Polarized Raman scattering study of kesterite type Cu2ZnSnS4 single crystals

A non-destructive Raman spectroscopy has been widely used as a complimentary method to X-ray diffraction characterization of Cu2ZnSnS4 (CZTS) thin films, yet our knowledge of the Raman active fundamental modes in this material is far from complete. Focusing on polarized Raman spectroscopy provides important information about the relationship between Raman modes and CZTS crystal structure. In this framework the zone-center optical phonons of CZTS, which is most usually examined in active layers of the CZTS based solar cells, are studied by polarized resonant and non-resonant Raman spectroscopy in the range from 60 to 500 cm(-1) on an oriented single crystal. The phonon mode symmetry of 20 modes from the 27 possible vibrational modes of the kesterite structure is experimentally determined. From in-plane angular dependences of the phonon modes intensities Raman tensor elements are also derived. Whereas a strong intensity enhancement of the polar E and B symmetry modes is induced under resonance conditions, no mode intensity dependence on the incident and scattered light polarization configurations was found in these conditions. Finally, Lyddane-Sachs-Teller relations are applied to estimate the ratios of the static to high-frequency optic dielectric constants parallel and perpendicular to c-optical axis

Time resolved photoluminescence on Cu(In, Ga)Se-2 absorbers: Distinguishing degradation and trap states

Recent reports have suggested that the long decay times in time resolved photoluminescence (TRPL), often measured in Cu(In, Ga)Se-2 absorbers may be a result of detrapping from sub-bandgap defects. In this work, we show via temperature dependent measurements, that long lifetimes >50 ns can be observed that reflect the true minority carrier lifetime not related to deep trapping. Temperature dependent time resolved photoluminescence and steady state photoluminescence imaging measurements are used to analyze the effect of annealing in air and in a nitrogen atmosphere between 300K and 350K. We show that heating the Cu(In, Ga)Se-2 absorber in air can irreversibly decrease the TRPL decay time, likely due to a deterioration of the absorber surface. Annealing in an oxygen-free environment yields a temperature dependence of the TRPL decay times in accordance with Schockley Read Hall recombination kinetics and weakly varying capture cross sections according to T-0.6. Published by AIP Publishing

Spectroscopic ellipsometry study of Cu2ZnSnSe4 bulk crystals

Using spectroscopic ellipsometry we investigated and analyzed the pseudo-optical constants of Cu2ZnSnSe4 bulk crystals, grown by the Bridgman method, over 0.8-4.5 eV photon energy range. The structures found in the spectra of the complex pseudodielectric functions were associated to E0, E1A, and E1B interband transitions and were analyzed in frame of the Adachi's model. The interband transition parameters such as strength, threshold energy, and broadening were evaluated by using the simulated annealing algorithm. In addition, the pseudo-complex refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity were derived over 0.8-4.5 eV photon energy rang

Spectroscopic ellipsometry study of Cu2ZnSnS4 bulk poly-crystals

The linear optical properties of Cu2ZnSnS4 bulk poly-crystals have been investigated using spectroscopic ellipsometry in the range of 1.2-4.6 eV at room temperature. The characteristic features identified in the optical spectra are explained by using the Adachi analytical model for the interband transitions at the corresponding critical points in the Brillouin zone. The experimental data have been modeled over the entire spectral range taking into account the lowest E0 transition near the fundamental absorption edge and E1A and E1B higher energy interband transitions. In addition, the spectral dependences of the refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity values have been accurately determined and are provided since they are essential data for the design of Cu2ZnSnS4 based optoelectronic devices

Chemistry and Dynamics of Ge in Kesterite : Toward Band-Gap- Graded Absorbers

peer reviewe

Earth abundant thin film solar cells from co-evaporated Cu2SnS3 absorber layers

Cu2SnS3 (CTS) is starting to gain interest in the PV research community as an alternative earth abundant absorber for thin film photovoltaics. In this work, the structure, morphology and the composition of the CTS absorbers as well as their influence on the optoelectronic properties of the solar cells are analysed. The synthesis of Cu-Sn-S thin films by co-evaporation at a nominal temperature of 400 °C is presented. A combination of X-ray diffraction, Raman and UV-Vis spectroscopy suggests that the Cu2SnS3 is crystallising in a cubic structure with disorder in the Cu and Sn sites, leading to substantial band tailing. The best device was fabricated from absorbers exhibiting a Cu/Sn ratio of approximately 1.7 and had an efficiency of 1.8%, a short circuit current of 28 mA cm−2, and an open circuit voltage of 147 mV with a fill factor of 42.9%. From the quantum efficiency measurement, we estimate a band gap of 1.06 eV for the CTS absorber material. Capacitance-voltage measurements show charge carrier concentrations between 4 and 6 × 1016 cm−3

Raman scattering and spectroscopic ellipsometry studies of Sb2S3 and Sb2Se3 bulk polycrystals

6 pags., 5 figs., 2 tabs.Antimony sulfide (Sb2S3) and antimony selenide (Sb2Se3) compounds have attracted considerable attention for applications in different optoelectronic devices due to their notable optical and electrical properties, and due to the strong anisotropy of these properties along different crystallographic directions. However, the efficient use of these promising compounds still requires significant efforts in characterization of their fundamental properties. In the present study, Raman scattering and spectroscopic ellipsometry were used to investigate the vibrational and optical properties of Sb2Se3 and Sb2S3 bulk polycrystals grown by the modified Bridgman method. The first technique proved the presence of the desired Sb2S3 and Sb2Se3 phases in the analyzed ingots and confirmed the absence of any preferential crystallographic orientation at the measured surface of the samples. Spectroscopic ellipsometry was performed using a multi-oscillator Tauc-Lorentz dispersion model, and yielded a complex dielectric function of chalcogenides over the range 1.0-4.6 eV with a three phase model (ambient, surface and bulk materials). Finally, spectral data on the refractive index, the extinction coefficient, the absorption coefficient and the reflectivity at normal incidence, R, were obtained, which serve as a reference for the optical modeling of optoelectronic devices based on polycrystalline Sb2S3 and Sb2Se3 compounds.The authors from Moldova State University, Institute of Applied Physics appreciate the financial support from the Institutional Project ANCD 20.80009.5007.03. This work was also supported by the Spanish Ministry of Science and Innovation (MCIN) and the Agencia Estatal de Investigación (AEI) 10.13039/501100011033 and by the European Union NextGenerationEU/PRTR grants ASSESS (TED2021-129666B-C21), the CELL2WIN (PID2019-104372RB-C32), the MaterOne (PID 2020-116719RB-C42), and the ALPHOMENA (PID2021-123190OB-I00). The authors from IREC belong to the MNT-Solar Consolidated Research Group of the “Generalitat de Catalunya” (ref. 2021 SGR 01286) and are grateful for the support from European Regional Development Funds (ERDF, FEDER Programa Competitivitat de Catalunya 2007–2013). V. R. acknowledges the support from the predoctoral program AGAUR-FI ajuts (2023 FI-1 00436), Joan Oró of the Secretariat of Universities and Research of the Department of Research and Universities of the Generalitat of Catalonia and the European Social Plus Fund. M. G. acknowledges the financial support from the Spanish Ministry of Science, Innovation and Universities within the Juan de la Cierva fellowship (IJC2018-038199-I).Peer reviewe