Copper Zinc Tin Sulfide Films Research Articles

Optimization of the optoelectronic properties of copper zinc tin sulfide thin films for solar photovoltaic applications

Copper Zinc Tin Sulfide (CZTS), a successful contender for environmentallybenign thin film photovoltaics was successfully prepared on soda-lime glass substrates through an economically feasible nebulizer assisted spray pyrolysis technique. Further, a solar cell structure withn-CdS/p-CZTSheterojunction was fabricated to study the performance of the nebulizer sprayed CZTS absorber layer using different precursor solutions for copper such as copper acetate, copper chloride, and copper nitrate. Investigations were done to ascertain the influence of different copper precursors on the optoelectronic properties of CZTS thin films by systematically analyzing their characteristics determined by using different analytical techniques. X-ray diffraction studies show a preferential orientation along (112) plane for the deposited kesterite film. The obtained film thickness and crystallite size were found to be 507 nm and 8 nm, respectively, for the film derived from copper nitrate based spray solution. AFM morphological analysis also confirmed a higher particle size for copper nitrate based CZTS film whose band gap was found to be 1.50 eV. The absorption characteristic was also in the favor of nitrate form of the copper precursor which shows a higher absorption value in the visible region than the rest of the samples. Its carrier concentration was found to be 8.06 × 1017 cm−3 which is 4 times higher than the rest of the films and mobility was found to be of the order of 12.3 cm2 V−1 s−1. The open circuit voltage, short circuit current, fill factor, and efficiency of copper nitrate based CZTS solar cell structure was found to be better and is determined to be 0.27 V, 2.51 mA cm−2, 24.3%, and 0.165%.

Investigations on post sulphurised Cu2ZnSnS4 absorber layer thin films prepared using radio frequency magnetron sputtering

Copper zinc tin sulfide (CZTS) quaternary semiconductor thin films were prepared using binary sulfur rich sputtering targets - copper sulfide (CuS), zinc sulfide (ZnS), and tin sulfide (SnS) by Radio Frequency Magnetron Sputtering with the stacking sequence CuS/ ZnS/ SnS at a substrate temperature of 300 °C. The films were then subsequently sulphurised at 350 °C in Hydrogen Sulfide atmosphere for 60 min. X-ray diffraction studies carried out on the CZTS films revealed the presence of CZTS kesterite phase along the 〈112〉 and 〈220〉 directions. X- ray diffraction results were validated by Raman spectroscopy. The composition of CZTS thin films were confirmed using X-Ray photoelectron spectroscopy and the atomic percentage of the individual elements were quantitatively estimated. The Valance band spectra and Ultra-violet photoelectron spectroscopy were used to study the electronic properties of the sulphurised CZTS thin films. The optical properties of CZTS thin films were studied using Ultraviolet - visible spectrophotometer and the optical band gap was found to be 1.477 eV. The Hall Effect measurements confirmed the p-type nature of the films and the results are discussed.

Effect of spray volume on the properties of Cu2ZnSnS4 absorber thin film fabricated through nebulizer assisted spray pyrolysis technique

Copper Zinc Tin Sulfide (CZTS) is a growing semiconductor chalcogenide that has the potential to act as an alternative nontoxic absorber for commercial silicon-based devices in the sustainable photovoltaic conversion of solar energy in the near future. A debut attempt was made to economically fabricate this earth-abundant solar absorber thin film through indigenously designed cost-effective nebulizer assisted chemical spray pyrolysis technique without high-temperature annealing. The deposition was carried out at different spray volumes to modify the thickness of the absorber material directly on a bare soda-lime glass substrate and effect of CZTS film thickness on its structural, morphological, optical and electrical properties were studied by using appropriate characterization techniques. The film with a thickness of 740 nm for a precursor spray volume of 12 ml resulted in CZTS film with better energy conversion characteristics.

Structural and optical properties of CZTS nanoparticles prepared by a colloidal process

This research presents the influence of copper (Cu) concentration on the properties of copper zinc tin sulfide (CZTS) nanoparticles (NPs) synthesized by a colloidal method, employing oleylamine as an organic solvent. From the structural analysis, a pure phase of CZTS was obtained at an optimized molar ratio of 1.8:1.1:1:4, and secondary phases were observed as the Cu concentration increased. The increment of the NPs size from 15 to 50 nm was noticed as a function of Cu concentration. Importantly, the optical bandgap energy was tuned from 1.35 to 1.68 eV with respect to Cu concentration. The sample synthesized at the molar ratio of 1.8:1.1:1:4 showed a pure phase CZTS with desired elemental composition and bandgap. Furthermore, CZTS thin films were prepared by a doctor-blade method using synthesized NPs followed by annealing under a sulfur/nitrogen atmosphere. The annealed CZTS film showed a significant improvement in the morphological, electrical and optoelectronic properties. Thus, the annealed CZTS film can be efficiently used as an absorber layer in low-cost thin film solar cells. Synthesis of CZTS nanoparticles by hot injection process at different copper concentration and their impact on the particle size & bandgap.

Structural homogenization and cation ordering in CZTS films during sulfurization as probed via in-situ Raman

In this work, we investigate the production of copper-zinc-tin-sulfide (CZTS) thin films via the sintering of nanoparticle coatings. CZTS nanoparticles are produced via spray pyrolysis starting from a solution of metal salts and thiourea. This approach yields small particles that are easy to disperse and apply onto the desired substrate. Sintering these coatings into large-grained films, however, is not trivial. We have used a sodium disulfide-dipping technique that facilitates large-scale grain growth and high-phase purity after annealing in a sulfur atmosphere. We have also utilized a custom-built apparatus to perform in situ Raman spectroscopy on closed systems in volatile and corrosive environments at high temperatures. With this apparatus, we have observed the growth of long-range-ordered crystal domains at high temperature. We have found that precise control of the cooling rate is highly beneficial for cation ordering in large grain CZTS, and that cation re-ordering and phase re-homogenization in large grain CZTS are possible via low-temperature post-processing. This study highlights the fact that much is still not understood about the kinetics of phase evolution for this complex quaternary system during thermal processing, and that well-designed in-situ characterization techniques are necessary to overcome this fundamental lack of knowledge.

Optical and Electrical Properties of Copper Zinc Tin Sulfide Films As Solar Cell Absorber Materials Prepared by a Compacting Process

The copper zinc tin sulfide (CZTS) thin films are prepared by a promising non vacuum compacting process based on ball milling and coating technique. The results reveal that a well-formed crystalline structure of kesterite CZTS are observed after sintering at 450°C. The optical band gap is 1.49, 1.59, 1.33, and 1.21 eV for the films with Cu/Zn/Sn atomic radio of 1.00 : 0.50 : 0.52, 1.00 : 0.44 : 0.41, 1.00 : 0.60 : 0.49, and 1.00 : 0.49 : 0.58, respectively. The compacting process can further improve the performances of CZTS film. For the CZTS thin film with Cu/Zn/Sn atomic radio of 1.00 : 0.60 : 0.49, the surface morphology of the film is significantly improved by a compacting process applied to the coating films before sintering, and the resistivity decreased from 23.67 to 1.18 Ω cm with the compacting pressure increasing from 0 to 200 MPa at room temperature, which showing a promising application of the compacting process method in fabricating CZTS film for solar cells.

Characterization of single step electrodeposited Cu2ZnSnS4 thin films

Electrodeposited copper zinc tin sulfide (CZTS) thin films grown on conducting glass substrates are investigated in this report. The photoelectrochemical cell (PEC), optical, structural and morphological properties of the deposited films have been characterized. PEC measurements of the CZTS thin film showed p-type electrical conductivity. Optical measurement showed that the transmittance of CZTS films is observed to about 0.5–3.4% in the wavelength range 300–1100 nm. It is also observed that the absorbance of the CZTS thin films rapidly increases in the wavelength range 580–620 nm and then it decreases slowly. The band gap of the CZTS thin film is observed to be in the range 1.6–2.2 eV. The transmittance and band gap decreases upon annealing at different temperatures but the absorbance and the grain size increases due to the improvement of crystalline quality upon annealing. From the X-ray diffraction study, the CZTS films are found to be polycrystalline with (112), (200), (105), (204), (312), (220) orientations of the tetragonal structure. The average crystallite size is estimated to 23 nm for as-deposited film, 26 nm for annealed at 300 °C and 40 nm for annealed at 350 °C. It is found from SEM study that the precursor film shows non-uniform distribution of agglomerated particles with well-defined boundaries. As the annealing temperature increases, the crystallization of the films is observed to improve, and hence the morphology of as-deposited precursor film is observed to change into the larger flat grains upon annealing.

Effect of calcination temperature on the properties of CZTS absorber layer prepared by RF sputtering for solar cell applications

In present work, we report synthesis of nanocrystalline Kesterite copper zinc tin sulfide (CZTS) films by RF magnetron sputtering method. Influence of calcination temperature on structural, morphology, optical, and electrical properties has been investigated. Formation of CZTS has been confirmed by XPS, whereas formation of Kesterite-CZTS films has been confirmed by XRD, TEM, and Raman spectroscopy. It has been observed that crystallinity and average grain size increase with increase in calcination temperature and CZTS crystallites have preferred orientation in (112) direction. NC-AFM analysis revealed the formation of uniform, densely packed, and highly interconnected network of grains of CZTS over the large area. Furthermore, surface roughness of CZTS films increases with increase in calcination temperature. Optical bandgap estimated using UV–Visible spectroscopy decreases from 1.91 eV for as-deposited CZTS film to 1.59 eV for the film calcinated at 400 °C which is quite close to optimum value of bandgap for energy conversion in visible region. The photo response shows a significant improvement with increase in calcinations temperature. The employment these films in solar cells can improve the conversion efficiency by reducing recombination rate of photo-generated charge carriers due to larger grain size. However, further detail study is needed before its realization in the solar cells.

Grain-to-Grain Compositional Variations and Phase Segregation in Copper-Zinc-Tin-Sulfide Films.

We have performed a rigorous investigation of the structure and composition of individual grains in copper-zinc-tin-sulfide (CZTS) films realized by sulfurization of a sputtered metal stack. Although on average close to the ideal CZTS stoichiometry, elemental analysis shows significant grain-to-grain variations in composition. High-resolution Raman spectroscopy indicates that this is accompanied by grain-to-grain structural variations as well. The intensity from the 337 cm(-1) Raman peak, generally assigned to the kesterite phase of CZTS, remains constant over a large area of the sample. On the other hand, signals from secondary phases at 376 cm(-1) (copper-tin-sulfide) and 351 cm(-1) (zinc-sulfide) show significant variation over the same area. These results confirm the great complexity inherent to this material system. Moreover, structural and compositional variations are recognized in the literature as a factor limiting the efficiency of CZTS photovoltaic devices. This study demonstrates how a seemingly homogeneous CZTS thin film can actually have considerable structural and compositional variations at the microscale, and highlights the need for routine microscale characterization in this material system.

Spin-coated kesterite CZTS thin films for photovoltaic applications

Copper zinc tin-sulfide (CZTS) films have been widely studied over recent years due to the inherent advantages of low cost, high absorption coefficient (≥ 104 cm−1), suitable band gap (∼1.5 eV) and nontoxicity. In this work, spin coating was used to obtain CZTS films of various compositions and degrees of crystallization on glass substrates, which were then annealed at 500 °C in a N2 atmosphere by using a rapid thermal processing (RTP) furnace in order to optimize their structure. Non-stoichiometric precursors and low spinning speeds resulted in a lower sheet resistance, which is considered to be a result of lower degree of crystallization. Furthermore, the non-stoichiometric films had a high optical band gap (> 1.66 eV) whereas the band gap of the stoichiometric films (1.4 to 1.6 eV) was close to the optimal value (1.5 eV) for solar-cell applications.

Formation of Copper Zinc Tin Sulfide Thin Films from Colloidal Nanocrystal Dispersions via Aerosol-Jet Printing and Compaction.

A three-step method to create dense polycrystalline semiconductor thin films from nanocrystal liquid dispersions is described. First, suitable substrates are coated with nanocrystals using aerosol-jet printing. Second, the porous nanocrystal coatings are compacted using a weighted roller or a hydraulic press to increase the coating density. Finally, the resulting coating is annealed for grain growth. The approach is demonstrated for making polycrystalline films of copper zinc tin sulfide (CZTS), a new solar absorber composed of earth-abundant elements. The range of coating morphologies accessible through aerosol-jet printing is examined and their formation mechanisms are revealed. Crack-free albeit porous films are obtained if most of the solvent in the aerosolized dispersion droplets containing the nanocrystals evaporates before they impinge on the substrate. In this case, nanocrystals agglomerate in flight and arrive at the substrate as solid spherical agglomerates. These porous coatings are mechanically compacted, and the density of the coating increases with compaction pressure. Dense coatings annealed in sulfur produce large-grain (>1 μm) polycrystalline CZTS films with microstructure suitable for thin-film solar cells.

Interfacial Properties of CZTS Thin Film Solar Cell

Cu-deficient CZTS (copper zinc tin sulfide) thin films were grown on soda lime as well as molybdenum coated soda lime glass by reactive cosputtering. Polycrystalline CZTS film with kesterite structure was produced by annealing it at 500°C in Ar atmosphere. These films were characterized for compositional, structural, surface morphological, optical, and transport properties using energy dispersive X-ray analysis, glancing incidence X-ray diffraction, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, UV-Vis spectroscopy, and Hall effect measurement. A CZTS solar cell device having conversion efficiency of ~0.11% has been made by depositing CdS, ZnO, ITO, and Al layers over the CZTS thin film deposited on Mo coated soda lime glass. The series resistance of the device was very high. The interfacial properties of device were characterized by cross-sectional SEM and cross-sectional HRTEM.

Substrate and temperature dependence of the formation of the Earth abundant solar absorber Cu2ZnSnS4 by ex situ sulfidation of cosputtered Cu-Zn-Sn films

Copper zinc tin sulfide (CZTS) thin films were synthesized by ex situ sulfidation of Cu-Zn-Sn metal alloy precursor films cosputtered from Cu, Cu-Zn, and Cu-Sn targets onto five different substrate materials: single crystal quartz, fused quartz, sapphire, Pyrex, and soda lime glass (SLG). Cosputtered precursor films, which were found to consist of Cu, Zn, and Sn metals and Cu6.26Sn5 ordered alloys, were sulfidized between 100 and 600 °C, corresponding to an S pressure range of 0.051–36 Torr. While CZTS forms at temperatures as low as 300 °C on all substrates, the film's phase composition is dominated by binary metal sulfides between 300 and 400 °C. Significant phase composition variations among films synthesized on different substrates begin to emerge at 400 °C. Films grown on SLG are nearly phase pure CZTS by 500 °C, with small amounts of ZnS. In contrast, films deposited on all other substrates persistently contain significant amounts of impurity phases such as SnS2 and Cu4Sn7S16 until the sulfidation temperature is increased to 600 °C. Significant grain growth also begins between 500 and 600 °C. At 600 °C, CZTS films synthesized on SLG were found to have significantly larger grains than films grown on any of the other substrates. These results demonstrate that CZTS phase purity and grain size, properties that may affect solar cell performance, are affected by impurity diffusion from the SLG substrate, further emphasizing the importance of selecting appropriate substrates.

Thermal treatments and characterization of CZTS thin films deposited using nanoparticle ink

The structural, optical, and optoelectronic properties of copper zinc tin sulfide (CZTS) films, deposited by a nonvacuum nanoparticle based approach were studied as a function of different annealing temperatures. The CZTS films for photovoltaic applications were deposited using the doctor blading method using an ink prepared with nanoparticles synthesized using the solvothermal method. Deposited films were annealed at different temperatures in N2–S atmosphere. The films were characterized using different tools such as X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), ultraviolet–visible spectroscopy, Raman spectroscopy, and photoconductivity. The results showed that the kesterite phase was formed in the temperature range between 400 and 550 °C. At temperatures beyond 500 °C, many peaks of binary and ternary phases were detected, probably because of the decomposition of the kesterite layer. The cross section SEM images showed that the film is compact; however, there are isolated voids. The EDXS estimated chemical composition was found to vary with annealing temperature; the nearly stoichiometric film was obtained when annealed at 450 °C. The optical band gap of the stoichiometric film was 1.6 eV, and it showed photoconductivity.

Alkali-metal-enhanced grain growth in Cu2ZnSnS4 thin films

Copper zinc tin sulfide (CZTS) is an emerging photovoltaic material comprised of earth abundant elements. Presence of very small amounts of sodium and potassium during the synthesis of thin CZTS films enhances grain growth and leads to microstructures ideally suited for solar cells.

International Conference on Solar Energy Photovoltaics

Worldwide, the interest in photovoltaics as an energy technology as well as an industrial opportunity has increased significantly within the last few years, and with the launch of Jawaharlal Nehru National Solar Mission (JNNSM) it has created a lot of interest in the Indian solar sector. To create demand and attract investment in the sector, the government is providing various incentives. India has a huge potential for solar PV and with the right policy support by the Indian Government, India can become a major player in the solar market globally. The conference was a great success, having 3 keynote lectures, 5 plenary lectures, 12 invited lectures, and 90 contributed papers.The conferencewas inaugurated byMr. Arun Kumar Sahoo, Minister of State, Energy, and I&PR, Government of Odisha, India who emphasizes on energy Security. The guest of honour, Padma Shri Professor A. K. Barua, discussed the status and prospects of solar photovoltaics in India. The conference mainly focuses on device aspects of photovoltaic, involving nearly all the area with a special session on plasmonics and nanostructerd solar cells. The selected papers for this special issue are representative of the presentation/deliberation during the International Conference on Solar Energy Photovoltaic held at KIIT University, Bhubaneswar, India from 19th to 21st December, 2012. The special issue has papers focused on alternative buffer layer for polycrystalline thin film solar cells to replace CdS (cadmium sulfide). The focused materials were SnS (tin sulfide) and In 2 S 3 (indium sulfide). Few articles emphasize the use of transparent conducting oxide (TCO) for the hybrid and organic solar cell applications. Recently, the focus has been shifted to the use of cheap and abundant elements that make CZTS (copper zinc tin sulfide) as a promising alternative to current solar cells [1, 2]. Few papers have discussed the preparation of CZTS film using low-cost techniques. Some articles discuss the formation of nanoinks and nanopartilces of CIS (copper indium selenide) and CdSe. The conference was well supported by the Department of Science and Technology (DST) through its Solar Energy Research Initiative Program, Defence Research and Development Organization (DRDO), Indian Space Research Organization (ISRO), and Hind High Vacuum Pvt. Ltd. Special thanks go to the Founder of KIIT University, Dr. Achutya Samantawho has encouraged and guided us tomake this conference a great success.

Porous copper zinc tin sulfide thin film as photocathode for double junction photoelectrochemical solar cells

Porous copper zinc tin sulfide (CZTS) thin film was prepared via a solvothermal approach. Compared with conventional dye-sensitized solar cells (DSSCs), double junction photoelectrochemical cells using dye-sensitized n-type TiO(2) (DS-TiO(2)) as the photoanode and porous p-type CZTS film as the photocathode shows an increased short circuit current, external quantum efficiency and power conversion efficiency.