Spectroscopic ellipsometry study of Cu2ZnSnSe4 bulk crystals

Journal of Applied Physics, 2010

The dielectric functions of Cu 2 ZnGeS 4 bulk crystals grown by the Bridgman method were measured over the energy range 1.4 to 4.7 eV at room temperature using variable angle spectroscopic ellipsometry. The observed structures in the dielectric functions were adjusted using the Adachi's model and attributed to interband transitions E 0 , E 1A , and E 1B at ⌫:͑000͒, N͑A͒ :2 / a͑0.5 0.5 0.5͒, and T͑Z͒ :2 / a͑0 0 0.5͒ points of the first Brillouin zone, respectively. The model parameters ͑threshold energy, strength, and broadening͒ have been determined using the simulated annealing algorithm. The decrease in the first gap, E 0 , has been attributed to a higher Ge-S hybridization. The spectral dependence of the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity were also derived.

Applied Physics Letters, 2011

Thin Solid Films, 2015

Cu 2 ZnSnSe 4 thin films were synthesised by selenisation of magnetron sputtered metal precursors. The band gap determined from the absorption spectra increases from 1.01 eV at 300 K to 1.05 eV at 4.2 K. In lower quality films photoluminescence spectra show a broad, low intensity asymmetric band associated with a recombination of free electrons and holes localised on acceptors in the presence of spatial potential fluctuations. In high quality material the luminescence band becomes intense and narrow resolving two phonon replicas. Its shifts at changing excitation power suggest donor-acceptor pair recombination mechanisms. The proposed model involving two pairs of donors and acceptors is supported by the evolution of the band intensity and spectral position with temperature. Energy levels of the donors and acceptors are estimated using Arrhenius quenching analysis.

Materials Letters, 2017

We have studied influence of Cu 2 ZnSnSe 4 (CZTSe) and secondary phases of Cu 2 S and SnS on optical properties of kesterite-type Cu 2 ZnSnS 4 (CZTS) by using the effective medium theory. We found that CZTSe and Cu 2 S cause band gap reduction and enhance light absorption of CZTS at all photon energies of the sunlight whereas SnS changes optical properties of CZTS only at large photon energies beyond the solar spectrum. Optical spectra of CZTS(Se) has been studied by first principles calculations within hybrid functional that was used as input for the effective medium theory.

Optics express, 2012

A polycrystalline Cu2ZnSnS4 thin film was deposited on fused quartz by co-evaporation. The selected thickness was ~100 nm to avoid artifacts in its optical properties caused by thicker as-grown films. The composition and phase of the film were checked with x-ray fluorescence, Raman shift spectroscopy, scanning transmission electron microscopy, and energy dispersive x-ray spectroscopy. An improved spectroscopic ellipsometry methodology with two-side measurement geometries was applied to extract the complex dielectric function ε = ε1 + iε2 of the Cu2ZnSnS4 thin film between 0.73 and 6.5 eV. Five critical points were observed, at 1.32 (fundamental band gap), 2.92, 3.92, 4.96, and 5.62 eV, respectively. The ε spectra are in reasonable agreement with those from theoretical calculations.

TRENDS IN SCIENCES , 2023

Following the recent classification by the European Commission of some elements as critical raw materials (CRM), there is an increasing interest in the development of CRM-free thin film photovoltaic (PV) technologies, including kesterite materials. Moreover, starting with the performance breakthrough reported by IBM in 2010, the efficiency of kesterite-based solar cells steadily progressed in the following years achieving. Therefore, in recent years, there has been a significant research effort to develop kesterite-based devices. However, despite the large number of theoretical and experimental works, many aspects of the problem have not yet been fully studied. Therefore, the issues considered in the article, especially the behavior of the absorption and photoconductivity spectra of the Cu2ZnSn[S1−xSex]4 system, depending on the S/Se ratio, are extremely important and, at the same time, one of the topical and poorly studied problems. In this work, using quantum-chemical calculations in the framework of density functional theory (DFT), we study the optical properties of semiconductor nanocrystals of kesterite Cu2ZnSnS4 doped with Se. Using the WIEN2k package, the concentration dependences of the optical characteristics of nanocrystals of the Cu2ZnSn[S1−xSex]4 system (x = 0.00, 0.25, 0.50, 0.75 and 1.00) were calculated. It is shown that doping with Se at the S position leads to a noticeable improvement in the photoabsorbing properties of these nanocrystals, as well as their photoconductivity in the IR range. The calculated absorption and extinction spectra, as well as the refractive indices and permittivity of the materials under study, are compared with experimental data known from the literature. The data obtained will significantly enrich the existing knowledge about the materials under study and will contribute to the expansion of the field of application of these compounds in optoelectronic devices.

2014

In this work, we present the Raman peak positions of the quaternary pure selenide compound Cu 2 ZnSnSe 4 (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, Cu 2 SnSe 3 , ZnSe, SnSe, SnSe 2 , MoSe 2 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.

Letters in Applied NanoBioScience, 2023

In this work, we have studied the geometric structure and electronic and optical properties of Cu2ZnSn(S1-xSex)4 nanocrystals where x = 0, 0.25, 0.50, 0.75, 1.00 by the quantum-chemical calculations within the framework of DFT. For the electronic and optical properties calculations, the effective XC functional and the TB-mBJ potential were used. The calculated structural characteristics show that the volume of these systems increases with increasing the Se concentration. The electronic properties of the Se-doped kesterite Cu2ZnSnS4 show that the bandgap tends to decrease. It was found that the Se-doped material has noticeably increased its absorption capacity. Hence, the efficiency of the Cu2ZnSnS4 in the IR region of radiation improves. The effective reduction bandgap from 1.455 eV to 0.94 eV is observed, which is in gоod agreement with known experimental data for the pure and undoped systems Cu2ZnSnS4 and Cu2ZnSnSе4. The calculated band gap is 1.346 eV for the Cu2ZnSnS3Se system, which is comparable with the optimal bandgap of semiconductors used in photovoltaic applications. It was found that with the increase of the Se concentration, the absorption coefficient increases, thereby resulting in the materials' reflectivity decrease. The calculated optoelectronic parameters and the density of electronic states indicate that the Cu2ZnSnS4:Se system possesses a favorable property, suitable for applications in solar cells technology.

Thin Solid Films, 2011

Cu 2 ZnSnS 4 is a promising semiconductor to be used as absorber in thin film solar cells. In this work, we investigated optical and structural properties of Cu 2 ZnSnS 4 thin films grown by sulphurization of metallic precursors deposited on soda lime glass substrates. The crystalline phases were studied by X-ray diffraction measurements showing the presence of only the Cu 2 ZnSnS 4 phase. The studied films were copper poor and zinc rich as shown by inductively coupled plasma mass spectroscopy. Scanning electron microscopy revealed a good crystallinity and compactness. An absorption coefficient varying between 3 and 4 × 10 4 cm −1 was measured in the energy range between 1.75 and 3.5 eV. The bad gap energy was estimated in 1.51 eV. Photoluminescence spectroscopy showed an asymmetric broad band emission. The dependence of this emission on the excitation power and temperature was investigated and compared to the predictions of the donor-acceptor-type transitions and radiative recombinations in the model of potential fluctuations. Experimental evidence was found to ascribe the observed emission to radiative transitions involving tail states created by potential fluctuations.

Thin Solid Films, 2014

Compositional and structural studies of Cu 2 ZnSnSe 4 (CZTSe) thin films were carried out by X-ray diffraction, energy dispersive X-ray spectroscopy (EDS), particle induced X-ray emission (PIXE), photoluminescence, and Raman spectroscopy. CZTSe thin films with different compositions were deposited on sodalime glass by coevaporation. The composition of the films measured by two different methods, EDS and PIXE, showed significant differences. Generally, the Zn/Sn ratio measured by EDS is larger than that measured by PIXE. Both the micro-PIXE and the micro-Raman imaging results indicated the compositional and structural inhomogeneity of the sample.