likely secondary phases ZnS and Cu2SnS3 from Cu2ZnSnS4 using common approaches but also using more complex and time consuming Rietveld refinement analysis techniques to analyse X ray diffractograms is investigated in a comparative study to the peak analysis of Raman spectra measured with standard conditions. In studying not only individual samples of the respective phases but also a phase gradient sample containing various amounts of Cu2SnS3 and ZnS alongside Cu2ZnSnS4, we found that refinement analyses can only discriminate more than 10 ZnS and 50 Cu2SnS3 from Cu2ZnSnS4, respectively. In comparison, Raman measurements performed with green wavelength excitation can discern more than 30 Cu2SnS3 from Cu2ZnSnS4 while ZnS is indiscernible. The results show that the identification of secondary phases in the Cu2ZnSnS4 system is more difficult than currently assumed in literature. Furthermore, the potential of multiple wavelength Raman spectroscopy as a tool to identify ZnS secondary phases is shown. Characterization of a Sn rich sample composition nearly Cu2ZnSn3S8 shows no sign of a Sn rich quaternary phase, questioning its existence under typical annealing condition