Cu2ZnSnSe4 Thin Film Research Articles

In situXRD investigation of Cu2ZnSnSe4thin film growth by thermal co-evaporation

The deposition of a Cu2ZnSnSe4 (CZTSe) thin film with a multi-stage co-evaporation process is investigated with time-resolved in situ X-ray diffraction (in situ XRD). For the experiment a novel setup intended for in situ analysis of thin film deposition processes was used. The in situ data confirm the former observation that CZTSe growth is delayed with deposition of only Cu2−xSe and ZnSe in the initial process stage and provide new insight into the evolution of the appearing phases. In Zn-rich deposition conditions, ZnSe deposited at the beginning may not be consumed by the growing CZTSe but remain as an unreacted layer at the interface to the Mo back contact. Cu2−xSe growth starts with the formation of a Cu rich phase, which is reduced to a Cu poor phase in the process. Furthermore, our results show that in situ XRD at elevated temperatures is able to distinguish between ZnSe and CZTSe and that it can be used for the detection of ZnSe as secondary phase.

Cu2ZnSnSe4 thin films prepared by selenization of precursor evaporated from Cu2ZnSnSe4 and Na2Se

ABSTRACTCu2ZnSnSe4 thin films were prepared by using the synthesized Cu2ZnSnSe4 ingot and Na2Se powder at various Na2Se/Cu2ZnSnSe4 mole ratio as evaporation materials for selenization process. From EPMA analysis, the composition was approximately constant even if the Na2Se/Cu2ZnSnSe4 mole ratio increased. X-ray diffraction studies revealed that the thin films had a kesterite Cu2ZnSnSe4 structure and the foreign phases disappeared with increasing the Na2Se/Cu2ZnSnSe4 mole ratio. The Na2Se addition enhanced to grow thin films having a close-packed structure and columnar grains. The values of Voc and Isc in Cu2ZnSnSe4 thin film solar cells increased with increasing the Na2Se/Cu2ZnSnSe4 mole ratio.

Antimony-Based Ligand Exchange To Promote Crystallization in Spray-Deposited Cu2ZnSnSe4 Solar Cells

A multistrategy approach to overcome the main challenges of nanoparticle-based solution-processed Cu2ZnSnSe4 thin film solar cells is presented. We developed an efficient ligand exchange strategy, using an antimony salt, to displace organic ligands from the surface of Cu2ZnSnS4 nanoparticles. An automated pulsed spray-deposition system was used to deposit the nanoparticles into homogeneous and crack-free films with controlled thickness. After annealing the film in a Se-rich atmosphere, carbon-free and crystalline Cu2ZnSnSe4 absorber layers were obtained. Not only was crystallization promoted by the complete removal of organics, but also Sb itself played a critical role. The Sb-assisted crystal growth is associated with the formation of a Sb-based compound at the grain boundaries, which locally reduces the melting point, thus promoting the film diffusion-limited crystallization.

Cu2ZnSnSe4 thin film solar cells prepared by rapid thermal annealing of co-electroplated Cu–Zn–Sn precursors

Cu2ZnSnSe4 (CZTSe) thin films were prepared by selenization of co-electrodeposited Cu–Zn–Sn precursors, which were electrodeposited on Mo-coated glass substrates in one-step process. Two annealing processes, rapid thermal annealing (RTA) and conventional furnace annealing (CFA), were carried out for selenizing the precursors at 500°C. The structure and morphology of the CZTSe thin films were characterized using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). It is found that the RTA process benefits the formation of single phase CZTSe absorbers with large grains and the energy band gap of CZTSe film is 0.98eV. Photovoltaic cells with the structure of glass/Mo/CZTSe/CdS/i-ZnO/ZnO:Al were fabricated using the RTA–CZTSe films as absorbers. The highest efficiency of 4.5% so far for a co-electrodeposited CZTSe solar cell was achieved.

Preparation of Cu2ZnSnSe4 thin films by selenization of precursor evaporated from Cu2ZnSnSe4 compound

AbstractCu2ZnSnSe4 ingot was synthesized and then used as a precursor for selenization process in order to fabricate Cu2ZnSnSe4 thin films. The thin films were prepared at each point A‐F in our selenization process and their properties were investigated. Cu2ZnSnSe4 ingot and thin films had a kesterite Cu2ZnSnSe4 structure. From EPMA analysis and XRD studies, the mechanism of Cu2ZnSnSe4 formation was discussed. Cu‐Se phases were related to Cu2ZnSnSe4 formation. Cu2ZnSnSe4 may decompose to Sn‐Se compound during the annealing process at 550 oC. Cu2ZnSnSe4 thin film solar cells demonstrated Voc=300 mV, Isc=7.25 mA/cm2. The band gap energy of Cu2ZnSnSe4 thin film determined from the QE spectra estimated to be approximately 1.04 eV. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication of Cu2ZnSnSe4 thin films from an electrodeposited Cu‐Zn‐Sn‐Se/Cu‐Sn‐Se bilayer

AbstractIn this study, a novel sequential electrodeposition of Cu‐Zn‐Sn‐Se and Cu‐Sn‐Se layers was applied for fabrication of a Cu2ZnSnSe4 (CZTSe) thin film. The desired Cu‐Zn‐Sn‐Se/Cu‐Sn‐Se bilayer was obtained at a selected applied potential from electrolytes containing corresponding metal and selenium ions. Annealing of the bilayer film under argon (Ar) flow induced significant losses of Sn and Se components due probably to evaporation of the SnSe compound. Suppression of these losses could be realized by introduction of Se vapor during the annealing: as a result, a CZTSe thin film with an ideal Cu‐poor/Zn‐rich composition for solar cell application was obtained. The solar cell with a device with the structure of glass/Mo/CZTSe/CdS/ZnO/AZO derived from thus‐obtained CZTSe film exhibited a conversion efficiency of 1.1%, while the device still possessed a significant leakage current and a high series resistance. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of selenization on sprayed Cu2ZnSnSe4 thin film solar cell

We made Cu2ZnSnSe4 (CZTSe) thin film solar cell using spray pyrolysis. The photo-absorber CZTSe was fabricated by post-selenization of sprayed Cu2ZnSnS4 (CZTS) film, and In2S3, which was adapted as a buffer layer, was also deposited by spray pyrolysis. The sprayed CZTS films were annealed at 530°C for 15min and 25min in Se vapor ambient, and through the selenization CZTS films were converted to CZTSe films. These re-crystallized CZTSe films were used as the photo-absorber of solar cell. Conversion efficiency of 2.39% was obtained with 25min annealed CZTSe, whereas 0.27% conversion efficiency was obtained with 15min annealed one. By comparing characterization results for both solar cells, it might be concluded that the conversion efficiency was dominated by the selenization condition of the photo-absorber layer which affected crystal quality of the photo-absorber.

Cu2ZnSnSe4 thin film solar cells based on a single-step co-evaporation process

Cu2ZnSnSe4 (CZTSe) thin films were deposited on Mo-coated soda–lime glass substrates by single-stage co-evaporation process and the effect of substrate temperature (Tsub) was investigated on the CZTSe thin film growth during the process. The film thickness decreased and the grain size increased with increasing Tsub. The optimum substrate temperature to obtain CZTSe films was found to be 593K. The film grown at Tsub of 773K seems to have the phase decomposition into CuxSe and ZnSe, probably because of Sn loss during the process. The best cell fabricated with a CZTSe absorber layer grown at Tsub of 593K produced 2.88% of conversion efficiency.

The Cu2ZnSnSe4 thin films solar cells synthesized by electrodeposition route

An electrodeposition route for preparing Cu2ZnSnSe4 thin films for thin film solar cell absorber layers is demonstrated. The Cu2ZnSnSe4 thin films are prepared by co-electrodeposition Cu–Zn–Sn metallic precursor and subsequently annealing in element selenium atmosphere. The structure, composition and optical properties of the films were investigated by X-ray diffraction (XRD), Raman spectrometry, energy dispersive spectrometry (EDS) and UV–VIS absorption spectroscopy. The Cu2ZnSnSe4 thin film with high crystalline quality was obtained, the band gap and absorption coefficient were 1.0eV and 10−4cm−1, which is quite suitable for solar cells fabrication. A solar cell with the structure of ZnO:Al/i-ZnO/CdS/Cu2ZnSnSe4/Mo/glass was fabricated and achieved an conversion efficiency of 1.7%.

Dielectric function spectra and critical-point energies of Cu2ZnSnSe4 from 0.5 to 9.0 eV

We present dielectric function ɛ = ɛ1 + iɛ2 spectra and critical-point energies of Cu2ZnSnSe4 determined by spectroscopic ellipsometry from 0.5 to 9.0 eV. We reduce artifacts from surface overlayers to the maximum extent possible by performing chemical-mechanical polishing and wet-chemical etching of the surface of a Cu2ZnSnSe4 thin film. Ellipsometric data are analyzed by the multilayer model and the ɛ spectra are extracted. The data exhibit numerous spectral features associated with critical points, whose energies are obtained by fitting standard lineshapes to second energy derivatives of the data. The experimental results are in good agreement with the ɛ spectra calculated within the GW quasi-particle approximation, and possible origins of the pronounced critical-point structures are identified.