Dielectric functions and optical constants modeling for CuIn 3Se5 and CuIn5Se8

The complex dielectric functions, ε (ω) = ε1 (ω) +i ε2 (ω), of CuIn3Se5 and CuIn5Se8 crystals with different Cu contents have been determined in the 0.8-4.7 eV photon energy range by using spectroscopic ellipsometry. The spectral dependence of the real, ε1 (ω), and imaginary, ε2 (ω), parts of ε (ω), as well as the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity, has been modeled by using a modification of Adachi's model. The results are in excellent agreement with the experimental data over the entire range of photon energies. The model parameters, including the energies corresponding to the lowest direct gap, E0, and to higher critical points, have been determined by using the simulated annealing algorithm. © 2008 American Institute of Physics.Peer Reviewe

Light Induced Increase of Electron Diffusion Length in a p n Junction Type CH3NH3PbBr3 Perovskite Solar Cell

High band gap, high open circuit voltage solar cells with methylammonium lead tribromide MAPbBr3 perovskite absorbers are of interest for spectral splitting and photoelectrochemical applications, because of their good performance and ease of processing. The physical origin of high performance in these and similar perovskite based devices remains only partially understood. Using cross sectional electron beaminduced current EBIC measurements, we find an increase in carrier diffusion length in MAPbBr3 Cl based solar cells upon low intensity a few percent of 1 sun intensity blue laser illumination. Comparing dark and illuminated conditions, the minority carrier electron diffusion length increases about 3.5 times from Ln 100 50 nm to 360 22 nm. The EBIC cross section profile indicates a p amp; 8722;n structure between the n FTO TiO2 and p perovskite, rather than the p amp; 8722;i amp; 8722;n structure, reported for the iodide derivative. On the basis of the variation in space charge region width with varying bias, measured by EBIC and capacitance amp; 8722;voltage measurements, we estimate the net doping concentration in MAPbBr3 Cl to be 3 amp; 8722;6 1017 cm amp; 8722;

Preparation and optical characterization of Cu2ZnGeSe4 thin films

Cu2ZnGeSe4 (CZGSe) films have been fabricated by ion beam sputtering onto glass substrates at a substrate temperature of 300 and 420 K. CZGSe films were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, scanning electron microscopy and by the method of normal incidence transmittance and reflectance. XRD studies reveal an improved crystallinity of the polycrystalline CZGSe films with tetragonal structure when the substrate temperature was increased. The refraction index and extinction coefficient were extracted from the optical measurements. Spectral dependence of the absorption coefficient and the energy band gaps values of CZGSe films were also determinedFinancial supports from IRSES PVICOKEST 269167, MICINN projects (KEST-PV; ENE2010- 21541-C03-01/-02/-03) and FRCFB 13.820.05.11/BF projects are acknowledged. RC also acknowledges financial support from Spanish MINECO within the program Ramón y Cajal (RYC-2011-08521

Time resolved investigation of Cu In,Ga Se2 growth and Ga gradient formation during fast selenization of metallic precursors

Ga segregation at the backside of Cu In,Ga Se2 solar cell absorbers is a commonly observed phenomenon for a large variety of sequential fabrication processes. Here, we investigate the correlation between Se incorporation, phase formation and Ga segregation during fast selenisation of Cu In Ga precursor films in elemental selenium vapour. Se incorporation and phase formation are analysed by real time synchrotron based X ray diffraction and fluorescence analysis. Correlations between phase formation and depth distributions are gained by interrupting the process at several points and by subsequent ex situ cross sectional electron microscopy and Raman spectroscopy. The presented results reveal that the main share of Se incorporation takes place within a few seconds during formation of In Se at the top part of the film, accompanied by outdiffusion of In out of a ternary Cu In Ga phase. Surprisingly, CuInSe2 starts to form at the surface on top of the In Se layer, leading to an intermediate double graded Cu depth distribution. The remaining Ga rich metal phase at the back is finally selenised by indiffusion of Se. On the basis of a proposed growth model, we discuss possible strategies and limitations for the avoidance of Ga segregation during fast selenisation of metallic precursors. Solar cells made from samples selenised with a total annealing time of 6.5 amp; 8201;min reached conversion efficiencies of up to 14.2 total area, without anti reflective coating . The evolution of the Cu In,Ga Se2 diffraction signals reveals that the minimum process time for high quality Cu In,Ga Se2 absorbers is limited by cation ordering rather than Se incorporatio

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 devicesThe research leading to the presented results was partially supported by the European Project INFINITE-CELL (Ref. H2020-MSCA-RISE-2017-777968, 2017–2021, www.infinitecell.eu) and the Spanish MINECO Projects “WINCOST” (ENE2016-80788-C5-2-R) and PHOTOMANA (TEC2015- 69916-C2-1-R). The authors from the Institute of Applied Physics appreciate the financial support from STCU 6224 and from the Institutional Project No. CSSDT 15.817.02.04

Metal acetate based synthesis of small sized Cu2ZnSnS4 nanocrystals effect of injection temperature and synthesis time

We report the colloidal synthesis of small sized Cu2ZnSnS4 CZTS nanocrystals NCs via a hot injection method using zinc and tin acetates in combination with copper acetylacetonate as metal precursors. A systematic investigation of the in amp; 64258;uence of the injection temperature in the range from 190 o C to 300 o C on the size distribution, composition and phase purity of CZTS nanocrystals has been performed. It has been found that temperature plays the key role in changing of the metal sources reactivity and in amp; 64258;uences the amp; 64257;nal composition of the nanocrystals. The mechanism of nanocrystal formation has been investigated by Raman spectroscopy of aliquots of their solutions. It starts from the formation of a Cu2 xS phase as a core followed by the incorporation of Zn2 and Sn4 atoms into its structure regardless of injection temperature

Effect of Ag incorporation on structure and optoelectronic properties of Ag1 xCux 2 ZnSnSe4 solid solutions

The performance of Cu2ZnSnSe4 solar cells is presently limited by low values of open circuit voltage which are a consequence of strong band tailing and high level of nonradiative recombination. Recently, the partial substitution of Cu, Zn, and Sn by other elements has shown the potential to overcome this limitation. We explored the structural changes and the effect on the optoelectronic properties of the partial substitution of Cu with Ag in Cu2ZnSnSe4. This paper clari amp; 64257;es the crystal structure of Ag1 amp; 8722;xCux 2ZnSnSe4 solid solution series, deducing possible cationic point defects and paying special attention to the presence of Cu Zn disorder with a combination of neutron and x ray diffraction. The optoelectronic properties of the solid solution series are assessed using re amp; 64258;ection and quantitative photoluminescence spectroscopy, which allows us to estimate the fraction of nonradiative recombination, which would contribute to the open circuit voltage loss in devices. The results strongly suggest Ag incorporation as a promising route to eliminate Cu Zn disorder and to reduce nonradiative recombination losses in Cu2ZnSnSe4

Mechanochemical synthesis of the lead free double perovskite Cs2[AgIn]Br6 and its optical properties

Hitting hard on the binary halides yields in the formation of Cs2[AgIn]Br6. The lead free double perovskite marks, although not usable itself, a further step forward in finding sustainable and durable perovskite materials for photovoltaic applications. Cs2[AgIn]Br6 is one of the prominent examples of double perovskites materials that have been suggested to circumvent the use of lead compounds in perovskite solar cells. We herein report the successful synthesis of the material using a mechanochemical approach. It crystallizes in an elpasolite type structure, an ordered perovskite superstructure, with a cell parameter of a 11.00 . However, the compound exhibits a relatively large optical bandgap of 2.36 eV and is unstable under illumination, which impedes its use as solar absorber material at this early stage. Still, substitution of lead and the potential of this synthesis method are promising as well as the fruitful combination of theoretical considerations with experimental materials discover

Optical properties of Cu2ZnGeSe4

Sursa: Conferința –"Materials Science and Condensed Matter Physics", Chișinău, Moldova, 11-14 septembrie 2012.→ https://ibn.idsi.md/collection_view/483Cu2ZnGeSe4 (CZGSe) is interesting and promising p-type semiconductor materials for optoelectronics applications and solar cells. In this paper we present reflectivity spectra measured at 300 K in the photon energy range of 1.5 - 6 eV. CZGSe crystals were grown by one-temperature method