CuAlxGa1−xSe2 thin films for photovoltaic applications: Optical and compositional analysis (original) (raw)
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Solar Energy Materials and Solar Cells, 2011
CuGaSe 2 chalcopyrite thin films Chemical vapor transport Structure and phase transition Oxidation Doping Local and electronic band structure a b s t r a c t Device-grade ternary Cu-Ga-Se chalcopyrite thin films used for photovoltaic energy conversion have been prepared by a novel chemical close-spaced vapor transport (CCSVT) technique developed for a deposition on areas of up to 10 Â 10 cm 2 . A two-step process has been developed which allows the fine tuning of the film composition and the electronic properties. The extension of deposition times in the two-step process led to final film compositions with [Ga]/[Cu] ratios ranging from 0.9 to 5.7, allowing the study of the structural phase transitions. In this paper the main focus of interest is related to the material properties of the device-grade thin films prepared by CCSVT technique. We present our recent studies on (i) the growth, compositional, structural and electronic structural properties, (ii) the degradation under ambient conditions and (iii) the feasibility of n-type doping this p-type semiconducting material by germanium. Thin films were grown with chalcopyrite (1:1:2) and CuGaSe 2 -related defect compound structures (DC) with stoichiometries of CuGa 3 Se 5 and CuGa 5 Se 8 . In order to derive the DC structure, X-ray and neutron powder diffraction investigations have been carried out on powders of these CuGaSe 2 -related compounds grown by elemental synthesis (powder) and CCSVT (thin films), respectively. We found no hints for an ordering of defects, as proposed in the past and giving name to the so-called Ordered Defect Compounds (ODC) in this and related structures. From our results a growth model is presented for CuGa 3 Se 5 formation in gallium-rich CCSVT-grown CuGa x Se y films. The chemical and electronic surface and interface structure of CuGaSe 2 thin films with bulk [Ga]/[Cu] ratios between 0.94 and 1.39 is investigated by X-ray and UV-excited photoelectron spectroscopy (XPS and UPS, respectively). A transition of the Cu:Ga:Se surface composition from 1:1:2 for the Cu-rich bulk sample to 1:3:5 for the sample with the highest bulk [Ga]/[Cu] ratio is observed. Simultaneously, a downward shift of the valence band maximum position with respect to the Fermi energy is found. The comparison of the estimated conduction band minimum with that of CdS reveals the formation of a pronounced ''cliff-like'' conduction band offset at the respective interface.
Materials Letters, 2015
Investigation on chalcopyrite structures is crucial for making further progress in thin films technology. In this work we present the results on optical, electrical and surface properties of CuIn 0.7 Ga 0.3 (Se 0.4 Te 0.6) 2 (CIGSeTe) multinary compounds thin films with annealing effect. The developed procedure is a twosteps methodology involving the pre-reaction of high purity elements Cu, In, Ga, Se and Te in a carbon coated quartz ampoule and e-beam evaporation for thin film deposition. The availability of a multicomponent absorber layers such as CuInGaSeTe, including all elements in a defined ratio, offers the opportunity to reduce film formation temperatures and thereby also reduce manufacturing costs. This aspect was a great motivation to evaluate these materials as banausic and new trend solar cell materials.
Effect of sodium addition on Cu-deficient CuIn1-xGaxS2 thin film solar cells
Solar Energy Materials and Solar Cells, 2009
Chalcopyrites are important contenders among solar-cell materials due to direct band gap and very high-absorption coefficients. Copper–indium–gallium disulfide (CIGS2) is a chalcopyrite material with a near-optimum band gap of 1.5 eV for terrestrial as well as space applications. At FSEC PV Materials Laboratory, record efficiency of 11.99% has been achieved on a 2.7 μm CIGS2 thin film prepared by sulfurization. There are reports of influence of sodium on copper–indium–gallium selenide (CIGS) as well as copper–indium disulfide (CIS2) solar cells. However, this is the first of its kind approach to study the effect of sodium on CIGS2 solar cells and resulting in encouraging efficiencies. Copper-deficient CIGS2 thin films were prepared with and without the addition of sodium fluoride (NaF). Effects of addition of NaF on the microstructure and device electrical properties are presented in this work.
Optical Absorption Studies on p–CuGa0.25In0.75.Se2 Thin Films
Physica Status Solidi (a), 1991
Optical Absorption Studies on p-C u G a c , 251no 7 5 S e Z Thin F i l m s By Y. APARNA, P.S. REDDY, B. SRINIVASIJLU NAIDU, and P. JAYARAMA REDDY CuInSe2 and CuGaSe have proved to be stable and efficient absorber materials for thin film heterojunction solar cells /I to 5 /. These ternary chalcopyrite compounds are direct bandgap semiconductors showing a threefold optical structure I6 / near the fundamental edge due to crystal-field and spin-orbit splitting of the uppermost valence band. The quaternary CuGaxInl-xSe2 system /7, 8 / allows tailoring of the optical bandgap for optimum solar energy conversion. By gradually substituting In by Ga the optical bandgap can be increased from 1.04 to 1.68 eV. In this note the optical absorption of CuGao. 251no. 75Se2 films is reported. Stoichiometric CuGaO. 251no. 75Se2 ingots, prepared b y vacuum fusion of the constituent elements (99.999 % p u r e) , were crushed and ground to 200 to 300 mesh powders. CuGa 0m251n0.75Se2 films of 1.0 pm thickness were prepared b y the flash evaporation technique onto Corning 7059 glass substrates at a pressure of 2~1 0-~ Torr. The temperature of the molybdenum source was kept around 1773 K and the evaporation rate was about 1 nm/s. The substrate temperature was kept at 623 K. 2 CuGaO. 251no. 75Se2 thin films formed at 623 K were polycrystalline and exhibited chalcopyrite structure with lattice parameters a = 0.5721 nm and c = 1.1489 nm, as seen from X-ray diffraction patterns. Thermoelectric power and Hall mobility measurements indicated p-type conduction in the films. The resistivity of the films, measured using the van der Pauw technique was in the range 100 to 150 Rcm. The composition of the films was measured by energy dispersive analysis of X-ray (EDAX) with an accuracy of i1 %. The calculated wt% of copper, gallium, indium,
2006
This study prepared Cu(In,Ga)Se 2 (CIGS) thin films on bi-layer Mo coated soda-lime glass, by printing with mixed powders of CIGS quaternary alloy (average partial size of 680 nm) and NaF. A single-stage annealing process was performed to form a CIGS chalcopyrite phase. Experimental results show stoichiometric ratios of Cu/ (In?Ga) = 0.94 and Ga/(In?Ga) = 0.26 in the CIGS film. The resistivity of the sample was 12.69 X cm, with a carrier concentration of 9.34 9 10 16 cm -3 , and mobility of 5.27 cm 2 V -1 s -1 . The CIGS film exhibited p-type conductivity. The incorporation of 1 wt% NaF in the CIGS powder produced a chalcopyrite structure with the best crystalinity. Raman analysis identified a number of phases, including CuInSe 2 and CuIn 3 Se 5 . The CIGS solar cells with AZO/i-ZnO/CdS/CIGS/Mo/soda-lime glass structure were fabricated. The CIGS thin film solar cells conversion efficiency of 1.23 % on 1 9 1.5 cm 2 .
Journal of Luminescence, 2013
The structural and optical properties of Cu-poor CuIn 1−x Ga x Se 2 thin films with different gallium contents grown using the co-evaporated technique were studied. Measurements of X-ray diffraction (XRD), temperature-dependent photoluminescence (PL), and photoreflectance (PR) were performed on the samples. The emission peaks in the PL spectra and PR spectra observed around 1.0-1.2 eV are attributed to donor-acceptor pairs and defect-related luminescence. With increasing gallium content, the linewidths of the luminescence spectra for the samples become wider, which we attribute to greater statistical disordering between indium and gallium. The structural properties of the CuIn 1−x Ga x Se 2 thin films are further characterized by simulation of the XRD spectra with a theoretical model. It is found that the sample with higher gallium content exhibits less uniformity of microstructure size. The X-ray diffraction line profile analysis also shows a stronger internal strain in the sample with the higher gallium content, which is consistent with its broader microstructure size distribution. The conversion efficiency of the CuIn 1−x Ga x Se 2-based solar cells is also obtained and investigated through theoretical analysis. The experimental results coincide with the inferences given by the X-ray diffraction line profile analysis.
Journal of Physics: Conference Series, 2019
The current work reports the synthesis and characterization of a photovoltaic material based on the CuIn1−xGaXSe2(X = 0.3 y 0.5) system, making use of the doctor blade method. For this purpose, homogeneous inks were obtained and worked under previous stoichiometry arrangement. The deposition process of thin films, were made in a heating plate on conventional glass substrates, previously washed and treated for this purpose. Once the layers of Cu, In, and Ga were deposited by chemical bath, a thermal treatment was performed at 550 °C for 30 min in a conditioned oven, in which the selenization process was performed. The obtained films were characterized by X-ray diffraction, Raman spectroscopy, solid-state impedance spectroscopy, UV spectroscopy and scanning electron microscopy techniques. The identification of the main crystalline phase could be corroborated, as well as the conductive and optoelectronic behavior of the solids in accordance with reported in literature. Simultaneously, ...
Electronic properties of chalcopyrite CuAlX 2(X=S,Se,Te) compounds
Solid State Communications, 2008
We present results of the band structure and density of states for the chalcopyrite compounds CuAlX 2 (X = S, Se, Te) using the state-of-the-art full potential linear augmented plane wave (FP-LAPW) method. Our calculations show that these compounds are direct band gap semiconductors. The energy gap decreases when S is replaced by Se and Se replaced by Te in agreement with the experimental data. The values of our calculated energy gaps are closer to the experimental data than the previous calculations. The electronic structure of the upper valence band is dominated by the Cu-d and X-p interactions. The existence of Cu-d states in the upper valence band has significant effect on the optical band gap.
Preparation and characterization of chalcopyrite compound for thin film solar cells
Alexandria Engineering Journal, 2011
CulnS 2 thin films were electrodeposited onto indium tin oxide substrate by the electrodeposition technique. Cyclic voltammetry and chronoamperometry were carried out to determine the optimum pH and the amount of sodium thiosulfate for electroplating CuInS 2 compound. The composition, crystallinity and optical properties of the compounds synthesized were studied by energy dispersive X-ray (EDX), (SEM), X-ray diffraction and UV-Visible spectra. It was found that the increasing pH shifts the electrodepositions voltage toward more negative and lowers the deposition current. Increasing the amount of sodium thiosulfate also decreases the deposition current but it has no effect on the deposition potential. It was concluded that CuInS 2 with atomic stoichiometric ratio was prepared at pH equals 1 and 150 ml of 0.1 M sodium thiosulfate, 5 ml of 0.1 M indium chloride and 5 ml of 0.1 M cupper acetate. The energy gaps were calculated to be 1.6, 1.7 and 1.75 eV for CuInS 2 prepared at 1, 1.5 and 2 of pH, respectively. It was indicated that the amount of the sodium thiosulfate has a slight effect on the energy gap.