Photoconductivity effects in CuInS2, CuInSe2 and CuInTe2 thin films

Photoconductivity response spectra for CuInS₂, CuInSe₂ and CuInTe₂ thin films are reported. The temperature dependences of the spectra are utilized to determine the bandgap energies as functions of temperature. Photoconductive response times are measured for these I–III–VI₂ ternary semiconductors and are discussed in terms of deposition parameters and post-deposition treatments. The photoconductive decay times are in the range 10^-3 – 10¹ ms.     

TiO2/CuInS2复合纳米棒阵列的制备及其光电性能

采用两步溶剂热法在氧化氟锡(FTO)导电玻璃基底上制备了CuInS2敏化TiO2纳米棒阵列复合薄膜光阳极.利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)表征了复合阵列薄膜的晶体结构和表面形貌,同时采用紫外可见吸收分光光度计(UV-Vis)及光电流电压(I-V)曲线研究了CuInS2敏化TiO2纳米阵列薄膜的光学及光电化学性质.研究结果表明,TiO2纳米棒阵列薄膜被CuInS2敏化后在可见光区的吸收有明显的增强.在模拟太阳光照射下(100 mW/cm2),利用这种复合薄膜作为光阳极组装的量子点敏化太阳能电池的开路电压为0.29 V,短路电流密度为0.15 mA/cm2,具有一定的光电转换能力.     

Optical constants of Zn-doped CuInS2 thin films

Optical properties of Zn-doped CuInS₂ thin films grown by double source thermal evaporation method have been studied. The amount of the Zn source was determined to be 0%-4% molecular weight compared with CuInS₂ source. After that, samples were annealed in vacuum at the temperature of 450 °C in quartz tube. The optical constants of the deposited films were obtained from the analysis of the experimental recorded transmission and reflexion spectral data over the wavelength range 300-1800 nm. It is observed that there is an increase in optical band gap with increasing Zn % molecular weight. It has been found that the refractive index and extinction coefficient are dependent on Zn incorporation. The complex dielectric constants of Zn-doped CuInS₂ films have been calculated in the investigated wavelength range. It was found that the refractive index dispersion data obeyed the single oscillator of the Wemple-DiDomenico model, from which the dispersion parameters and the high-frequency dielectric constant were determined. The electric free carrier susceptibility and the carrier concentration on the effective mass ratio were estimated according to the model of Spitzer and Fan.     

Progress in the development of CuInS2 based mini-modules

A sequential process is used to synthesise CuInS₂ absorber layers for photovoltaic application. In this process CuIn precursor layers sputtered on molybdenum coated float glass are converted to CuInS₂ via sulphurisation in an elemental sulphur vapour ambient. A re-evaluation of process parameters has been performed including fine tuning of numerous minor aspects. Using optimised process conditions has led to improved device performance, especially a narrowed distribution at higher module efficiencies is achieved. At the same time the process yield is improved resulting in fewer devices with poor electrical quality.     

Sulphurization of single-phase Cu11In9 precursors for CuInS2 solar cells

Using Rutherford backscattering (RBS), X-ray diffraction (XRD), and scanning electron microscopy (SEM), the sulphurization of single-phase Cu₁₁In₉ precursors to be employed as light absorbing CuInS₂ (CIS) layers in CIS-CdS heterojunction thin-film solar cells has been investigated. The Cu₁₁In₉ precursor films were produced by DC-sputtering from a single-phase Cu₁₁In₉ target. The sulphurization at 500 or 300 °C was performed by adding different amounts of elemental sulphur with heating rate and sulphurization time as additional parameters. During sulphurization at 500 °C, up to 50% of the indium initially present in the precursor is lost. We relate the In-loss to the volatile In₂S compound, the formation of which is favoured by the phase transition of Cu₁₁In₉ to Cu₁₆In₉ at 307 °C. Consequently, the In-loss can be suppressed by employing a sulphurization temperature of 300 °C. At this temperature, a prolonged sulphurization time and a large sulphur excess are necessary in order to obtain stoichiometric CIS beneath a CuS_x surface phase.     

CuInS2 thin films deposited by sol-gel spin-coating method

CuInS₂ thin films were prepared using a sol-gel spin-coating method. Copper acetate monohydrate (Cu(CH₃COO)₂·H₂O) and indium acetate (In(CH₃COO)₃) were dissolved into 2-propanol and 1-propanol, respectively. The two solutions were mixed into a starting solution. The solution was dropped onto glass substrate, rotated at 1500 rpm, and dried at 300 °C for Cu-In as-grown films. The as-grown films were sulfurized inside a graphite container box. A clear chalcopyrite phase was observed without a secondary phase. Surface roughness of the films sulfurized at 500 °C was 19.1 nm. A Raman spectra measurement confirmed that no Cu-S or In-S compounds were created in the thin films.     

One-pot route for preparation of monodisperse CuInS2 nanocrystals

Chalcopyrite copper indium sulfide (CuInS₂) nanocrystals (NCs) were synthesized by a one-pot route and characterized by XRD, TEM, HRTEM, EDS, UV-vis and SPS. The experimental results demonstrated that the CuInS₂ NCs synthesized by metal compound [Sn(acac)₂Cl₂] had good crystallinity, monodispersity and stoichiometric composition. The UV-vis absorption spectra showed the as-synthesized CuInS₂ NCs had fine absorption in the visible light region and the energy band gap was estimated to be 1.58 eV. Moreover, the metal compound could improve the photoinduced charge separation and transfer effect of NCs based on the SPS study. The synthesis strategy developed in this work may be used as a general process for the synthesis of pure or doped chalcogenide NCs, and may have great potential to be applied in high efficiency, yet low cost photovoltaic areas.     

Characteristics of stacked CuInS2 and CuGaS2 layers as determined by the growth sequence

CuInS₂ and CuGaS₂ thin films have been prepared sequentially from elemental evaporation sources onto conventional soda lime glass substrates heated at 350 °C during the deposition process. The gradient in the structure and composition of the stacked layers has been investigated for the two possible growth sequences. Structural depth profiling and crystallographic phase analysis were performed by grazing incidence X-ray diffraction. The atomic distribution in the films depth was analyzed by X-ray photoelectron spectroscopy combined with sputter etching. Formation of the quaternary compound CuIn_1 − xGa_xS₂, with a high Ga content x > 0.80, has been detected with different distribution depending on the growth sequence.     

The verification of the existence of TiS2

The intrinsic electronic properties of TiS₂ are currently under some debate. It has not been conclusively demonstrated if TiS₂ is a semimetal or a degenerate semiconductor. We have thoroughly studied this problem by first characterizing the material composition and then determining the electronic properties. Precision x-ray diffraction, mass density, and chemical analysis have been used to characterize TiS₂. Trends in the Ti_xS₂ series of nonstoichiometric compounds have been monitored by intercalation, scanning electron microscope, magnetic susceptibility and electron transport measurements. We conclude from the total body of data collected that TiS₂ exists as a stoichiometric compound and that its semimetallic properties are intrinsic.     

The fabrication of hollow cubic-like CuInS2 cages using Cu2O crystals as sacrificing template

Hollow cubic-like CuInS₂ cages were prepared with cubic Cu₂O nanocrystals as self-sacrificing template through solvothermal process. The formation of these hollow structures could be attributed to the migration of copper ions and the copy of cubic Cu₂O template based on the Kirkendall effect and the Ostwald ripening process. Such process and mechanism might be extended to synthesize other hollow ternary chalcogenide materials.     

Epitaxial growth of ZnO on CuInS2(112)

We report on epitaxial growth of ZnO on (112) orientated CuInS₂ thin films. Step-by-step growth and investigation by photoelectron spectroscopy (PES) and low energy electron diffraction (LEED) provided information on the growth mode and the electronic structure of the ZnO-CuInS₂-interface. During the initial growth no ZnO is deposited. Instead a monolayer of ZnS is formed by depletion the CuInS₂ surface of excess sulfur. Thereafter, the ZnO growth starts on the ZnS buffer layer. The band alignment derived from PES shows that the ZnS buffer layer is thin enough to provide a beneficial band alignment for photovoltaic applications.     

Preparation of CuInS2 microspheres via a facile solution-chemical method

With a mixed solvent of triethylenetetramine-ethylene glycol (1:1, v/v), CuInS₂ microspheres were synthesized by a facile solution-chemical method under the open-air condition. Morphology, structure, phase constituents and optical properties of the as-prepared CuInS₂ powders were characterized by X-ray diffraction (XRD), Energy Dispersive Spectrometer (EDS), scanning electron microscope (SEM) and ultraviolet-visible (UV-vis) spectrophotometry. The characterizations showed that the synthesized CuInS₂ powders had single phase, good crystallinity and stoichiometric composition. Moreover, the prepared CuInS₂ powders showed microspheres with the size from 200 to 400 nm, and their energy band gaps were 1.52 eV, which made them promising candidates as absorber materials for photovoltaic applications.     

Structure and phase relations in the 2(CuInS2)-Cu2ZnSnS4 solid solution system

The intermixing of roquesite (CuInS₂) and kesterite (Cu₂ZnSnS₄), i. e. Cu(In_x(ZnSn)_1−xS₂ was investigated by a combination of neutron and X-ray powder diffraction. Samples with 0 ≤ × ≤ 1 were synthesized by a solid state reaction of the pure elements in evacuated silica tubes at 800 °C and cooled with a 10 K/h rate after the final annealing. The structural parameters of CuIn_x(ZnSn)_1−xS₂ were determined by simultaneous Rietveld refinement of neutron and X-ray diffraction data. The microstructure and chemical composition of the samples were investigated by electron microprobe analysis. A broad miscibility gap exists in the region 0.4 ≤ × < 0.8 indicated by the coexistence of two phases, an In-rich (x ~ 0.77) and a Zn-Sn-rich (x ~ 0.33) phase. Cu(In_x(ZnSn)_1−xS₂ mixed crystals with 0 ≤ x < 0.4 crystallize in the kesterite type structure, and with 0.8 ≤ × ≤ 1.0 in the chalcopyrite type structure. In the latter In, Zn and Sn are disordered on the In site. In the mixed crystals the lattice constant a and c show a linear dependence on chemical composition, whereas the tetragonal deformation Δ = 1−c/2a varies nonlinearly. Moreover in the mixed crystal with x ~ 0.15 the tetragonal deformation is equal zero and thus its structure is characterized by a pseudo-cubic unit cell.     

Addition of Na into CuInS2 thin film via co-evaporation

While most of studies focus on the addition of Na into CuInGaSe₂ as well as CuInGaS₂ thin films, this study examines the addition of Na into CuInS₂ (CIS) thin films. Moreover, an alternative approach has been used to incorporate Na into CIS thin films. Two source evaporation (Cu and In) was first performed to obtain Cu-In layers with desired thicknesses. Three source evaporation (Cu, In, and NaF) then followed subsequently to produce Na-doped Cu-In precursor films having different Na concentrations. The precursor films were immediately sulfurized in the same evaporation chamber to form CIS thin films. The addition of Na was found to enhance (112) preferred orientation and reduce the grain size. Raman spectra show that the addition of Na does not alter the needed phase transformation from CuInS₂-CuAu structure to CuInS₂-chalcopyrite structure during the sulfurization. Blue shift of the CIS Raman CH mode occurs as a result. The doping of Na was also found to decrease the film resistivity or increase the hole concentration in the films.     

Heteroepitaxial growth of GaP layers on CuInS2 and their characterization

Epitaxial GaP layers were grown on CuInS₂ single-crystal substrates by chemical vapour transport. The preparation and thermal treatments of the substrate are briefly described. The condtions for the growth of single-crystal GaP layers were determine. The surface morphology and structural properties of the as-grown layers and the electrical characteristics of the n-GaP/p-CuInS₂ heterojunctions are reported. Tunnelling was determined to be the main conduction mechanism in this heterojunction, and a band diagram is proposed.     

Fabrication of hollow-sphere films of wurtzite CuInS2 on copper substrate

As important semiconductors, I–III–VI₂ compounds have attracted wide attention, among which the wurtzite structured CuInS₂ has been the research focus due to its metastable phase. In this paper, the wurtzite CuInS₂ hollow-sphere films have been successfully prepared on copper substrate in a self-designed solvothermal detached system. The films of Cu(OH)₂ one-dimensional nanostructure arrays and thioacetamide were used as the precursors and triethylene glycol was used as the solvent. Experiments showed that the amount of indium trichloride played a determinative role in the final morphology of the products. Meanwhile, the one-dimensional nanostructure arrays and the detached solvothermal system have great influences on the crystal shape as well. Based on the experimental results, a possible formation mechanism for the CuInS₂ hollow spheres was also proposed. The UV–Vis absorption spectrum showed a broad absorption over the entire visible light and extending into the near-infrared region and presented the band gap of 1.53 eV for the as-prepared wurtzite CuInS₂, which indicates the potential applications in solar cells.     

CuInS2 thin films obtained by spray pyrolysis for photovoltaic applications

Copper indium disulphide, CuInS₂, is a promising absorber material for thin film photovoltaic which has recently attracted considerable attention due to its suitability to reach high efficiency solar cells by using low-cost techniques. In this work CuInS₂ thin films have been deposited by chemical spray pyrolysis onto glass substrates at ambient atmosphere, using different composition solutions at various substrate temperatures. Structural, chemical composition and optical properties of CIS films were analysed by X-ray diffraction, energy dispersive X-ray spectroscopy and optical spectroscopy. Sprayed CIS films are polycrystalline with a chalcopyrite structure with a preferential orientation along the <112> direction and no remains of oxides were found after spraying in suitable conditions. X-ray microanalysis shows that a chemical composition near to stochiometry can be obtained. An optical gap of about 1.51 eV was found for sprayed CIS thin films.     

A mild solvothermal route for preparation of cubic-like CuInS2 crystals

A mild solvothermal route for preparation of cubic-like CuInS₂ crystals was developed by using benzyl alcohol as the reaction medium and In(NO₃)₃·9H₂O, CuCl₂·2H₂O and thiourea as the precursors. The as-synthesized CuInS₂ crystals were characterized by XRD, XPS, SEM, and TEM. The characterizations showed that the synthesized CuInS₂ crystals had stoichiometric composition and good crystallinity. Moreover, the prepared CuInS₂ crystals show good cubic-like morphology with the size from 100 to 200 nm.     

CuInS2量子点敏化太阳能电池材料的研究进展

CuInS_2量子点因低毒、良好的光电性能和热电稳定性而成为量子点敏化太阳能电池(QDSSC)极具前景的量子点敏化剂。首先简单介绍了CuInS_2量子点材料的光电性质和QDSSC中CuInS_2量子点的合成,然后重点总结了CuInS_2量子点敏化电极的制备及各电池材料对QDSSC性能的影响,最后指出了该电池目前存在的问题以及对未来的展望。     

Polymorphous transformations in Cu-In-VI2 compounds and CuInS2xSe2(1−x) solid solutions

The thermal expansion of the Cu-In-VI₂ ternary compounds and CuInS_2xSe_2(1?x) solid solutions in the temperature range from 77 to 1200 K has been investigated by a quartz dilatometer. The phase transformations have been detected and confirmed by DTA on powder samples. It is shown that these phase transformations are the ones of the first type.