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Growth and structural characterization of Cu 2 ZnSnSe 4 compound for solar cells 1
Canadian Journal of Physics
Abstract
This work reports results concerning the effect of the deposition parameters on the structural properties of Cu2ZnSnSe4 thin films, grown through a chemical reaction of the metallic precursors via coevaporation in a three-stage process. X-ray diffraction measurements revealed that the samples deposited by selenization of Cu and Sn grow in the Cu2Se and SnSe2 phases, respectively. The effect of deposition temperature and Cu/Se mass ratio on the transport properties of Cu2ZnSnSe4 films was analyzed. The electrical behavior of the compound was studied.
... Будущее развитие тонкопленочной фотовольтаики зависит от создания дешевых и технологичных методов осаждения полупроводниковых нетоксичных соединений, которые используются как эффективные абсорберы света в солнечных элементах [1][2][3]. К таким соединениям относится четырехкомпонентный материал Cu 2 ZnSnSе 4 , со структурой кестерита [4]. Благодаря многим преимуществам, включающим низкую токсичность, не высокую стоимость и распространенность в земной коре его составляющих, Cu 2 ZnSnSе 4 считается более пригодным для массового производства. ...
There were results of analysis of Cu2ZnSnSe4 films, which is a solar cell of the
future, and showed the advantages of their receipt by electrodeposition. Cu2ZnSnSe4
electroplating process was performed on the molybdenum electrode in potentiostatic mode
from electrolyte based on tartaric acid containing ions of Cu2+, Zn2+ and Sn4+ (pH~1,5).
The optimal electrolysis mode for precipitating Cu2ZnSnSe4 compounds with stoichiometric
composition is E = -0,6V. Cu2ZnSnSe4 precipitations were obtained with a uniform
distribution over the substrate surface. The films had a composition close to a stoichiometric
composition (atomic %): Cu = 19,5 ± 0,2; Zn = 10,6 ± 0,5; Sn = 14,6 ± 0,4; Se =
=55,2 ± 1,1. The as-precipitated films have a rough surface and formed from large particle
size of 2.1 microns, which are composed of small spherical particles with an average size
of 200÷500 nm. The smallest spherical particles diameter is 25 nm, they fit snugly
together and become larger in the form of grains of different shapes with increasing
deposition time.
... Recent investigations have analyzed the characteristics of the quaternary materials based on Cu, Zn, Sn, S, and/or Se (CZTS, Se) [4][5][6][7][8], in which In or Ga atoms are replaced by Zn and Sn [9], and through controlled growth processes, Kesterite type structures can be obtained (space group ) and stannite (space group ) [10]. Several studies have focused on both the optical properties and the diffusion of metals forming Kesterite type structure; studies developed by selenization processes [11][12][13]; morphological analysis by varying the order of deposition precursors (masses and sequences deposition by co-evaporation) [14,15] and the effects that different temperatures and pressures used in the growth of CZTSe polycrystalline samples [16] and secondary phases formation [17,18] to analyze chemical composition, internal and surface morphology, crystal structure, electrical transport mechanisms and conductivity type [19,20]. There is uncertainty in the values of interest of some properties found in the CZTSe. ...
We demonstrate experimental data to elucidate the reason for the discrepancies of reported band gap energy (Eg) of Cu2ZnSnSe4 (CZTSe) thin films, i.e., 1.0 or 1.5 eV. Eg of the coevaporated CZTSe film synthesized at substrate temperature (Tsub) of 370 °C, which was apparently phase pure CZTSe confirmed by x-ray diffraction (XRD) and Raman spectroscopy, is found to be around 1 eV regardless of the measurement techniques. However, depth profile of the same sample reveals the formation of ZnSe at CZTSe/Mo interface. On the other hand, Eg of the coevaporated films increases with Tsub due to the ZnSe formation, from which we suggest that the existence of ZnSe, which is hardly distinguishable from CZTSe by XRD, is the possible reason for the overestimation of overall Eg.
Cu2ZnSnSe4 (CZTSe) thin films are grown by coevaporation. Composition depth profiles reveal that a Zn rich phase is present at the CZTSe/Mo interface. Raman measurements on the as grown films are used to study the near surface region and the CZTSe/Mo interface, after mechanically removing the thin film from the Mo coated glass. These measurements provide direct experimental evidence of the formation of a ZnSe phase at the CZTSe/Mo interface. While the Raman spectra at the surface region are dominated by CZTSe modes, those measured at the CZTSe/Mo interface are dominated by ZnSe and MoSe2 modes.
Despite the success of Cu(In,Ga)Se2 (CIGS) based PV technology now emerging in several industrial initiatives, concerns about the cost of In and Ga are often expressed. It is believed that the cost of those elements will eventually limit the cost reduction of this technology. One candidate to replace CIGS is Cu2ZnSnSe4 (CZTSe).We report the preliminary results of CZTSe thin films grown on bare and Mo coated glass through selenization of DC magnetron sputtered Cu/Zn/Sn precursor layers in an atmosphere of Se vapour. The influence of the selenization temperature on the resulting films has been studied. The resulting films were studied by SEM/EDS, XRD, and Raman scattering.
Cu2ZnSnSe4 (CZTSe) thin film solar cells have been produced via co-evaporation followed by a high-temperature annealing. In order to reduce the decomposition of the CZTSe, a SnSe2 capping layer has been evaporated onto the absorber prior to the high-temperature treatment. This eliminates the Sn losses due to SnSe evaporation. A solar cell efficiency of 5.1% could be achieved with this method. Moreover, the device does not suffer from high series resistance, and the dominant recombination pathway is situated in the absorber bulk. Finally, different illumination conditions (white light, red light, and yellow light) reveal a strong loss in fill factor if no carriers are generated in the CdS buffer layer. This effect, known as red-kink effect, has also been observed in the closely related Cu(In,Ga)Se2 thin film solar cells. Copyright © 2013 John Wiley & Sons, Ltd.
Cu2ZnSnSe4 (CZTSe) thin films were prepared by the simple process of selenization of single-layered metallic Cu-Zn-Sn precursors. These metallic precursors were deposited by radio frequency magnetron sputtering of a ternary Cu-Zn-Sn alloy target. Successive selenization was performed at various temperatures between 250°C and 500°C for 30 min. X-ray diffraction and Raman analysis showed that a single phase of the CZTSe compound can be obtained by selenization at 400°C, while increasing the selenization temperature to 500°C improves the grain size and crystal quality. The direct optical band gap of CZTSe films was calculated to be 1.06 eV to 1.09 eV with a high absorption coefficient on the order of 104 cm−1 for samples selenized at 400°C to 500°C. The obtained films are p-type semiconductors with bulk carrier concentrations of 2.41 to 7.96 × 1018 cm3, mobilities of 1.30 cm2 V−1 s−1 to 9.27 cm2 V−1 s−1, and resistivities of 0.20 Ωcm to 1.95 Ωcm.
Thin films of Cu3BiS3 have been produced by conversion of stacked and co-electroplated Bi–Cu metal precursors in the presence of elemental sulfur vapor. The roles of sulfurization temperature and heating rate in achieving single-phase good quality layers have been explored. The potential loss of Bi during the treatments has been investigated, and no appreciable compositional difference was found between films sulfurized at 550 °C for up to 16 h. The structural, morphological and photoelectrochemical properties of the layers were investigated in order to evaluate the potentials of the compound for application in thin film photovoltaics.
This paper gives an overview of the main research directions in chalcopyrite material research and the application of results for the improvement and fabrication of solar cells. So far the copper indium gallium sulphur selenide material family is the base for the highest efficiency thin-film solar cells and the most advanced in terms of actual commercialisation. The transfer of research results into actual production from its early stage and the development of the chalcopyrite thin-film solar cell industry are sketched. The last part of the review shortly describes a number of current industrial players involved in the manufacturing of chalcopyrite solar cells.
We have developed a fabrication process for integrated submodules using Cu(In,Ga)Se2 (CIGS) absorbers deposited by in-line three-stage evaporation. An in-situ monitoring system for the compositions and thicknesses of the CIGS absorbers was also developed. High-performance CIGS submodules with efficiencies as high as η=15.8% with 17 interconnected cells (aperture area: 76.5cm2) have been fabricated.
Thin films of Bi2S3 with different thicknesses were prepared by the chemical deposition method from an aqueous acidic bath using thiosulfate as a sulfide ion source. The effect of film thickness on the optical, structural and electrical properties was studied. A shift of 0.6 eV in the optical bandgap energy, Eg, and a decrease in electrical resistivity from 2.8 × 104 to 5 × 103 Ω cm and an increase in grain size of Bi2S3 crystallites from 5.2 to 8.0 nm were observed when the thickness was varied from 52.7 to 220 nm. These changes are attributed to the quantum size effect in semiconducting films.
Voltage and Cu/Bi ratio mass dependence of photocurrent was studied in Cu3BiS3 thin films prepared by co-evaporation technique. The intensity dependence of steady state photocurrent (Iph) follows a power law with intensity (F), Iph ∝ Fγ where the power γ is in the range between 0.5 and 1.0, which suggests monomolecular recombination process. Photocurrent signal was found to be decaying as a function of both applied voltage and intensity, initially decreasing at considerably fast rates and later at slower ones due to the continuos distribution of defect states. Additionally, the differential life time constants were calculated. Measurements of temperature effect on conductivity (from 100K to 450K) were carried out. It was found that at temperatures greater than 350K, the conductivity is predominantly affected by transport of free carriers in extended states of the conduction band, whereas in the range of temperatures below 250K, the conductivity is dominated by the VRH (Variable Range Hopping) transport mechanism.
Thin film solar cells with chalcopyrite CuInSe2/Cu(lnGa)Se-2 (CIS/CIGS) absorber layers have attracted significant research interest as an important light-to-electricity converter with widespread commercialization prospects. When compared to the ternary CIS, the quaternary CIGS has more desirable optical band gap and has been found to be the most efficient among all the CIS-based derivatives. Amid various fabrication methods available for the absorber layer, electrodeposition may be the most effective alternative to the expensive vacuum based techniques. This paper reviewed the developments in the area of electrodeposition for the fabrication of the CIGS absorber layer. The difficulties in incorporating the optimum amount of Ga in the film and the likely mechanism behind the deposition were highlighted. The role of deposition parameters was discussed along with the phase and microstructure variation of an as-electrodeposited CIGS layer from a typical acid bath. Related novel strategies such as individual In, Ga and their binary alloy deposition for applications in CIGS solar cells were briefed.
Photovoltaic Energy Conversion
- M Altosaar
- Raudoja
- Timmo
- Danilson
- Grossberg
- Krunks
- E Varema
- Mellikov