Influence of Ge addition on the optical properties of As40Se50Ge10 thin film probed by spectroscopy techniques

The thin films of As40Se60 and As40Se50Ge10 were prepared on glass substrates by thermal evaporation method with thickness 1000 nm. The prepared films were amorphous in nature which was confirmed through X-ray diffraction. The chemical composition and the surface picture were obtained from energy dispersive X-ray analysis and Scanning Electron Microscopy analysis. The transmission data of the two films were collected in the wavelength range 400-1000 nm. The transmission percentage is found to be decreased whereas the absorption coefficient is increased with the Ge addition. The addition of Ge into As40Se60 is found to increase the refractive index and the extinction coefficient of As40Se50Ge10 thin film. The decrease in optical band gap is explained on the basis of increase in density of states and disorderness due to Ge addition. The optical absorption in the film is due to allowed indirect transition, and the homopolar bond density is increased with Ge addition. The Raman shift observed in the two films clearly supports the optical changes due to Ge addition

Characterization of thermally evaporated CZTSe thin films used by compositionally controlled alloys

Stoichiometric adjusted Cu2Zn1.5Sn1.2Se4+x (CZTSe) alloys were successfully prepared by a thermal molten method. The pure phase was formed at x = 0.8 as confirmed by XRD and Raman spectroscopy. The bulk alloy was used for thin film coating by thermal evaporation method. The prepared films were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and FT-IR spectroscopy. The XRD and Raman spectroscopy analysis revealed the formation of polycrystalline CZTSe thin films with tetragonal crystal structure after annealing of 450 degrees C. Diode characteristics were studied on the Mo/CZTSe/CdS sandwich geometry. The oxidation state of the selenized film was studied by XPS. The optical band gap of the CZTSe film was about 1.42 eV, which was varying with annealing and selenization condition. The carrier concentration, resistance and mobility of the selenized films were found to be 5.2 x 10(15) cm(-3), 2.2 K Omega/square and 5.5 cm(2)V(-1)s(-1) respectively and the conduction type was p-type. This study sheds light on the effect of annealing and selenization on various phases modifications and the light-harvesting capability of CZTSe solar cells. (C) 2016 Elsevier B.V. All rights reserved

The effect of sulfur on the phase formation of Cu2ZnSnS4 solar cell material

Non-stoichiometry compositions of Cu2Zn1.5Sn1.2S4+x (CZTS) bulk alloys were prepared by the thermal molten technique and characterized by X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM), Electron probe micro analysis (EPMA) and UV-vis absorbance spectroscopy. The results indicate that the secondary phases such as Cu2S, ZnS and SnS etc., are present as identified by XRD and Raman spectroscopy in the lower sulfur content alloys. However, the pure CZTS kesterite phase was obtained in sulfur excess (ie, x=0.4) composition. The backscattered electron images confirm that the transition from a multiphase formation in the alloy to a single phase formation. A direct band gap of about 1.22 eV has been estimated from UV-vis absorbance spectra studies, and this is close to the optimum value of best solar cell efficiency. (C) 2016 Published by Elsevier B.V

Sulfurization and annealing effects on thermally evaporated CZTS films

Thermally evaporated Cu2Zn1.5Sn1.2S4.4 (CZTS) films are annealed and sulfurized at different temperatures to study the structural modifications. The kesterite phase formation and phase purity of the CZTS films are compared and confirmed by X-ray diffraction and Raman spectroscopic technique. Surface oxidation state of the elements in the sulfurized film is studied by XPS. The calculated optical band gap of the 550 degrees C sulfurized CZTS film is found to be 1.56 eV; however getting modified due to annealing and sulfurization. The carrier concentration, resistance and mobility of the sulfurized films are found to be 2.8x10(14) cm(-3), 2686 Omega/square and 8.2 cm(2)V(-1)s(-1) respectively and the conduction type is p-type. This study sheds light on the effect of annealing and sulfurization on various phase-modifications and the light-harvesting capability of CZTS absorber layers for solar cell applications

Morphology Controlled n-Type TiO2 and Stoichiometry Adjusted p-Type Cu2ZnSnS4 Thin Films for Photovoltaic Applications

This paper presents the fabrication and characterization of stoichiometry adjusted Cu2Zn1.5Sn1.2S4.4 thin film (FTO/TiO2/CdS/CZTS/Au) photovoltaic (PV) devices. The PV devices were developed using the window layer of rutile TiO2 nanoarchitecture arrays, i.e., one-dimensional (1D) nanorods and three-dimensional (3D) combined/hierarchical structures (nanorods with microspheres). One-dimensional (1D) nanorods and 3D combined structures of TiO2 window layers were synthesized by a hydrothermal method with different solvents without any assistance of surfactants and templates. We achieved two kinds of TiO2 nanostructures by tuning the precursor concentrations and volume by keeping a constant growth time and temperature. The detailed structural properties were studied using X-ray diffraction and high resolution transmission electron microscopy. Phase formation and chemical state of the prepared samples were examined by Raman spectroscopy and X-ray photoelectron spectroscopy. The surface morphology and luminescence studies of TiO2 nanostructures were analyzed using field emission scanning electron microscopy and cathodoluminescence techniques. The current voltage performance of fabricated devices were measured under an AM 1.5 solar simulator. It is observed that combined structure PV device shows better efficiency (1.45%) than the nanorods alone structure (0.55%). Present work is a first attempt made to construct the inverted CZTS based solar cells. This study establishes the window layer of hierarchical TiO2 nanostructures based morphology that offers a great potential for the development of high-efficiency nonstoichiometric CZTS based solar cells