Kesterite CZTS Research Articles

Wurtzite copper-zinc-tin sulfide as a superior counter electrode material for dye-sensitized solar cells

Wurtzite and kesterite Cu2ZnSnS4 (CZTS) nanocrystals were employed as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). Compared to kesterite CZTS, the wurtzite CZTS exhibited higher electrocatalytic activity for catalyzing reduction of iodide electrolyte and better conductivity. Accordingly, the DSSC with wurtzite CZTS CE generated higher power conversion efficiency (6.89%) than that of Pt (6.23%) and kesterite CZTS (4.89%) CEs.

Rational Defect Passivation of Cu2ZnSn(S,Se)4 Photovoltaics with Solution-Processed Cu2ZnSnS4:Na Nanocrystals

An effective defect passivation route has been demonstrated in the rapidly growing Cu2ZnSn(S,Se)4 (CZTSSe) solar cell device system by using Cu2ZnSnS4:Na (CZTS:Na) nanocrystals precursors. CZTS:Na nanocrystals are obtained by sequentially preparing CZTS nanocrystals and surface decorating of Na species, while retaining the kesterite CZTS phase. The exclusive surface presence of amorphous Na species is proved by X-ray photoluminescence spectrum and transmission electron microscopy. With Na-free glasses as the substrate, CZTS:Na nanocrystal-based solar cell device shows 50% enhancement of device performance (∼6%) than that of unpassivated CZTS nanocrystal-based device (∼4%). The enhanced electrical performance is closely related to the increased carrier concentration and elongated minority carrier lifetime, induced by defect passivation. Solution incorporation of extrinsic additives into the nanocrystals and the corresponding film enables a facile, quantitative, and versatile approach to tune the defect property of materials for future optoelectronic applications.

Facile synthesis and post-processing of eco-friendly, highly conductive copper zinc tin sulphide nanoparticles

Cu2ZnSnS4 (CZTS) nanoparticles have shown promising properties to be used as an energy harvesting material. They are usually synthesised under inert atmosphere or vacuum, whereas the subsequent step of film formation is carried out under an atmosphere of sulphur and/or Sn in order to avoid the decomposition of CZTS nanoparticles into binary and ternary species as well as the formation of the corresponding oxides. In the present paper we show that both the synthesis of CZTS nanoparticles and the film formation from the corresponding suspension can be considerably simplified. Namely, the synthesis can be carried out without controlling the atmosphere, whereas during the film annealing a nitrogen atmosphere is sufficient to avoid the depletion of the CZTS kesterite phase. Furthermore, an integrated approach including in-depth Raman analysis is developed in order to deal with the challenges associated with the characterization of CZTS nanoparticles in comparison to bulk systems. The formation of competitive compounds during the synthesis such as binary and ternary sulphides as well as metal oxides nanoparticles is discussed in detail. Finally, the as-produced films have ten times higher conductivity than the state of the art.

Investigation of vulcanization of non-crystalline Cu2ZnSnS4 nano-particles

Non-crystalline Cu2ZnSnS4(CZTS) nano-particles were fabricated by hydrothermal method. CZTS nano-particles that have different Cu/(Zn+Sn) ratio (0.77, 0.89, 1.02) were separately prepared. The morphology, composition and crystal structure of the as-prepared nano-particles and the vulcanized films were investigated by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffractometry, and Raman spectroscopy. When the temperature and time of vulcanization exceeded 400°C and 60min, respectively, the Cu-rich phase (Cu3SnS4) emerged. Sn lost during vulcanization. CZTS sample with 0.77 Cu content (Cu/(Zn+Sn) =0.77) showed pure kesterite CZTS without secondary phases when they were vulcanized at 400°C for 60min.

Effects of Sputter Deposition Sequence and Sulfurization Process of Cu, Zn, Sn on Properties of Cu2ZnSnS4 Solar Cell Material

The effect of a sputter deposition sequence of Cu, Zn, and Sn metal layers on the properties of <TEX>$Cu_2ZnSnS_4$</TEX> (CZTS) was systematically studied for solar cell applications. The set of Cu/Sn/Zn/Cu multi metal films was deposited on a Mo/<TEX>$SiO_2$</TEX>/Si wafer using dc sputtering. CZTS films were prepared through a sulfurization process of the Cu/Sn/Zn/Cu metal layers at <TEX>$500^{\circ}C$</TEX> in a <TEX>$H_2S$</TEX> gas environment. <TEX>$H_2S$</TEX> (0.1%) gas of 200 standard cubic centimeters per minute was supplied in the cold-wall sulfurization reactor. The metal film prepared by one-cycle deposition of Cu(360 nm)/Sn(400 nm)/Zn(400 nm)/Cu(440 nm) had a relatively rough surface due to a well-developed columnar structure growth. A dense and smooth metal surface was achieved for two- or three-cycle deposition of Cu/Sn/Zn/Cu, in which each metal layer thickness was decreased to 200 nm. Moreover, the three-cycle deposition sample showed the best CZTS kesterite structures after 5 hr sulfurization treatment. The two- and three-cycle Cu/Sn/Zn/Cu samples showed high-efficient photoluminescence (PL) spectra after a 3 hr sulfurization treatment, wheres the one-cycle sample yielded poor PL efficiency. The PL spectra of the three-cycle sample showed a broad peak in the range of 700-1000 nm, peaked at 870 nm (1.425 eV). This result is in good agreement with the reported bandgap energy of CZTS.

Effect of Growth Parameters and Annealing Atmosphere on the Properties of Cu2ZnSnS4Thin Films Deposited by Cosputtering

Cu2ZnSnS4(CZTS) thin films were deposited using the cosputtering technique. The growth parameters, such as working pressure, target powers, and postannealing atmosphere, were optimized for CZTS films deposition. A comparative study between post annealing using sulfur vapor in a quartz tube furnace and sulfurization chamber using H2S gas was carried out to optimize the kesterite Cu2ZnSnS4phase. 10 min annealing at 530°C in the furnace in sulfur vapor eliminated all the secondary phases and formed kesterite Cu2ZnSnS4. The diffusion of sulfur in the film during the annealing process enhanced the crystallinity of the film. The kesterite Cu2ZnSnS4phase was confirmed by X-ray diffraction, Raman scattering, and optical measurements. The film showed phonon peaks corresponding to the kesterite CZTS, high-absorption coefficient (1.1 × 105 cm−1), and desired optical direct band gap (1.5 eV).

Synthesis of Pure Metastable Wurtzite CZTS Nanocrystals by Facile One-Pot Method

In this article, pure phase metastable wurtzite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) were synthesized by a facile one-pot method. When pure 1-dodecanethiol (DDT) was used as the solvent, two coexisting CZTS phases (wurtzite and kesterite) were found. When an increased amount of oleylamine (OAm) was added to DDT, kesterite CZTS disappeared gradually, and the as-obtained CZTS NCs became smaller and more uniform. When 0.5 mL of OAm was added, rice-like pure phase metastable wurtzite CZTS NCs were obtained. The factors, including amount of OAm, reaction temperature, reaction time, and concentration of precursors, which influence the morphology, size, and monodispersity of CZTS NCs, were studied in detail. The results showed OAm played an important role in the formation of the final pure phase metastable wurtzite NCs. Time-dependent experiments were performed to observe the growth of CZTS NCs. The final CZTS NCs evolved from spherical-like Cu2S NCs through rhombus-like intermediate shaped NCs to rice-like pure ...

Wet chemical route to the synthesis of kesterite Cu2ZnSnS4 nanocrystals and their applications in lithium ion batteries

Sn-based quaternary material, Cu2ZnSnS4 (CZTS), was successfully synthesized using an inexpensive and quick wet chemical route. The obtained CZTS nanocrystals were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) techniques. XRD and SAED results revealed that kesterite CZTS was formed. The formed CZTS nanocrystals were slightly irregularly faceted particles with diameters between 5nm and 25nm. CZTS was studied as an anode material in rechargeable lithium ion battery for the first time. The Cu2ZnSnS4 annealed at 500°C showed a capacity of about 540mAhg−1 at the initial stage. The first cycle of the CZTS electrode exhibited enormously irreversible capacity. The result indicated that the formation of metallic Sn from the Cu2ZnSnS4 powder was similar to the case in SnO2 or SnS2 electrodes. Cu2ZnSnS4 was demonstrated to be one of the possible candidates of the anode materials for future lithium ion battery.

GROWTH OF Cu2ZnSn(S,Se)4 THIN FILMS BY A SIMPLE ECO-FRIENDLY SOLUTION ROUTE METHOD

A simple and hydrazine-free solution-based approach for depositing Cu2ZnSnS4 (CZTS) and Cu2ZnSn(S,Se)4 (CZTSSe) absorber layers is reported. The process involves incorporating metal salts (Cu(CH3COO)2, Zn(CH3COO)2, SnCl2) and thiourea into a single pyridine-based solution, spin-coating a precursor film, and sulfurizing with sulfur powders or selenizing using Se pellets in an inert atmosphere, to form the desired CZTS or CZTSSe films. X-ray diffraction and Raman spectra studies show that kesterite CZTS and CZTSSe are formed after sulfurization and selenization, respectively. The selenized CZTSSe displays higher crystallinity than the sulfurized CZTS. Photovoltaic devices (glass/ Mo /CZTSSe/ CdS /i- ZnO /n- ZnO /A) employing the solution precursor selenized at 500°C have yielded power conversion efficiency of 1.44% under AM 1.5 illumination.

A facile and low cost synthesis of earth abundant element Cu2ZnSnS4 (CZTS) nanocrystals: Effect of Cu concentrations

Cu2ZnSnS4 (CZTS) nanocrystals (NCs) were synthesized by sulfurization of microwave assisted precursor powders without toxic chemicals. The effects of different Cu concentration from 0.01 to 0.025M on the structural, morphological, compositional, chemical and optical properties of CZTS NCs were investigated. X-ray diffraction patterns, X-ray photoelectron spectroscopy and transmission electron microscopy results showed that the precursor powder contains several broad peaks that could not be assigned to CZTS, ZnS, Cu2-xS, Sn2S3 and Cu2SnS3. However, the sulfurized NCs showed both kesterite CZTS and Cu- and Sn-based secondary phases except for that formed at Cu concentration of 0.02M. Inductively coupled plasma (ICP) results showed that the presence of Cu in the sulfurized CZTS NCs increased with increasing Cu concentration from 16.57 to 32.94at.% while Zn and Sn in the sulfurized CZTS NCs decreased with increasing Cu concentration. UV–Vis spectroscopy results showed that the absorption coefficient of the sulfurized NCs was over 104cm−1 in the visible region and band gap energy of the sulfurized CZTS NCs decreased from 1.65 to 1.28eV with increasing Cu concentration.

Vibrational properties of stannite and kesterite type compounds: Raman scattering analysis of Cu2(Fe,Zn)SnS4

This work reports the analysis of the vibrational properties of stannite–kesterite Cu2(Fe,Zn)SnS4 compounds that has been performed by Raman scattering measurements. The detailed analysis of the experimental spectra has allowed determining the frequency and symmetry assignment of the main and weaker peaks from both stannite Cu2FeSnS4 (CFTS) and kesterite Cu2ZnSnS4 (CZTS) phases. The measurements performed in the kesterite CZTS samples have also revealed the presence of local inhomogeneities that are characterised by an additional peak in the spectra at about 331cm−1. This peak has been related to the presence in these local regions of a high degree of disorder in the cation sublattice, in agreement with previous neutron diffraction analysis in similar samples. Finally, the spectra from the solid solution alloys show a one-mode behaviour of the main A/A1 peak with the chemical composition.

Development of Kesterite Cu2ZnSn(S1-x,Sex)4 (CZTSS)-Based Thin Film Solar Cells with In and Ga Free Absorber Materials

Chalcogenide-based semiconductors, such as CuInSe2, CuGaSe2, Cu(In,Ga)Se2 (CIGS), and CdTe have attracted considerable interest as efficient materials in thin film solar cells (TFSCs). Currently, CIGS and CdTe TFSCs have demonstrated the highest power conversion efficiency (PCE) of over 11% in module production. However, commercialized CIGS and CdTe TFSCs have some limitations due to the scarcity of In, Ga, and Te and the environmental issues associated with Cd and Se. Recently, kesterite CZTS, which is one of the In- and Ga- free absorber materials, has been attracted considerable attention as a new candidate for use as an absorber material in thin film solar cells. The CZTS-based absorber material has outstanding characteristics such as band gap energy of 1.0 eV to 1.5 eV, high absorption coefficient on the order of 104cm-1, and high theoretical conversion efficiency of 32.2% in thin film solar cells. Despite these promising characteristics, research into CZTS-based thin film solar cells is still incomprehensive and related reports are quite few compared to those for CIGS thin film solar cells, which show high efficiency of over 20%. The recent development of kesterite-based CZTS thin film solar cells is summarized in this work. The new challenges for enhanced performance in CZTS thin films are examined and prospective issues are addressed as well.

Earth-abundant non-toxic Cu2ZnSnS4 thin films by direct liquid coating from metal–thiourea precursor solution

A simple process for deposition of pure CZTS films from a methanolic solution of metal–thiourea complex is described. The precursor films are thermolysed at 200°C in air for 10min. Formation of kesterite CZTS is confirmed by X-ray diffraction (XRD). The films have grains of 100–200nm and rms roughness of 1–2nm. The energy band gap of CZTS films is 1.4eV and is p-type in nature with electrical conductivity of 0.5S/cm and thermo electric power coefficient of 86μV/K. The films are photoconducting.

Phase selective synthesis of metastable orthorhombic Cu2ZnSnS4

Cu2ZnSnS4 (CZTS) is acknowledged as an alternative to traditional p-type semiconductors. Traditionally obtained CZTS, however, is mostly kesterite or stannite phase, which features a tetragonal crystal cell. Herein, novel orthorhombic CZTS has been synthesized via an ethylenediamine-assisted hydrothermal method. Ethylenediamine plays an important part in the construction of the orthorhombic phase. Kesterite CZTS was also obtained in an ultrapure water system without ethylenediamine. The structure was confirmed by XRD, XPS and HRTEM. The band gap of the orthorhombic CZTS is about 1.45 eV, which approaches the optimum value for solar photoelectric conversion. What's more, we found that this orthorhombic CZTS is metastable. After annealing at 500 °C, a phase transformation from the orthorhombic structure to the tetragonal kesterite structure was achieved. The photoelectric response was also characterised, which demonstrated its potential for application in photovoltaic devices.

A facile and low-cost synthesis of promising absorber materials on Cu2ZnSn(Sx,Se1−x)4 nanocrystals consisting of earth abundant elements with tunable band gap characteristics

In this paper, we report a facile, low cost synthesis and characterization of kesterite Cu2ZnSn(Sx,Se1−x)4 (CZTSSe) nanocrystals (NCs) by a two-step process involving a solution-based precursor and a post-annealing route. The effects of different Se vaporization temperatures, ranging from 350 °C to 550 °C, on the structural, chemical, compositional, and optical properties of CZTSSe NCs were investigated. X-ray diffraction patterns, Raman spectroscopy, and transmission electron microscopy results indicated that the precursor powder showed several broad peaks that could not be assigned to Cu2ZnSnS4 (CZTS), ZnS, Cu2−xS, Sn2S3 and Cu2SnS3. However, the post-annealed NCs with and without Se vaporization were a single kesterite CZTS phase without a secondary phase. UV-vis spectroscopy results showed that the absorption coefficients of all the post-annealed NCs were over 104 cm−1 in the visible region, and the optical band gap energy decreased systematically from 1.46 eV to 1.14 eV with increasing Se vaporization temperatures.

Fabrication of Cu2ZnSnS4nanowires and nanotubes based on AAO templates

Cu2ZnSnS4 nanowires and nanotubes have been synthesized via a modified sol–gel solution approach with AAO templates. The prepared nanowires and nanotubes have been characterized and show the typical morphology of nanostructure and properties of kesterite CZTS, which can provide the potential application and research for low-dimension solar cells.

Grain Size and Texture of Cu2ZnSnS4 Thin Films Synthesized by Cosputtering Binary Sulfides and Annealing: Effects of Processing Conditions and Sodium

We investigate the synthesis of kesterite Cu2ZnSnS4 (CZTS) polycrystalline thin films using cosputtering from binary sulfide targets followed by annealing in sulfur vapor at 500 {\deg}C to 650 {\deg}C. The films are the kesterite CZTS phase as indicated by x-ray diffraction, Raman scattering, and optical absorption measurements. The films exhibit (112) fiber texture and preferred low-angle and Sigma3 grain boundary populations which have been demonstrated to reduce recombination in Cu(In,Ga)Se2 and CdTe films. The grain growth kinetics are investigated as functions of temperature and the addition of Na. Significantly, lateral grain sizes above 1 um are demonstrated for samples grown on Na-free glass,demonstrating the feasibility for CZTS growth on substrates other than soda lime glass.

Temperature‐dependent study of the Raman A mode of Cu2ZnSnS4 thin films

AbstractThis temperature‐dependent Raman study of kesterite phase Cu2ZnSnS4 (CZTS) thin film was performed over the temperature range 98–378 K. A detailed qualitative analysis showed that the Raman data for the “A” mode of vibration, the strongest peak for kesterite CZTS films, fit very well to a damped harmonic oscillator (DHO) model. This investigation of temperature‐dependent Raman data shows that the observed frequency shift is due to the cumulative effect of thermal expansion and anharmonicity resulting from a 4‐phonon damping process. The temperature dependence of linewidth is also consistent with the above analysis.

CZTS Monograin Powders and Thin Films

This paper reviews results of studies on different materials and technologies for polycrystalline solar cells conducted at Tallinn University of Technology. Structural properties and defect structure of kesterite CZTS compounds (Cu2ZnSnSe4, Cu2ZnSn(SSe)4) were studied. Influence of selenization parameters of a Zn-Cu-Sn stacked layer on the CZTS layer growth and on the morphology, distribution of elements was analyzed. All the results obtained have been used to optimize the technology of producing solar cell structures in different designs. Cu2ZnSnSe4 and, Cu2ZnSn(SSe)4 based monograin layer solar cells were developed.

Investigation of Cu2ZnSnS4 Formation from Metal Salts and Thioacetamide

Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is a very promising alternative to semiconductors based on Ga or In as solar absorber material. CZTS consists of abundant and cheap elements and in addition it displays very beneficial properties like a high optical absorption coefficient and an ideal band gap for photovoltaic applications. In this contribution, we present the preparation of thin films of copper zinc tin sulfide from metal salts (copper(I) iodide, zinc(II) acetate, and tin(II) chloride) and thioacetamide as sulfur source by a solution-based precursor method. The influence of synthesizing temperatures and concentration of thioacetamide in the precursor solution on the obtained CZTS materials was investigated. X-ray diffraction studies show that kesterite CZTS is formed. Depending on the temperature, nanocrystalline films with primary crystallite sizes from 8 nm (180 °C) up to approximately 150 nm (450 °C) were obtained. The early stages of the CZTS formation were monitored by time-resolved simultan...