Aqueous bath process for deposition of Cu2ZnSnS4 photovoltaic absorbers

Chemical bath deposition and ion exchange were used to incorporate copper, zinc, tin and sulfur into a thin film precursor stack. The stack was then sulfurized to form the photovoltaic absorber material Cu₂ZnSnS₄ (CZTS). The morphology and elemental composition of the films at each process stage were analyzed by Auger electron spectroscopy and scanning electron microscopy, and the structural and optical properties of the sulfurized film were determined by a combination of X-ray diffraction, Raman scattering, and diffuse reflectance UV-Vis spectroscopy. Compositionally uniform microcrystalline CZTS with kesterite structure and a bandgap of 1.45 eV were observed. A preliminary solar cell device was produced exhibiting photovoltaic and rectifying behavior.     

Multi-stage evaporation of Cu2ZnSnS4 thin films

Multi-stage evaporation is a well-established method for the controlled growth of chalcopyrite thin films. To apply this technique to the deposition of Cu₂ZnSnS₄ thin films we investigated two different stage sequences: (A) using Cu₂SnS₃ as precursor to react with Zn-S and (B) using ZnS as precursor to react with Cu-Sn-S. Both Cu₂SnS₃ and ZnS are structurally related to Cu₂ZnSnS₄. In case (A) the formation of copper tin sulphide in the first stage was realized by depositing Mo/SnS_x/CuS (1 < x < 2) and subsequent annealing. In the second stage ZnS was evaporated in excess at different substrate temperatures. We assign a significant drop of ZnS incorporation at elevated temperatures to a decrease of ZnS surface adhesion, which indicates a self-limited process with solely reactive adsorption of ZnS at high temperatures. In case (B) firstly ZnS was deposited at a substrate temperature of 150 °C. In the second stage Cu, Sn and S were evaporated simultaneously at varying substrate temperatures. At temperatures above 400 °C we find a strong decrease of Sn-incorporation and also a Zn-loss in the layers. The re-evaporation of elemental Zn has to be assumed. XRD measurements after KCN-etch on the layers prepared at 380 °C show for both sample types clearly kesterite, though an additional share of ZnS and Cu₂SnS₃ can not be excluded. SEM micrographs reveal that films of sample type B are denser and have larger crystallites than for sample type A, where the porous morphology of the tin sulphide precursor is still observable. Solar cells of these absorbers reached conversion efficiencies of 1.1% and open circuit voltages of up to 500 mV.     

Single step synthesis of chalcogenide nanoparticles Cu2ZnSnS4, Cu2FeSnS4 by thermal decomposition of metal precursors

Cu₂ZnSnS₄ (CZTS) and Cu₂FeSnS₄ (CFTS) nanoparticles were synthesized by thermal decomposition of metal precursors. Dispersion of the precursors in the solvent prior to reaction significantly lowered the temperature and time required for the reaction. Extensive characterization of the synthesized nanoparticles was done. Materials characteristics of the synthesized nanoparticles such as elemental composition, band gap and morphology were found to be similar to the nanoparticles prepared by conventional synthesis techniques.     

Reactive sputtering of precursors for Cu2ZnSnS4 thin film solar cells

The quaternary semiconductor Cu₂ZnSnS₄ (CZTS) is a possible In-free replacement for Cu(In,Ga)Se₂. Here we present reactive sputtering with the possibility to obtain homogeneous CZTS-precursors with tunable composition and a stoichiometric quantity of sulfur. The precursors can be rapidly annealed to create large grained films to be used in solar cells. The reactive sputtering process is flexible, and morphology, stress and metal and sulfur contents were varied by changing the H₂S/Ar-flow ratio, pressure and substrate temperature. A process curve for the reactive sputtering from CuSn and Zn targets is presented. The Zn-target is shown to switch to compound mode earlier and faster compared to the CuSn-target. The precursors containing a stoichiometric amount of sulfur exhibit columnar grains, have a crystal structure best matching ZnS and give a broad peak, best matching CZTS, in Raman scattering. In comparing process gas flows it is shown that the sulfur content is strongly dependent on the H₂S partial pressure but the total pressures compared in this study have little effect on the precursor properties. Increasing the substrate temperature changes the film composition due to the high vapor pressures of Zn, SnS and S. High substrate temperatures also give slightly denser and increasingly oriented films. The precursors are under compressive stress, which is reduced with higher deposition temperatures.     

Synthesis and characterization of Cu2ZnSnS4 absorber layers by an electrodeposition-annealing route

An electrodeposition-annealing route to films of the promising p-type absorber material Cu₂ZnSnS₄ (CZTS) using layered metal precursors is studied. The dependence of device performance on composition is investigated, and it is shown that a considerable Cu-deficiency is desirable to produce effective material, as measured by photoelectrochemical measurements employing the Eu^3+/2+ redox couple. The differing effects of using elemental sulphur and H₂S as sulphur sources during annealing are also studied, and it is demonstrated that H₂S annealing results in films with improved crystallinity.     

Spectroscopic ellipsometry study of Cu2ZnGeSe4 and Cu2ZnSiSe4 poly-crystals

We report the room temperature spectroscopic ellipsometry study of Cu₂ZnGeSe₄ and Cu₂ZnSiSe₄ crystals, grown by modified Bridgman technique. Optical measurements were performed in the range 1.2–4.6 eV. The spectral dependence of the complex pseudodielectric functions as well as pseudo- complex refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity of Cu₂ZnGeSe₄ and Cu₂ZnSiSe₄ crystals were derived. The observed structures in the optical spectra were analyzed by Adachi's model and attributed to the band edge transitions and higher lying interband transitions. The parameters such as strength, threshold energy, and broadening, corresponding to the E₀, E_1A and E_1B interband transitions, have been determined using the simulated annealing algorithm.     

Cu2ZnSnS4-CdS复合材料的制备及其在光催化制氢中的应用

为了进一步提高Cu₂ZnSnS₄的光催化制氢性能,首先通过水热法制备出Cu₂ZnSnS₄光催化材料,在此基础上加入Cd（CH₃COO）₂·2H₂O和Na₂S进行二次水热反应制备Cu₂ZnSnS₄-CdS复合材料。通过XRD、SEM、TEM、Raman及XPS等分析测试方法对Cu₂ZnSnS₄-CdS复合材料的物相结构、微观形貌和元素价态进行了表征。结果表明:成功制备了结晶性能较好的Cu₂ZnSnS₄-CdS复合材料。Cu₂ZnSnS₄-CdS复合材料是由球状和块状颗粒组成;Cu₂ZnSnS₄-CdS复合材料表面>95%的Cd和S原子（原子比为1:1）的存在说明块状颗粒Cu₂ZnSnS₄表面生长的球形颗粒为CdS;在氙灯下的光催化制氢性能表明,Cu₂ZnSnS₄-CdS复合材料的光催化制氢效果明显优于Cu₂ZnSnS₄和CdS,产氢效率为296.17 μmol（g·h）-1。      

Cu2ZnSnS4纳米颗粒及其薄膜的制备与表征

采用热注入法,在油胺(OLA)中合成出Cu2ZnSnS4(CZTS)纳米颗粒,并在玻璃衬底上制备了薄膜,研究了不同合成温度对纳米颗粒生成的影响.通过X射线衍射仪、拉曼光谱仪、透射电子显微镜、扫描电子显微镜、紫外可见分光光度计对所得纳米晶材料的结构与成分、颗粒大小与形貌、光吸收谱进行了测试分析.研究结果表明:采用热注入法的最佳合成温度在260℃左右,该温度下生成的多晶CZTS纳米颗粒尺寸约10 nm,分散性良好,光学禁带宽度约1.5 eV.     

Cu2ZnSnS4/Si异质结器件的制备及特性研究

利用脉冲激光沉积法在不同电阻率的n型Si(100)基片上沉积Cu2ZnSnS4薄膜,制备p-Cu2ZnSnS4/n-Si异质结.利用X射线衍射(XRD)、X射线能谱(EDS)和原子力显微镜(AFM)对Cu2ZnSnS4薄膜的结构、组分和形貌进行表征,并对器件进行I-V测试,讨论不同电阻率的Si对异质结器件光电特性的影响.结果表明,器件有良好的整流特性,Si电阻率大的器件光电响应比较好,而Si电阻率小的器件光伏效应比较明显.     

New compounds Cu2MnTi3S8 and Cu2NiTi3S8 with thiospinel structure

Cu₂MnTi₃S₈ and Cu₂NiTi₃S₈ compounds were prepared by high-temperature synthesis. The crystal structure of these quaternary phases was investigated by X-ray powder diffraction. The compounds are described in the thiospinel structure (space group ) with the lattice constants a = 1.00353(1) nm (Cu₂MnTi₃S₈) and a = 0.99716(1) nm (Cu₂NiTi₃S₈). The atomic parameters were calculated in anisotropic approximation (R_I = 0.0456 and R_I = 0.0520 for Cu₂MnTi₃S₈ and Cu₂NiTi₃S₈, respectively).     

阳离子部分取代Cu2ZnSnS4的研究进展

P型半导体Cu_2ZnSnS_4(CZTS)由于具有最佳的直接带隙(1.0~1.5eV)、高的光吸收系数(超过104 cm~(-1))以及丰富、无毒的元素组成,使其成为商业化低成本太阳能电池最有希望的候选材料之一。然而,材料本身的一些缺陷制约了CZTS薄膜太阳能电池效率的提高。为了提高CZTS薄膜太阳能电池的效率,研究者们使用其他阳离子部分取代Cu、Zn或Sn来改善CZTS的缺陷。从CZTS的3种不同取代位置出发,综述了近年来各种阳离子部分取代CZTS的研究进展,同时对阳离子部分取代CZTS材料的发展前景进行了展望。     

Cu2ZnSnS4 solar cell prepared entirely by non-vacuum processes

Cu₂ZnSnS₄ (CZTS) solar cell with superstrate structure of fluorine-doped tin oxide glass/TiO₂/In₂S₃/CZTS/Carbon was prepared entirely by non-vacuum processes. The compact TiO₂ window and In₂S₃ buffer layers, CZTS absorber layer and Carbon electrode layer were prepared by spray pyrolysis method, ball milling and screen printing combination processes and screen printing process, respectively. The short-circuit current density, open-circuit voltage, fill factor and conversion efficiency of the best fabricated solar cell are 8.76 mA/cm², 250 mV, 0.27 and 0.6%, respectively. The fabrication process for the CZTS solar cell did not employ any vacuum conditions or high-toxic materials (such as CdS, H₂Se, H₂S or Se).     

Growth and Raman scattering characterization of Cu2ZnSnS4 thin films

In the present work we report the results of the growth, morphological and structural characterization of Cu₂ZnSnS₄ (CZTS) thin films prepared by sulfurization of DC magnetron sputtered Cu/Zn/Sn precursor layers. The adjustment of the thicknesses and the properties of the precursors were used to control the final composition of the films. Its properties were studied by SEM/EDS, XRD and Raman scattering. The influence of the sulfurization temperature on the morphology, composition and structure of the films has been studied. With the presented method we have been able to prepare CZTS thin films with the kesterite structure.     

Theoretical study of the gap evolution of In2X3 (X=O, S, Se, Te) with lattice compression

We report a systematic study of the electronic structure of In₂X₃ (X=O, S, Se, Te) semi-conductors using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method. Taking into account the experimental structure of each compound we have determined the gap evolution under lattice compression in the whole series. We have found that the compression of the lattice produces an enhancement of the energy gap. This could be driven in some cases by doping with shallow impurities.     

Predicted formation reactions for the solid-state syntheses of the semiconductor materials Cu2SnX3 and Cu2ZnSnX4 (X = S, Se) starting from binary chalcogenides

The compounds Cu₂ZnSnX₄ and Cu₂SnX₃ (X = S or Se) are promising semiconductor materials for thin film photovoltaic applications. Based on a crystallographic growth model we derive the solid-state reactions for these four compounds starting from the binary sulphides and selenides of copper, zinc and tin. Exploiting these predicted solid-state reactions which are promoted by epitaxial relations between the educts will result in fast formation reactions as preferred in technical processes. The direct formation of Cu₂ZnSnX₄ is concurring with a two-step process in which Cu₂SnX₃ occurs as an intermediate product.     

Study of optical and structural properties of Cu2ZnSnS4 thin films

Cu₂ZnSnS₄ is a promising semiconductor to be used as absorber in thin film solar cells. In this work, we investigated optical and structural properties of Cu₂ZnSnS₄ thin films grown by sulphurization of metallic precursors deposited on soda lime glass substrates. The crystalline phases were studied by X-ray diffraction measurements showing the presence of only the Cu₂ZnSnS₄ phase. The studied films were copper poor and zinc rich as shown by inductively coupled plasma mass spectroscopy. Scanning electron microscopy revealed a good crystallinity and compactness. An absorption coefficient varying between 3 and 4 × 10⁴cm^− 1 was measured in the energy range between 1.75 and 3.5 eV. The band gap energy was estimated in 1.51 eV. Photoluminescence spectroscopy showed an asymmetric broad band emission. The dependence of this emission on the excitation power and temperature was investigated and compared to the predictions of the donor-acceptor-type transitions and radiative recombinations in the model of potential fluctuations. Experimental evidence was found to ascribe the observed emission to radiative transitions involving tail states created by potential fluctuations.     

An evaluation of depletion layer photoactivity in Cu2ZnSnS4 thin film

Cu₂ZnSnS₄ films were examined in Eu^3 +/Eu^2 + electrolyte to evaluate various analytical expressions for photocurrent response as a function of applied potential. A Gärtner model, which considers charge transfer (across the double layer) was evaluated. This model shows an adequate fit in the negative photocurrent region. The fit of the Gärtner model over a broader range of photocurrent is improved by modifying it to include the contributions due to space charge current and dark current as proposed and demonstrated in this study. Various other models and relevant fitting parameters are also evaluated and discussed in this article.     

溶胶-凝胶法制备铜锌锡硫薄膜及其太阳能电池的研究进展

原料丰富价廉的铜锌锡硫(Cu2ZnSnS4,CZTS)材料与非真空、低成本绿色溶胶-凝胶法相结合在产业化制造高性价比CZTS薄膜太阳能电池方面的应用引人关注。为了了解未来发展方向,综述了溶胶-凝胶法制备CZTS薄膜与器件的研究进展,讨论了不同溶胶-凝胶工艺途径、不同溶剂、硫化等对CZTS薄膜制备与器件特性的影响,分析了Na掺杂及硫化退火对CZTS薄膜的作用,并结合绿色制造的要求探讨了其发展趋势。     

Anisotropy of the spectroscopy properties of the wurtz-stannite Cu2ZnGeS4 single crystals

In this study, the near band edge anisotropic optical properties of wurtz-stannite (WS) Cu₂ZnGeS₄ single crystals were characterized using polarization-dependent transmittance and electrolyte electroreflectance (EER) techniques. Single crystals of Cu₂ZnGeS₄ were grown by chemical vapor transport method using iodine as a transport agent. Analysis of absorption spectra revealed indirect allowed transitions for Cu₂ZnGeS₄ with the band gaps of 2.02 (2.07) and 2.08 (2.14) eV for E‖b and Е‖a polarization configurations at 300 (10) K. The room-temperature EER spectra in the vicinity of the direct band edge showed anisotropic transitions at around 2.38, 2.44 and 2.45 eV for E‖b, Е‖a and Е‖c polarizations, respectively. Based on the experimental observations and recent band-structure calculations a plausible band diagram near band edge of WS-Cu₂ZnGeS₄ was constructed.     

Sphere-like kesterite Cu2ZnSnS4 nanoparticles synthesized by a facile solvothermal method

In this paper, sphere-like kesterite Cu₂ZnSnS₄ (CZTS) nanoparticles were successfully synthesized by a facile solvothermal method. The CZTS nanoparticles with diameter range of 100-150 nm were agglomerated by CZTS nanocrystals. The as-obtained CZTS nanoparticles were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission election microscopy (TEM), Energy Dispersive Spectrometry (EDS) and UV-vis spectroscopy. Texture structures with kesterite crystallinity were reflected from the X-ray diffraction of 112, 200 and 312 planes of the CZTS nanoparticles. The UV-vis absorption spectra showed that CZTS nanoparticles had strong absorption in the visible light region. The observed band gap of 1.48 eV matched well with the bulk CZTS material that was optimal for solar cells.