CZTS Films Research Articles

Low cost copper zinc tin sulphide (CZTS) solar cells fabricated by sulphurizing sol-gel deposited precursor using 1,2-ethanedithiol (EDT)

In this paper, we report the preparation of crystalline CZTS thin films by sol–gel method followed by sulphurization using 1,2- Ethanedithiol (EDT) at 400 °C in a three zone horizontal tubular reactor equipped with computer controlled vacuum system. These films were characterized by XRD, Raman, Hall measurements and UV–Vis-NIR spectroscopy. XRD and Raman studies confirmed highly crystalline and single phase CZTS. Hall study revealed p-type semiconducting CZTS film having charge carriers density of 1.70 × 1018 cm−3 and the resistivity (ρ) of the order of 5.00 × 10−1Ω-cm. It was found that the direct band gap of 1.44 eV for CZTS film was seen from optical study. Further, double metal oxide layers having slightly different band gap were used to form a p-n junction with CZTS film. Cadmium-free solar cells with structure ITO/ZnO/CZTS/Ag (cell-1) and ITO/ZnO/com-TiO2/CZTS/Ag (cell-2) were fabricated. Electrochemical Impedance Spectroscopy (EIS) measurements were performed in the low frequency range with applied bias of 0.1 Volt for the devices. The EIS studies showed that the solar cell with ultrathin compact TiO2 layer provide a favorable path for the efficient charge transport process at the interface. The external quantum efficiency measured at 520 nm was found to be 62.5%. Cell-2 exhibited improved photovoltaic parameters with short circuit current density (Jsc) of 4.721 mA/cm2, fill factor of 0.46 and open circuit voltage (Voc) of 400 mV. The short circuit current density and fill factor of double metal oxide layers (cell-2) were increased by 78% and 46%, respectively, as compared to single metal oxide layer (cell-1).

Growth of Cu2ZnSnS4 thin films by hybrid chemical approach

Thin films of Cu2ZnSnS4 (CZTS), an emerging solar cell absorber layer, were prepared by a hybrid chemical process followed by annealing. In this process, two binary layers, SnS and ZnS were grown sequentially using chemical bath deposition method (CBD) onto soda-lime glass substrates. Subsequently the ZnS layer was partly converted into CuxS layer through an ion-exchange process by immersing the stack glass/SnS/ZnS in CuCl2 solution. The resulting stack, namely glass/SnS/ZnS/CuS, was annealed in sulphur atmosphere at 450 °C for an hour to promote inter-diffusion of the layers leading to the formation of CZTS film through the solid-state reaction path. The stack with a ZnS layer of 470 nm thick and 270 nm thick SnS led finally to the desired CZTS phase formation. XRD analysis of these films showed CZTS peaks which are close to the Cu2SnS3 (CTS) phase. Raman spectra recorded to distinguish CTS and CZTS phases showed modes at 291, 338 cm−1 corresponding to CZTS phase confirming its formation. The band gap of CZTS films is found to be 1.42 eV. The films were found to be p-type in nature. An attempt is made to fabricate heterojunction solar cell.

Effect of sulfurization temperature on Cu-Zn disorder for non-stoichiometric spray pyrolyzed Cu2ZnSnS4 thin films

Cu2ZnSnS4(CZTS) thin-films were synthesized using chemical spray pyrolysis technique followed by sulfurization at different temperatures via the chemical vapor deposition technique. The Cu-Zn disorder for the films sulfurized at various temperatures was investigated using the near-resonance Raman spectra with an excitation wavelength of 785 nm. The sulfurized films exhibited optimal non-stoichiometric Cu-poor and Zn- rich composition to achieve higher solar cell efficiency. The CZTS films sulfurized at a temperature of 550 °C exhibited higher Cu-Zn order.

Investigation on in-situ thermal treatment of room-temperature pulsed laser deposition technique: How to improve Cu2ZnSnS4 films for photoelectric application without sulfurization

Is extra sulfurization an indispensable process for synthesizing quaternary chalcogenide? The answer is probably affirmative for most synthesismethods to suppress excessive sulfur vacancies. Pulsed laser deposition (PLD), an acknowledged technique for fabricating films with complex stoichiometry, is a greatalternative approach to prepare Cu2ZnSnS4 (CZTS) films. However, to prevent evaporative losses the deposition temperature (Tis) must be limited below 400 °C, which makes post-annealing process extremely requisite to improve metastable films. Herein we develop an in-situ thermal treatment technique in room-temperature (RT)-PLD-synthesis of CZTS films to evade extra sulfurization process. According to multi-peaks Gaussian fitting analysis, RT-PLD implementing optimized in-situ treatment can broaden solar absorption of CZTS films, potentially contributed by sub-bandgap absorption due to intrinsic natural-intermedium-band effects of I2-II-IV-VI4 chalcogenide compounds. Stabilized chronoamperometry characterization combined with quasi-stoichiometric ratio demonstrates that the RT-PLD technique can equivalently restrain sulfur vacancy generation even without sulfurization. Physical mechanisms associated to order–disorder transitions of polycrystal CZTS during in-situ treatment can interpret morphological “lumpy-smooth-vuggy” transformation along with Tis varied. Therefore, such proposed RT-PLD technique is applicable to prepare polynary compounds with volatile elements and complicated stoichiometry ratio.

Effect of sodium-doping on the performance of CZTS absorb layer: Single and bifacial sodium-incorporation method

In current work, sodium doped CZTS films are deposited onto Mo-coated stainless-steel foil for fabrication of flexible solar cells. New strategies for sodium incorporation of Cu2ZnSnS4 (CZTS) thin films are introduced and investigated. In detail, bilayer NaF film was deposited at the bottom and on the top of CZTS films to obtain a uniformly doped CZTS film. For comparison, CZTS films were also doped with a single layer NaF from bottom and top, respectively. Secondary ion mass spectroscopy (SIMS) is applied to investigate the distribution of different elements along the depth, X-ray diffraction and Raman spectroscopy are used to identify the crystallinity and secondary phases. Finally, solar cells are assembled based on the prepared CZTS films with an efficiency of 2.3%. Although the obtained devices show a far lower efficiency compared with other reports, current research provides a feasible path for sodium incorporation when fabricating CZTS films on Na-free substrates.

Sol-gel prepared Cu2ZnSnS4 (CZTS) semiconductor thin films: Role of solvent removal processing temperature

The conditions under which thin films are deposited are the most important parameter determining the physical performance of devices. In this work, we present the effect of preheating temperatures under N2 ambient conditions on the quality of Cu2ZnSnS4 (CZTS) thin films. Herein we are interested in the structural, morphological, vibrational, optical and electrical characteristics of CZTS layers, synthesized using the sol-gel method. CZTS layers were deposited at preheating temperatures of 200 °C, 250 °C and 300 °C under N2 ambient atmosphere prior to a 1-h sulphuration process at 580 °C. XRD results confirm the dependence of the crystallite size on temperature. All the deposited layers are in stannite phase, confirmed by Raman spectroscopy, and the electrical properties show that all films obtained are p-type semiconductors with a carrier charge concentration of 4.06–9.48 × 1020 cm−3. CZTS films preheated at 300 °C show better crystallinity, larger grains, more suitable band gap, higher electrical conductivity and improved surface morphology compared to the rest of the thin films, which indicates that the method proposed here can be used to deposited high quality absorber layers of CZTS for solar cells applications.

Solution‐Processed Semitransparent CZTS Thin‐Film Solar Cells via Cation Substitution and Rapid Thermal Annealing

Semitransparent solar cells are able to capitalize on land scarcity in urban environments by co‐opting windows and glass structures as power generators, thereby expanding the capacity of photovoltaics to meet energy needs. To be successful, devices must be efficient, possess good visual transparency, long‐term stability, and low cost. Copper zinc tin sulfide is a promising thin‐film material that consists of earth‐abundant elements. For optical transparency, the usual molybdenum back contact is replaced with a transparent conducting oxide (TCO). However, due to subsequent high‐temperature annealing, the TCO degrades, losing conductivity, or forms a poor interface with CZTS. Lower temperatures mitigate this issue but hinder grain growth in CZTS films. Herein, cadmium substitution and silver and sodium doping are used to aid grain growth and improve film quality at lower annealing temperatures. Thin molybdenum is sputtered on TCO to help improve the interface transition postannealing by conversion to MoS2. Rapid thermal processing is used to minimize high‐temperature exposure time to preserve the TCO. With these methods, a semitransparent device with a front illumination efficiency of 2.96% is demonstrated.

One-step CZT electroplating from alkaline solution on flexible Mo foil for CZTS absorber

In this work, Cu-Zn-Sn (CZT) is co-electrodeposited onto a flexible Mo substrate exploiting an alkaline bath (pH 10). The plating solution is studied by cyclic voltammetry, highlighting the effects of potassium pyrophosphate (K4P2O7) and EDTA-Na2 on the electrochemical behavior and stability of the metallic ionic species. The optimized synthesis results in a homogeneous precursor layer, with composition Cu 44 ± 2 at. %, Zn 28 ± 1 at. %, and Sn 28 ± 2 at. %. Soft and reactive annealing are employed respectively to promote intermetallic phase formation and sulfurization of the precursor to obtain CZTS. Microstructural (XRD, Raman), morphological (SEM), and compositional (EDX, XRF) characterization is carried out on CZT and CZTS films, showing a minor presence of secondary phases. Finally, photo-assisted water splitting tests are performed considering a CZTS/CdS/Pt photoelectrode, showing a photocurrent density of 1.01 mA cm−2 at 0 V vs. RHE under 1 sun illumination.Graphical abstract

Enhancing the performance of Cu2ZnSnS4 solar cell fabricated via successive ionic layer adsorption and reaction method by optimizing the annealing process

Kesterite Cu2ZnSnS4 (CZTS) solar cells are regarded as a promising photovoltaic technology owing to the non-toxic and earth-abundant constitutes. With the application of scalable and low-cost solution methods, the possibility of its commercialization can be further increased. This work explores preparing prominent CZTS films by an economically feasible successive ionic adsorption and reaction (SILAR) synthesis method. The obtained precursor with the Mo/ZnS/Cu2SnS3 structure requires appropriate substantial annealing under a chalcogen atmosphere to form kesterite CZTS films. The annealing process is therefore optimized to improve the film quality and the performance of solar cells. Specifically, the optimal annealing condition is determined by adjusting the annealing temperature and holding time, respectively. The CZTS film annealed at 580 °C for 60 min demonstrates better film quality in terms of surface morphology, crystallinity, and phase purity. Consequently, CZTS solar cells fabricated with the optimal absorber exhibit a preferable efficiency of up to 4.26%.

Effect of volume of the solution and sulfurization on properties of Cu2ZnSnS4 thin films fabricated by spray assisted chemical vapour deposition method

ABSTRACT Cu2ZnSnS4 thin films were produced by spray assisted chemical vapor deposition process (SACVD) technique using different volumes of aqueous ionic solution, followed by sulfurization in sulfur vapors at 500°C and under Argon atmosphere. These CZTS thin films were analysed by X-ray diffraction and Raman scattering analysis that have confirmed the kesterite phase structure of CZTS films before and after sulfurization. The optimum band gap of the as-deposited CZTS films are between 1.40 and 1.43 eV. The cristallinity of the layers improve after sulfurization and their band gap varies between 1.44 and 1.50 eV. The surface morphology of the samples was examined by scanning electron microscopy. The chemical composition was determined by energy dispersive X-ray spectroscopy which shows the formation of Cu poor and Zn rich sulfurized CZTS thin films. Hall Effect measurements revealed that all the films before and after sulfurization are p-type. The sulfurized films obtained in our laboratory have carrier concentrations ranging from 3.1 to 6.8 x 1018 cm-3, a resistivity between 0.199 and 0.262 Ω.cm and mobility between 3.5 and 10.1 cm2/V.s.

Effect of thiourea on structure, morphology and optical properties of spray deposited CZTS thin films for solar cell applications

<p>Cu2ZnSnS4 (CZTS) films of different Thiorea (SC (NH2)2) molarity were deposited by using simple chemical spray technique at substrate temperature 275°C. Analytical reagent Grade Copper chloride (CuCl2), Zinc chloride (ZnCl2), Tin chloride (SnCl4.5H2O) were used as Cu+ , Zn+ , and Sn+ ion sources respectively and thiourea (SC(NH2)2) (0.02, 0.04 0.06 0.08, and 0.1 M) was used as a Sion source. A set of five CZTS films was deposited using five different molarity of thiourea. The structure, Morphology, Elemental analysis and optical properties of these films were studied using X-ray diffratometer (XRD), Scanning Electron Microscopy (SEM) Energy Dispersive X-ray Analysis (EDX) and UV-Visible spectroscopy techniques respectively. The XRD spectra showed that all films are polycrystalline tetragonal structure with preferential orientation along (112) plane. The calculated crystallite size was increased with increase in thiourea concentration. Variations of optical band gap with thiourea molarity have been investigated using Tauc plots. SEM micrographs exhibits CZTS spherical granules regularly arranged with some void spaces. Purity of deposited films was investigated using EDX analysis. All the CZTS films exhibits higher absorption coefficient (𝛼 > 104) cm-1 and band gap in the reported range (1.2-1.53 eV) can be used as an absorber layer in solar cells.</p>

Na incorporation into Cu2ZnSnS4 thin film absorbers from RF-sputtered NaF precursors

In this work, we report the incorporation of sodium (Na) alkaline element into copper-zinc-tin-sulphide (Cu-Zn-Sn-S) precursor films by adding radio frequency (RF)-sputtered sodium fluoride (NaF) intermediate layers bringing a new approach to the bifacial sodium-incorporated treatment (BIST) and its effect on the properties of Cu2ZnSnS4 (CZTS) absorber films. Due to the absence of alkaline diffusion barrier layers on soda lime glass (SLG) substrates, Na additions from both NaF intermediate layers and SLG substrate were evaluated together. With additional NaF intermediate layers among the elemental metal stacks, the films exhibited better crystalline properties and a more compact structure. However, the amount of the Cu2-xS secondary phases formed on the surfaces increased by the additional NaF layers. Raman spectra confirmed the formation of the kesterite phase and showed the peaks corresponding to Cu3SnS4 and Cu2-xS secondary phases. Na diffusion originating from NaF layers deposited on molybdenum (Mo) films occurred in both directions of the CZTS film and the SLG substrate. The photoluminescence (PL) bands located at around 1.40 eV were attributed to the band to band (BB) transitions. The film with additional NaF intermediate layers exhibited higher carrier concentrations and lower resistivity than the other film due to the presence of the higher amount of Cu2-xS secondary phases on its surface.

High-efficiency ultra-thin Cu2ZnSnS4 solar cells by double-pressure sputtering with spark plasma sintered quaternary target

In recent years, Cu2ZnSnS4 (CZTS) semiconductor materials have received intensive attention in the field of thin-film solar cells owing to its non-toxic and low-cost elements. In this work, double-pressure sputtering technology is applied to obtain highly efficient and ultra-thin (~450 nm) pure Cu2ZnSnS4 (CZTS) solar cell. Using mixed materials with sulfides and copper powder as a quaternary target via spark plasma sintering (SPS) method and adopting double-layer sputtering (high + low pressure), a highly adhesive and large-grained CZTS thin film is achieved. As a result, the damage to the surface of Mo contact is decreased so that the reflectivity of incident light can be improved. Moreover, the composition of CZTS film was more uniform and the secondary phase separation at the Mo interface was reduced. Therefore, the interface defect state and deep level defect density in corresponding device with double-pressure is reduced and the ratio of depletion thickness to absorption layer thickness can reached to 0.58, which promoted the collection of photogenerated carriers. Finally, an efficiency of 9.3% for ultra-thin (~450 nm) CZTS film solar cell is obtained.

Copper concentration effect on physical properties of ultrasonically sprayed Cu2ZnSnS4 absorber thin films for solar cell applications

Cu2ZnSnS4 (CZTS) thin films have been successfully deposited on glass substrate using ultrasonic spray pyrolysis (USP) technique with different copper concentrations ranging from 0.005 to 0.020 M. The effect of copper concentration on the structural, morphological and optoelectrical properties of deposited films has been investigated. Choice of USP method and copper concentration was found to have a crucial role in stoichiometry, band gap and conductivity of sprayed CZTS thin films. X-ray diffraction indicated that all deposited films have CZTS Kesterite structure with a preferential orientation along (112) plane confirmed by Raman scattering measurements. Copper sulfide (CuS) is present as a secondary phase in all films. The presence of this secondary phase causes films optical band broadening. Good film with nearly stoichiometric CZTS film and desirable band gap of 1.51 eV was obtained at copper concentration of 0.015 M. This result indicates that this film is suitable for being applied as an absorber layer in photovoltaic solar cells.

Influence of thiourea in the precursor solution on the structural, optical and electrical properties of CZTS thin films deposited via spray coating technique

CZTS films were prepared by spray coating using non-aqueous precursor solutions with and without sulphur source and studied their structural, optical and electrical properties. The films prepared by both the routes were sulphurized at different temperatures to study the effect of temperature on the phase formation. Phase purity was confirmed by XRD, Raman analysis and Rietveld refinement technique. The studies revealed proper phase and crystallinity for the films of both routes sulphurized at 550 °C. These films exhibited dense and improved grain structure, optimal bandgap and higher absorption coefficient. The non-thiourea films sulphurized at 550 °C had a carrier concentration of 1.544 × 1019 cm−3, mobility of 0.87 cm2V−1 s−1 and resistivity of 0.46 Ω·cm, while the thiourea films achieved carrier concentration, mobility and resistivity of 3.67 × 1019 cm−3, 0.33 cm2V−1 s−1 and 0.52 Ω·cm, respectively. The comparative study demonstrates that the films under investigation have the potential for the fabrication of efficient solar cells.

Characterization of Cu2ZnSnS4 thin films deposited by one-step thermal evaporation for a third generation solar cell

In this study, one-step thermal evaporation was employed for the fabrication of phase-pure CZTS thin films on glass substrates from single crystalline Cu-poor ingot grown by Bridgman technique. Structural analyses revealed the formation of a mono-phase CZTS kesterite structure for the thin films annealed at 450 °C under N2 atmosphere. The AFM measurements demonstrated significant morphological changes in films with increasing the annealing temperature from 200 °C to 450 °C, supporting the results obtained via XRD and Raman studies. From the optical measurements, the band gap was estimated to be 1.47 eV for the CZTS film annealed at 450 °C, which is close to the optimum value required for photovoltaic applications. As a device application of the optimized CZTS thin films, an attempt was made to construct a TiO2 NRs based and CdS-free FTO/TiO2 NRs/CZTS/Ag superstrate CZTS solar cells. TiO2 NRs were grown by hydrothermal technique, which offers a simple and a cost-effective route for large-scale production of one-dimensional nanostructures. The solar cell exhibited an open-circuit voltage of 0.35 V, a short-circuit current density of 7.28 mA/cm2, a fill factor of 23.9% and a power conversion efficiency of 0.61%, the highest efficiency recorded so far for a single-dimensional TiO2 nanostructures based superstrate CZTS solar cell.

Optimization of adsorption and reaction time of SILAR deposited Cu2ZnSnS4 thin films: Structural, optical and electrochemical performance

Nano-crystalline quaternary Cu2ZnSnS4 (CZTS) thin films have been deposited over the conducting and non-conducting substrates by SILAR method with different dipping times. A variety of techniques were employed for the characterization of structural, vibrational, optical, morphological with compositions, and electrochemical properties of the annealed films. The XRD patterns confirmed the formation mingled phase of wurtzite and kesterite structures. The FTIR spectra established the metal vibrations of CZTS films. Microscopically analyses have been revealed the morphology of the annealed films as homogeneous and uniformly distribution agglomerated spherical shaped particles. The optical spectra show the maximum optical absorption in the visible region. The band gap has been calculated using Tauc’s relation and obtained bandgap is in the range of 1.46–1.82 eV. Electrochemical performance of Cu2ZnSnS4 films has been tested by cyclic voltagrams (CV), Galvanostatic charge-discharge (GCD) and Electrochemical impedance spectroscopy (EIS) analysis. Particularly current run with 1000 cycles, retentivity of the working electrode is 99.69% at Cu2ZnSnS4-52 film.

Study of the semiconducting properties of Cu2ZnSnS4 thin films grown by ultrasonic spray pyrolysis of water-dissolved precursors

Cu2ZnSnS4 (CZTS) thin films were deposited on glass-slide substrates by ultrasonic spray pyrolysis at the substrate temperatures in the 330–420 °C range, using water–ethanol solutions containing CuCl2–H2O, ZnCl2, SnCl2, and (NH2)2CS (thiourea). After being deposited, CZTS films were annealed under vacuum and then characterized in regarding their structural and optical properties. The X-ray diffraction and Raman spectroscopy studies indicated that CZTS thin films with kesterite as predominant phase could be obtained. The X-ray diffraction patterns of all deposited samples displayed diffraction peaks corresponding to the planes (112), (220), and (312) of kesterite CZTS and diffraction peaks belonging to phases other than CZTS were apparently undetectable for the X-ray technique. Furthermore, their Raman spectra were featured for a widely structured Raman band in the 200–400 cm−1 wavenumber area. After being deconvoluted, Raman peaks belonging only to kesterite CZTS were revealed. However, a further analysis of the UV–Vis absorbance spectra indicated all our films strongly absorbs in this spectral region. In the low photon energy region (< 1.5 eV), Tauc plots revealed electron transitions with characteristic energy values in the 1.15–1.34 eV range, which could be attributed at the presence of tetragonal Cu2SnS3 and point defects (VS and VZn) into CZTS. All prepared CZTS films display the p-type conductivity as verified by Hall measurements.

The investigation of the corrosion behavior of CZTS thin films prepared via electrodeposition

In this study, Cu2ZnSnS4 (CZTS) thin films were deposited on indium tin oxide (ITO)-coated glass substrate by single-step electrochemical deposition (ECD). CZTS absorber layers were obtained with −1.05 V cathodic potential and 2700 s deposition time for pH:5 and at room temperature. Trisodium citrate was used as a complexing agent for co-electrodeposition. After the deposition, the CZTS thin films were annealed at 580 °C in sulfur powder and N2 atmosphere for 60 min for the formation of stoichiometric kesterite structure. The structural, morphological and optical properties of the prepared thin films were investigated by X-ray diffraction (XRD) analysis, optical absorption techniques, scanning electron microscopy (SEM) observations and Raman spectroscopy measurements. Crystallisation of the films was confirmed by XRD measurements. The prepared films were also examined using Electrochemical Impedance Spectroscopy (EIS) and Tafel measurements. Nyquist, open circuit voltage (OCV) voltage(OCP) and Bode analysis were used to find out the structural changing and corrosion behavior of the CZTS films. The equivalent circuit parameters such as solution resistance (Rs), polarization resistance (Rp), a constant phase element (CPE), a CPE exponent (n) and diffusion potential were calculated as 253.8 Ω cm2, 944.2 Ω cm2, 1.547 × 10−3 Ω−1 s cm−2, 0.500 and 8.631 × 10−3 Ω−1 s1/2. cm−2, respectively. Also, with the help of Tafel measurements, the corrosion potential and current values were determined as −0.161 V and 1 × 10−6 A, respectively.

Studies on Cu2ZnSnS4 (CZTS) powder and thin film prepared from Molecular ink

Abstract Copper Zinc Tin Sulphide (Cu2ZnSnS4) is one of the most promising materials in the field of thin film based solar cell. Nanoparticles and ink form of CZTS prepared by chemical method is well-studied. In the present work CZTS powder made from chemical method and used to prepared films by physical evaporation technique, i.e. flash evaporation. CZTS films were prepared at 200 °C substrate temperature and annealed at 300 °C and 450 °C in vacuum for one hour. The structural, morphological, optical and electrical properties of the as-deposited and annealed were studied. The XRD confirms the wurtzite structure of the CZTS films. Atomic force microscopy indicates that the surface morphology also improves with the annealing. The band gap value of the annealed films is 1.7 eV, implied that the formation of the CZTS material. An electrical measurement signifies the p-type conductivity of the films. As a sum-up, as-deposited films were amorphous, non-uniform and highly resistive, and after annealing all had improve.