Molybdenum Coated Soda Lime Glass Research Articles

Solution phase fabrication of photoactive Cu2BaSnS4 thin films for solar energy harvesting

The quaternary Cu2BaSnS4 (CBTS) is a new class of compound-semiconducting material, recently, emerging as one of the promising materials in the field of photovoltaics and solar water splitting applications. The difference in the electronic properties between the cations in the CBTS structure discourages the antisite defect formation and associated band tailing seen in kesterite Cu2ZnSn(S,Se)4 (CZTSSe) absorber. The direct bandgap, strong optical absorption coefficient (> 104 cm−1), and usage of earth-abundant and non-toxic elements for the growth of thin film make it alternative to kesterite CZTSSe. In this work, we have developed CBTS thin film by a simple and cost-effective successive ionic layer adsorption and reaction (SILAR) method with a varied thickness on soda–lime glass and molybdenum-coated soda–lime glass. The optical, structural, and morphological properties were investigated, and photoresponse of the material has been characterized. Raman spectroscopy results show two vibrational peaks with a distinct peak at 341 cm−1 and also XRD showing a dominant peak for (014) plane confirming the formation of pure CBTS phase. The electrical characterization of the solution-deposited CBTS films reveals the photo-absorbing properties of the materials and predicts the promising application of these materials in the photovoltaic devices.

Morphology and structure controlled fabrication of Cu2ZnSnS4 thin films by convective assembly deposition

Thin films of Cu2ZnSnS4 (CZTS) were prepared from colloidal solution and deposited by convective assembly deposition technique. This technique is capable to control the organization of thin layer on a substrate as a result of the evaporation-driven flow or the viscous-driven flow of colloids towards the edge of meniscus when the solution is dragged across the substrate. Then, capillary-driven forces bring particles into contact with each other and the substrate. In this approach, a variety of morphologies and structures of CZTS thin films could be obtained depending mainly on the controlled deposition conditions. This work aimed to incorporate the simple yet efficient technique with detailed investigation of effects of operating parameters, including velocity of the substrate (500–1250 µm/s), annealing temperature (340–550 °C) and substrate type (glass slide and molybdenum-coated soda lime glass, Mo-coated SLG), on the properties of resulting CZTS thin films. Different morphologies of CZTS films were derived due to the effect of velocity. Furthermore, higher velocity resulted in thicker films, implying that the mechanism of convective flow in the meniscus of colloidal solution and the subsequent film formation was predominantly driven by the viscous drag. Annealing temperature strongly influenced grain growth, composition variation and enhancement of crystallinity. A unique porous structure of CZTS thin film could be obtained by deposition at a controlled velocity using Mo-coated SLG as a substrate. The key advantage of this work is the control of morphology and structure of CZTS films for various desired applications including solar cells and photoelectrochemical devices.

Strategic improvement of Cu2SnS3 thin film by different heating rates and photoluminescence investigation

Cu2SnS3 (CTS) thin films have been synthesized on molybdenum-coated soda lime glass substrates by sulfurization the Cu-Sn alloy precursors grown by radio-frequency magnetron sputtering technique. Strategic improvement has been carried out on the composition, structural, morphological and optical properties of CTS thin films sulfurized by rapid heating rate and slow heating rate. The annealing heating rate can adjust the ratio of Cu/Sn, improve the crystallinity and surface morphology. The ratio of Cu/Sn is close to the stoichiometric composition of CTS under slow heating rate with more loss of Sn. Structural characterization exhibits the CTS thin film sulfurized by slow heating rate has a better crystallinity without secondary phase. The CTS thin film obtained at slow heating rate presents a larger average grain size and smooth surface. The optical band gap of CTS thin films is at the vicinity of 0.87 eV. Photoluminescence (PL) spectroscopy has been used to study the carrier recombination mechanism and the electronic structure of CTS thin film by excitation power and temperature dependent measurements. The peak observed from PL spectra of CTS thin film conforms to the donor-acceptor pair recombination luminescence.

Optimization of ink-jet printed precursors for Cu2ZnSn(S,Se)4 solar cells

Cu2ZnSn(S,Se)4 (CZT(S,Se)) solution-based solar cells are currently drawing the attention of the photovoltaic (PV) community due to their promising efficiencies and the low-cost strategies. Although the best results were achieved by using spin coating, techniques with better controlled deposition and significantly lower material waste, such as inkjet printing, can enhance the solution-based potential. Furthermore, inkjet printing also includes the capability to write specific patterns without the use of masks or scribing tools for series interconnection of modules. In this work, a precursor ink composed by metallic salts in DMSO was optimized in terms of salts concentration and physical properties for the deposition of CZTS films onto molybdenum coated soda lime glass substrates by means of inkjet printing. In order to synthesize the solid precursor, the CZTS solution was deposited layer by layer to obtain different thicknesses using printing cycles with drying step in between. The drying temperature was also varied to evaluate the precursor morphology and its impact on the photovoltaic response of the films. Likewise, the effect of the number of cycles was also evaluated. Finally, CZTSSe solar cells were fabricated with a maximum efficiency of 6.55% without metal grid and anti-reflection layer, demonstrating the high potential of the strategy of this work.

Growth behavior of co-electrodeposited CZTS precursor thin films from acidic baths containing tartaric acid

We synthesized Cu2ZnSnS4 precursor thin films on Molybdenum-coated soda lime glass substrates using a single-step co-electrodeposition process. The as-deposited films, however, were severely Zn-poor, Sn-rich and S-poor, possessing rough, powdery surface morphologies. In this study, the effects of deposition potential, deposition time, and bath composition on the stoichiometries and morphologies of the as-deposited films are systematically investigated, with the aims to understand the growth behavior and to improve the film properties. The poor morphologies of the initial films are attributed to diffusion-limited growth modes and hydrogen co-evolution. Removal of the tartaric acid from the bath increases the bath pH, decreases the hydrogen evolution reaction, and significantly improves the film compositions and morphologies. Possible mechanisms to describe the observed deposition behavior, morphology trends, and composition trends are discussed.

Copper-Zinc-Tin-Sulfide Thin Films via Annealing of Ultrasonic Spray Deposited Nanocrystal Coatings.

Thin polycrystalline films of the solar absorber copper-zinc-tin-sulfide (CZTS) were formed by annealing coatings deposited on molybdenum-coated soda lime glass via ultrasonic spraying of aerosol droplets from colloidal CZTS nanocrystal dispersions. Production of uniform continuous nanocrystal coatings with ultrasonic spraying requires that the evaporation time is longer than the aerosol flight time from the spray nozzle to the substrate such that the aerosol droplets still have low enough viscosity to smooth the impact craters that form on the coating surface. In this work, evaporation was slowed by adding a high boiling point cosolvent, cyclohexanone, to toluene as the dispersing liquid. We analyzed, quantitatively, the effects of the solvent composition on the aerosol and coating drying dynamics using an aerosol evaporation model. Annealing coatings in sulfur vapor converts them into polycrystalline films with micrometer size grains, but the grains form continuous films only when Na is present during annealing to enhance grain growth. Continuous films are easier to form when the average nanocrystal size is 15 nm: using larger nanocrystals (e.g., 20 nm) sacrifices film continuity.

One Step Cu-Zn-Sn Alloy Deposition As a Precursor for CZTS Absorber in Photovoltaics

In recent years, research on thin film photovoltaic cells is focusing on the development of inexpensive, earth abundant and environmentally benign materials [1]. CZT(S,Se) (Cu2ZnSn(S,Se)4) thin films meet this unlike the present commercial photovoltaic thin films CIG(S,Se) (Cu(In,Ga)(S,Se)2) and CdTe. The crystal structure of CZT(S,Se) is obtained by replacing half of the indium and/or gallium in CIG(S,Se) by zinc and the other half by tin, which are both more earth-abundant materials than indium and gallium [2]. CZT(S,Se) has direct band gap of 1.0 eV (Cu2ZnSnSe4) to 1.5 eV (Cu2ZnSnS4) and a large absorption coefficient of over 104 cm-1. Up to now, many different techniques have been implemented to obtain CZTS thin films, featuring evaporation, sputtering, sol-gel deposition pulsed laser deposition, spray pyrolysis and many others. In order to reduce production costs and deployment of thin film PV-based technologies in mass scale, kesterite-based thin film solar cells technologies should be manufacturable at high throughput with low cost and it should exhibit good power conversion efficiency. Fabrication of kesterites on flexible substrate has high potential to decrease production cost due to roll-to-roll manufacturing on flexible substrate enables use of compact size deposition equipment with high throughput [3]. Recently electrodeposition has proven its utility as a solid route to obtain the CZT precursor both by plating a homogeneous Cu-Zn-Sn alloy or by subsequently depositing a stacked version of the layer; in both cases, reactive annealing is a mandatory step to introduce sulphur in the system, yielding kesterite crystals. In 2010, a one-step electrodeposition of copper-zinc-tin-sulphur precursors was described for the first time from a citrate/tartrate-based solution followed by an annealing step [4]. Although a one-step electrodeposition of the four elements would be ideal, the stoichiometric deposition of the quaternary coating is difficult to control and an additional annealing step to obtain the right ratio of the chalcogenide and to improve the crystallinity is still required. Furthermore, most researchers use thiosulfate as the sulphur source in acidic citrate/tartrate-based electrolytes, which is unstable and precipitates as sulphur. High working efficiencies have been obtained by using molybdenum coated soda lime glass as the back contact; as already said, the idea of implementing this technology at a larger production scale well suits the needing of flexible materials and low cost production techniques. In order to reduce production costs and deployment of thin film PV-based technologies in mass scale, Kesterite-based thin film solar cells technologies should be manufacturable at high throughput with low cost and it should exhibit good power conversion efficiency. Fabrication of Kesterites on flexible substrate has high potential to decrease production cost due to roll-to-roll manufacturing on flexible substrate enables use of compact size deposition equipment with high throughput. Many researchers report CZT precursor production starting from acidic baths; on the other side, even if alkaline baths for the many cited precursor deposition are known since a long time, the stability issues to which they are related make them less studied. Here we propose an alkaline electrolyte for one step deposition of the CZT precursor onto flexible molybdenum substrates. Electrochemical analyses are reported to describe the behaviour of the plating bath, as well as morphological inspection to assess the quality of the so obtained thin films. To test active layer activity, thermal annealing and reactive annealing were performed on the metallised molybdenum foil, as well as the sealing with conductive oxides via RF sputtering. After the evaporation of aluminium contacts, the efficiency of the cell was tested, yielding 0.1%. Quantum efficiency of the so obtained substrate is also reported to complete the photoactivity characterization. [1] K. Ito and T.Nakazawa, Electrical and optical properties of stannite-type quaternary semiconductor thin films, Jpn. J. Appl. Phys., 27 (1988) 2094 - 2097. [2] W. Wang, M.T. Winkler, O.Gunawan, T. Gokmen, T. K. Todorov, Y. Zhu and D.B. Mitzi, device characteristics of CZTSSe thin-film solar cells with 12.6% efficiency, Adv. Energy Mater., 4 (2014) 1301465. [3]. P. Reinhard, A. Chirila, P. Blosch, F. Pianezzi, S. Nishiwaki, S. Buecheler, A.N. Tiwari Review of progress toward 20% efficiency flexible CIGS solar cells and manufacturing issues of solar modules, IEEE J. Photovoltaics, 3 (2013) 572 - 580. [4] S.M. Pawar, B.S. Pawar, A.V. Moholkar, D.S. Choi, J.H. Yun, J.H. Moon, S.S. Kolekar, J.H. Kim, Single step electrosynthesis of Cu2ZnSnS4 (CZTS) thin films for solar cell application, Electrochim. Acta 55 (2010) 4057.

Photoelectrochemical CO2 reduction By Using Different Buffer Layers (In2S3, CdS) -Decorated Cu2ZnSnS4

Introduction Since atmospheric CO2 levels have been on the rise, global warming has become a serious problem. Recently, photoelectrochemical (PEC) CO2 reduction has attracted considerable attention as a potential means of converting solar energy into chemical energy in the form of usable organic fuels such as carbon monoxide, hydrocarbon, alcohol, and so on. To achieve the PEC CO2 reduction, the development of photocathode which possess a high energy-conversion efficiency and a high chemical stability, are strongly demanded. Cu2ZnSnS4 (CZTS) has attracted much attention as a thin film photocathode due to their specific characteristics: p-type semiconductor, high stability, ability to promote H2 evolution in response to visible light irradiation. In the present study, we fabricated CZTS photocathode by sol-gel method, and evaluated its PEC CO2 reduction properties under visible light irradiation. Moreover, we introduce n-type semiconductors (CdS, In2S3, etc.) as suitable buffer layer of the CZTS photocathode to improve the photocurrent response and selectivity of CO2 reduction. Experimental The CZTS photocathode was fabricated by sol-gel/spin-coated method on a molybdenum coated soda-lime glass (Mo/SLG) substrate. The precursor sol was prepared by dissolving raw materials (Cu2(CH3COO)2, SnCl2, Zn(CH3COO)2 and CH4N2S) into 2-methoxyethanol. Moreover, monoethanolamine was added into the prepared solution to avoid cracks during spin coating, resulting that the precursor sol was obtained. The precursor sol was spin coated on Mo/SLG substrate and annealed at 200 ℃ for 5 min on a hotplate. After this process had been repeated for a maximum of 5 times, the electrode was calcined in sulfur/N2 atmosphere. Then the CZTS photocathode was obtained. Surface modification of the CZTS photocathode was performed by chemical bath deposition (CBD) method. The CZTS photocathode was soaked in the bath solution containing raw materials for producing n-type semiconductors, and then annealed in air. Then surface modified CZTS photocathode could be prepared. The crystalline phase of CZTS was characterized by using a powder X−ray diffraction (XRD) instrument, and Raman spectroscopy. The PEC properties of the CZTS photocathode was investigated in a closed three-electrode configuration using a Ag/AgCl reference electrode and a Pt coil counter electrode. The electrolyte was 0.1 M NaHCO3 solution. The electrolyte was stirred and purged with CO2 gas for 40 min before measurement. The PEC CO2 reduction was investigated by using Xe lamp (420 < λ < 800 nm, 100 mW cm-2). The CO2 reduction products were evaluated by using gas-chromatography and ion chromatography. Results and Discussion The XRD pattern of the CZTS photocathode on Mo/SLG substrate composed of three peaks located at 28.1ﾟ, 47.0ﾟ, and 55.8ﾟ,which corresponds to (112), (220), (312) phase of kesterite structure of CZTS. For the raman spectrum, main sharp peak was observed at 336 cm-1 which ascribed to the kesterite structure of CZTS. These results indicated that the CZTS thin film could be prepared by sol-gel/spin-coating method. The morphology of CZTS thin film and surface-modified CZTS thin films were investigated by cross sectional SEM: flat and uniform films were observed. UV-vis spectrum has an absorption edge at around 830 nm, which corresponding to the optical absorption edge of the CZTS. The photocurrent of CZTS photocathode was dramatically enhanced by surface modification of n-type semiconductor layers due to efficient separation of the charge carriers at n-type/CZTS semiconductor interface (p-n heterojunction). The highest photocurrent was obtained from CdS/CZTS electrode because conduction band offset between CZTS and CdS was smaller than the other n-type layers. As a result of CO2 reduction product analysis, CO and HCOOH were obtained. Moreover, selectivity for CO2 reduction was improved by surface modification of CZTS photocathode: when CdS was deposited on the CZTS, the CO generation was increased. On the other hands, In2S3 was deposited, the HCOOH generation was increased. The detailed information will be discussed in poster session.

Intense pulsed light annealing of copper zinc tin sulfide nanocrystal coatings

A promising method for forming the absorber layer in copper zinc tin sulfide [Cu2ZnSnS4 (CZTS)] thin film solar cells is thermal annealing of coatings cast from dispersions of CZTS nanocrystals. Intense pulsed light (IPL) annealing utilizing xenon flash lamps is a potential high-throughput, low-cost, roll-to-roll manufacturing compatible alternative to thermal annealing in conventional furnaces. The authors studied the effects of flash energy density (3.9–11.6 J/cm2) and number of flashes (1–400) during IPL annealing on the microstructure of CZTS nanocrystal coatings cast on molybdenum-coated soda lime glass substrates (Mo-coated SLG). The annealed coatings exhibited cracks with two distinct linear crack densities, 0.01 and 0.2 μm−1, depending on the flash intensity and total number of flashes. Low density cracking (0.01 μm−1, ∼1 crack per 100 μm) is caused by decomposition of CZTS at the Mo-coating interface. Vapor decomposition products at the interface cause blisters as they escape the coating. Residual decomposition products within the blisters were imaged using confocal Raman spectroscopy. In support of this hypothesis, replacing the Mo-coated SLG substrate with quartz eliminated blistering and low-density cracking. High density cracking is caused by rapid thermal expansion and contraction of the coating constricted on the substrate as it is heated and cooled during IPL annealing. Finite element modeling showed that CZTS coatings on low thermal diffusivity materials (i.e., SLG) underwent significant differential heating with respect to the substrate with rapid rises and falls of the coating temperature as the flash is turned on and off, possibly causing a build-up of tensile stress within the coating prompting cracking. Use of a high thermal diffusivity substrate, such as a molybdenum foil (Mo foil), reduces this differential heating and eliminates the high-density cracking. IPL annealing in presence of sulfur vapor prevented both low- and high-density cracking as well as blistering. However, grain growth was limited even after annealing with 400 flashes. This lack of grain growth is attributed to a difficulty of maintaining high sulfur vapor pressure and absence of alkali metal impurities when Mo foil substrates are used.

Iron pyrite thin films grown through a one-step annealing of iron oxide using sulfur sources, tert-butyl disulfide and H2S

In this work, we report synthesis of pyrite thin films using tert-butyl disulfide (TBDS) and hydrogen sulfide (H2S) in one-step atmospheric pressure sulfurization of iron oxide films at 400°C on a soda-lime glass, molybdenum coated soda-lime glass and sodium-free glass substrates. The iron pyrite thin films grown using TBDS did not require the presence of sodium to form the pyrite phase, whereas H2S grown pyrite thin films did. It was observed that the pyrite formation and thus the sulfur diffusion into the oxide film was slower in TBDS compared to H2S. The synthesized films were characterized for their surface morphology and phase identification using scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The S:Fe atomic ratio as well as their chemical bonding states were monitored to obtain and maintain a stoichiometric 2:1 ratio through the entire film thickness as a function of the sulfurization time by performing an XPS depth profile. Transmittance measurements confirmed the pyrite phase with an optical bandgap of 1.15eV. The TEM electron-beam diffraction spots were used to verify the impurity phases observed in XRD patterns. Hall Effect measurements showed p-type carriers for the pyrite films.

Investigation of the electrochemical growth of a Cu–Zn–Sn film on a molybdenum substrate using a citrate solution

Cu–Zn–Sn (CZT) metallic films were electrodeposited on molybdenum-coated soda lime glass (Mo/SLG) substrates at a constant potential using an aqueous electrolyte solution containing Cu (II), Zn (II), Sn (II) ions, and tri-sodium citrate. The electrochemical growth process of the CZT film has been elucidated by analysis of the film thickness, charge consumption, elemental and phase composition, and surface morphology. Interestingly, it was found that only copper and tin were deposited in the initial stage (30 s) of electrodeposition, and after this zinc began to be incorporated into the film. Further study revealed that H2 evolution was responsible for the failed deposition of zinc on the Mo substrate. The grain size of the CZT film increased over the deposition time. It was also found that the film thickness (except for the first 1 min) increased linearly with the charge consumption, and the film grew at a constant rate. As a result, the composition of the CZT film remained constant throughout the deposition process and copper, tin, and zinc were distributed evenly in the film. Alloy phases of Cu6Sn5 and Cu5Zn8 were found in the CZT film and they were largely constant during the growth of the film. The new insight into the electrodeposition process of CZT films will be very useful for the production of high-quality solar active materials such as Cu2ZnSnS4 and Cu2ZnSnSe4.

Study on the preheating duration of Cu2SnS3 thin films using RF magnetron sputtering technique for photovoltaics

Cu2SnS3 (CTS) thin films are prepared by sulfurization the stacked metallic precursors deposited by raido-frequency magnetron sputtering method on molybdenum-coated soda lime glass substrates. The details of sulfurization process and the effect of preheating duration on the properties of CTS thin films have been investigated. It is found that the content of element tin strongly depend on the preheating duration. X-ray diffraction patterns identify that the CTS thin films exhibit the monoclinic structure. Raman scattering spectra make a further confirmation for the crystal structure. Fourier transform infrared reflectance spectroscopy (FTIR) is first used to study the properties of CTS thin films. The assigned active modes in Raman scattering spectra is consistent with the analysis in FTIR. Morphology analysis reveals long preheating duration would make the quality of films deteriorate. The thin film solar cell (TFSC) fabricated using the CTS absorber layer synthesized at preheating duration of 15 min shows that a power conversion efficiency up to 0.76% for a 0.19 cm2 area. The electrical characterization of CTS TFSC is first studied by electrochemical impedance spectroscopy, which implies the existence of MoSx and defects in the CTS/CdS interface.

Preparation of Cu2ZnSnSe4 solar cells by low-temperature co-evaporation and following selenization

Cu2ZnSnSe4 (CZTSe) thin films are prepared by a two-step method which involves co-evaporation of Cu, Zn, Sn, and Se on molybdenum-coated soda-lime glass at low substrate temperature and a following selenization. Solar cells with efficiencies of up to 6.5% can be achieved. The influence of the selenium deposition rates during co-evaporation and the nitrogen pressure during selenization on the properties of the CZTSe films are investigated. It is found that these two parameters can significantly affect the morphology and crystallinity of the CZTSe films. The possible reasons for the experimental results are discussed.

Ecofriendly and Nonvacuum Electrostatic Spray-Assisted Vapor Deposition of Cu(In,Ga)(S,Se)2 Thin Film Solar Cells

Chalcopyrite Cu(In,Ga)(S,Se)2 (CIGSSe) thin films have been deposited by a novel, nonvacuum, and cost-effective electrostatic spray-assisted vapor deposition (ESAVD) method. The generation of a fine aerosol of precursor solution, and their controlled deposition onto a molybdenum substrate, results in adherent, dense, and uniform Cu(In,Ga)S2 (CIGS) films. This is an essential tool to keep the interfacial area of thin film solar cells to a minimum value for efficient charge separation as it helps to achieve the desired surface smoothness uniformity for subsequent cadmium sulfide and window layer deposition. This nonvacuum aerosol based approach for making the CIGSSe film uses environmentally benign precursor solution, and it is cheaper for producing solar cells than that of the vacuum-based thin film solar technology. An optimized CIGSSe thin film solar cell with a device configuration of molybdenum-coated soda-lime glass substrate/CIGSSe/CdS/i-ZnO/AZO shows the photovoltaic (j-V) characteristics of Voc=0.518 V, jsc=28.79 mA cm(-2), fill factor=64.02%, and a promising power conversion efficiency of η=9.55% under simulated AM 1.5 100 mW cm(-2) illuminations, without the use of an antireflection layer. This demonstrates the potential of ESAVD deposition as a promising alternative approach for making thin film CIGSSe solar cells at a lower cost.

Fabrication of 3.01% power conversion efficient high-quality CZTS thin film solar cells by a green and simple sol–gel technique

Fine quality Cu2ZnSnS4 (CZTS) thin films were prepared by a non-toxic, simple and economical sol–gel and spin-coating technique. The CZTS thin films were prepared on Molybdenum coated soda lime glass substrates. The films were annealed at three different temperatures viz. 525, 550 and 575°C under H2S gas atmosphere to study the effect of annealing temperature on the morphological, structural, chemical, compositional, optical and photovoltaic properties of the CZTS thin films. The X-ray diffraction and Raman spectroscopy investigations on the CZTS thin films showed formation of the pure kesterite structure. The X-ray fluorescence studies demonstrated that all the CZTS thin films were nearly stoichiometric having Zn rich composition. All the annealed films were further subjected to fabrication of solar cells as an SLG/Mo/CZTS/CdS/i-ZnO/AZO/Al grid. The best solar cell showed a short-circuit current density of 14.57mA/cm2, open-circuit voltage of 513mV, fill factor of 40% and power conversion efficiency of 3.01% under air mass 1.5 (100mW/cm2) illumination.

Dynamics of the phase formation process upon the low temperature selenization of Cu/In-multilayer stacks

Phase reactions occurring during a low temperature selenization of thin In/Cu-multilayer stacks were investigated by ex-situ x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS). Therefore, dc-sputtered In/Cu-multilayers onto molybdenum coated soda lime glass were selenized in a high vacuum system at temperatures between 260 and 340 °C with different dwell times and selenium supply. The combination of the results of the phase analysis by XRD and the measurements of the in-depth elemental distribution by EDS allowed a conclusion on the occurring reactions within the layer depth. We found two CuInSe2 formation processes depending on the applied temperature. Already, at a heater temperature of 260 °C, the CuInSe2 formation can occur by the reaction of Cu2−xSe with In4Se3 and Se. At 340 °C, CuInSe2 is formed by the reaction of Cu2−xSe with InSe and Se. Because both reactions need additional selenium, the selenium supply during the selenization can shift the reaction equilibria either to the metal binaries side or to the CuInSe2 side. Interestingly, a lower selenium supply shifts the equilibrium to the CuInSe2 side, because the amount of selenium incorporated into the metallic layer is higher for a lower selenium supply. Most likely, a larger number of grain boundaries are the reason for the stronger selenium incorporation. The results of the phase formation studies were used to design a two stage selenization process to get a defined structure of an indium selenide- and a copper selenide-layer at low temperatures as the origin for a controlled interdiffusion to form the CuInSe2-absorber-layer at higher temperatures. The approach delivers a CuInSe2 absorber which reach total area efficiencies of 11.8% (13.0% active area) in a CuInSe2-thin-film solar cell. A finished formation of CuInSe2 at low temperature was not observed in our experiments but is probably possible for longer dwell times.

Fabrication of single-crystal/phase Cu2ZnSnS4 nanorods via a two-step spin coating route

In this study, we develop a two-step spin coating route without a template and use it to fabricate Cu2ZnSnS4 nanorods. Cu2ZnSnS4 nanorods with a diameter of about 30 nm were nearly perpendicular to the molybdenum-coated soda lime glass substrate. The results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy confirm that the as-synthesized products are single-crystal/phase Cu2ZnSnS4 nanorods. The effects of various factors on the formation of Cu2ZnSnS4 nanorods are also investigated. Hall effect measurement reveals that the Cu2ZnSnS4 nanorod film has p-type conductivity.

Defect chemistry and chalcogen diffusion in thin-film Cu2ZnSnSe4 materials

Selenium diffusion in polycrystalline thin-film Cu2ZnSn(S,Se)4 (CZTSe) on molybdenum-coated soda-lime glass substrates was investigated by in situ monitoring of the molybdenum back-contact resistance during high-temperature selenization treatments. In these measurements, selenium diffusion through the CZTSe layer results in conversion of the molybdenum layer to MoSe2, increasing the sheet resistance of the film stack. By monitoring the rate of MoSe2 formation as a function of annealing temperature, an activation energy of 0.5 ± 0.1 eV has been measured for selenium diffusion in CZTSe. The partial pressure dependence of chalcogen diffusion suggests that chalcogen vacancies are not the defect controlling chalcogen diffusion in thin-film CZTSe.

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.

Annealing effect for SnS thin films prepared by high-vacuum evaporation

Thin films of SnS are deposited onto molybdenum-coated soda lime glass substrates using the high-vacuum evaporation technique at a substrate temperature of 300 °C. The as-deposited SnS layers are then annealed in three different media: (1) H2S, (2) argon, and (3) vacuum, for different periods and temperatures to study the changes in the microstructural properties of the layers and to prepare single-phase SnS photoabsorber films. It is found that annealing the layers in H2S at 400 °C changes the stoichiometry of the as-deposited SnS films and leads to the formation of a dominant SnS2 phase. Annealing in an argon atmosphere for 1 h, however, causes no deviations in the composition of the SnS films, though the surface morphology of the annealed SnS layers changes significantly as a result of a 2 h annealing process. The crystalline structure, surface morphology, and photosensitivity of the as-deposited SnS films improves significantly as the result of annealing in vacuum, and the vacuum-annealed films are found to exhibit promising properties for fabricating complete solar cells based on these single-phase SnS photoabsorber layers.