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.     

Thin-film solar cells

The rapid progress that is being made with inorganic thin-film photovoltaic (PV) technologies, both in the laboratory and in industry, is reviewed. While amorphous silicon based PV modules have been around for more than 20 years, recent industrial developments include the first polycrystalline silicon thin-film solar cells on glass and the first tandem solar cells based on stacks of amorphous and microcrystalline silicon films (“micromorph cells”). Significant thin-film PV production levels are also being set up for cadmium telluride and copper indium diselenide.     

Thin tantalum-silicon-oxygen/tantalum-silicon-nitrogen films as high-efficiency humidity diffusion barriers for solar cell encapsulation

Flexible thin-film solar cells require flexible encapsulation to protect the copper-indium-2 selenide (CIS) absorber layer from humidity and aggressive environmental influences. Tantalum-silicon-based diffusion barriers are currently a favorite material to prevent future semiconductor devices from copper diffusion. In this work tantalum-silicon-nitrogen (Ta-Si-N) and tantalum-silicon-oxygen (Ta-Si-O) films were investigated and optimized for thin-film solar cell encapsulation of next-generation flexible solar modules.CIS solar modules were coated with tantalum-based barrier layers. The performance of the thin-film barrier encapsulation was determined by measuring the remaining module efficiency after a 1000 h accelerated aging test. A significantly enhanced stability against humidity diffusion in comparison to non-encapsulated modules was reached with a reactively sputtered thin-film system consisting of 250 nm Ta-Si-O and 15 nm Ta-Si-N.     

Annealing studies and electrical properties of SnS-based solar cells

Thin films of SnS (tin sulphide) were thermally evaporated onto glass and CdS/ITO (cadmium sulphide/indium tin oxide) coated glass substrates and then annealed in vacuum with the aim of optimising them for use in photovoltaic solar cell device structures. The chemical and physical properties of the layers were determined using scanning electron microscopy, energy dispersive x-ray analysis, x-ray diffraction, and transmittance versus wavelength measurements. “Superstrate configuration” devices were also made using indium tin oxide as the transparent conductive oxide, thermally evaporated cadmium sulphide as the buffer layer and evaporated copper/indium as the back contact material. Capacitance-voltage data are given for the fabricated devices. Capacitance-voltage, spectral response and I-V data are given for the fabricated devices.     

Influence of substrate temperature on structural,optical, and electrical properties of flash evaporated CuIn0.81Al0.19Se2 thin films

Chalcopyrite copper indium aluminum diselenide (CuIn_0.81Al_0.19Se₂) compound is prepared by direct reaction of high purity elemental copper, indium, aluminum and selenium in their stoichiometric proportion. Structural and compositional characterizations of pulverized material confirm the formation of a single phase, polycrystalline nature. CuInAlSe₂ (CIAS) thin films are deposited on organically cleaned soda lime glass substrates using flash evaporation technique by varying the substrate temperatures in the range from 423 K to 573 K. Influence of substrate temperature observed by X-ray diffraction (XRD), scanning electron microscope (SEM), optical and electrical measurement. CIAS Films grown at different substrate temperatures are polycrystalline in nature, exhibiting a chalcopyrite structure with lattice parameters a = ∼0.576 nm and c = ∼1.151 nm. The crystallinity in the films increases with increasing substrate temperature up to 473 K, and tend to degrade at higher substrate temperatures. Optical band gap is in the range of 1.20 eV–1.38 eV and the absorption coefficient is close to 10⁵ cm⁻¹. Electrical characterization reveals p-type conductivity and the structural, morphological and optical properties indicate potential use of CIAS thin films as an absorber layer for thin film solar cell applications.     

Mechanical synthesis of high purity Cu–In–Se alloy nanopowder as precursor for printed CISe thin film solar cells

Mechanical alloying and ball milling are low cost, up-scalable techniques for the preparation of high purity chalcogenide nanopowders to be used as precursor material for printing thin film solar cells. In this study, high purity copper indium selenium (Cu–In–Se) alloy nanopowders with 20–200 nm particle size were synthesized from macroscopic elemental Cu, In and Se powders via mechanical alloying and planetary ball milling. The particle size distribution, morphology, composition, and purity level of the synthesized Cu–In–Se alloy nanopowders were investigated. Thin Cu–In–Se alloy nanopowder ink coatings, deposited on Mo-coated glass substrates by doctor blading, were converted into a CuInSe₂ semiconductor film by selenization heat treatment in Se vapor. The CuInSe₂ film showed semiconducting band gap around 1 eV measured by photoluminescence spectroscopy. CuInSe₂ absorber layer based thin film solar cell devices were fabricated to assess their performance. The solar cell device showed a total efficiency of 4.8%, as measured on 0.25 cm² area cell.     

Historical Analysis of High-Efficiency,Large-Area Solar Cells: Toward Upscaling of Perovskite Solar Cells

The status and problems of upscaling research on perovskite solar cells, which must be addressed for commercialization efforts to be successful, are investigated. An 804 cm² perovskite solar module has been reported with 17.9% efficiency, which is significantly lower than the champion perovskite solar cell efficiency of 25.2% reported for a 0.09 cm² aperture area. For the realization of upscaling high-quality perovskite solar cells, the upscaling and development history of conventional silicon, copper indium gallium sulfur/selenide and CdTe solar cells, which are already commercialized with modules of sizes up to ≈25 000 cm², are reviewed. GaAs, organic, dye-sensitized solar cells and perovskite/silicon tandem solar cells are also reviewed. The similarities of the operating mechanisms between the various solar cells and the origin of different development pathway are investigated, and the ideal upscaling direction of perovskite solar cells is subsequently proposed. It is believed that lessons learned from the historical analysis of various solar cells provide a fundamental diagnosis of relative and absolute development status of perovskite solar cells. The unique perspective proposed here can pave the way toward the upscaling of perovskite solar cells.     

Preparation and characteristics of CuInSe2 thin films by dip-coating method using its nanocrystal ink

Nanocrystal ink-coating technique is a low cost, less pollution, and non-vacuum solution based processing to produce CIS absorbing layers for photovoltaics, leading to low fabrication cost and eco-friendly process of solar cells. In this work, highly crystallized chalcopyrite CuInSe₂ (CIS) nanocrystals were synthesized by a green and cheap air pressure hot injection method using 1-Methyl-2-pyrrolidinone and glycerol mixed solvent, and copper chloride, indium chloride and selenium dioxide as precursors. The synthesized CIS nanocrystals were used to prepare colloidal nanocrystal inks by dispersing them ultrasonically in absolute alcohol and deposit CIS thin films by dip-coating nanocrystal inks. Basic characterization data of the synthesized CIS nanocrystals and the ink-coated thin films were described by XRD, TEM, FESEM, EDS, UV–vis–NIR, and Hall measurements.     

CuIn1 − xGaxSe2 photovoltaic devices for tandem solar cell application

CuIn_1 − xGa_xSe₂ (CIGS) solar cells show a good spectral response in a wide range of the solar spectrum and the bandgap of CIGS can be adjusted from 1.0 eV to 1.7 eV by increasing the gallium-to-indium ratio of the absorber. While the bandgaps of Ga-rich CIGS or CGS devices make them suitable for top or intermediate cells, the In rich CIGS or CIS devices are well suited to be used as bottom cells in tandem solar cells. The photocurrent can be adapted to the desired value for current matching in tandem cells by changing the composition of CIGS which influences the absorption characteristics. Therefore, CIGS layers with different [Ga]/[In + Ga] ratios were grown on Mo and ZnO:Al coated glass substrates. The grain size, composition of the layers, and morphology strongly depend on the Ga content. Layers with Ga rich composition exhibit smaller grain size and poor photovoltaic performance. The current densities of CIGS solar cells on ZnO:Al/glass varied from 29 mA cm^− 2 to 13 mA cm^− 2 depending on the Ga content, and 13.5% efficient cells were achieved using a low temperature process (450 °C). However, Ga-rich solar cells exhibit lower transmission than dye sensitized solar cells (DSC). Prospects of tandem solar cells combining a DSC with CIGS are presented.     

Zinc Thiolate Enables Bright Cu‐Deficient Cu‐In‐S/ZnS Quantum Dots

Copper indium sulfide (CIS) colloidal quantum dots (QDs) are a promising candidate for commercially viable QD‐based optical applications, for example as colloidal photocatalysts or in luminescent solar concentrators (LSCs). CIS QDs with good photoluminescence quantum yields (PLQYs) and tunable emission wavelength via size and composition control are previously reported. However, developing an understanding and control over the growth of electronically passivating inorganic shells would enable further improvements of the photophysical properties of CIS QDs. To improve the optical properties of CIS QDs, the focus is on the growth of inorganic shells via the popular metal‐carboxylate/alkane thiol decomposition reaction. 1) The role of Zn‐carboxylate and Zn‐thiolate on the formation of ZnS shells on Cu‐deficient CIS (CDCIS) QDs is studied, 2) this knowledge is leveraged to yield >90% PLQY CDCIS/ZnS core/shell QDs, and 3) a mechanism for ZnS shells grown from zinc‐carboxylate/alkane thiol decomposition is proposed.     

Well-aligned ZnO nanorod arrays from diameter-controlled growth and their application in inverted polymer solar cell

Well-aligned ZnO nanorod arrays (ZNAs) with various growth time were fabricated on indium tin oxide (ITO) coated glass substrate using hydrothermal method. The average diameter of the ZnO nanorods ranged from 35 to 100 nm with elongating growth time from 0.5 to 3 h. The ZNAs had wurtzite-structured (hexagonal) ZnO and preferred growth along (0001) direction. When growth time was less than 2 h, the ZNAs showed very high optical transmission (>80%) in visible light region. The formation of Ohmic contact between ZNAs and the substrates was also observed. Furthermore, solar cells consisted of ZNAs/polymer hybrid were fabricated, and a highest power conversion efficiency (PCE) of 1.11% from these devices was achieved. Moreover, The PCE of this device almost remained constant for long time when exposed to ambient atmosphere.     

Junction formation of CuInSe2 with CdS: A comparative study of “dry” and “wet” interfaces

The junction formation of polycrystalline CuInSe₂ absorbers (CIS) with thermally evaporated CdS was investigated by high-resolution synchrotron X-ray photoelectron spectroscopy. The chemistry and electronics of the interfaces of Cd partial electrolyte treated CIS (“wet” processed) and clean, decapped CIS (“dry” processed) were compared. A valence band offset of 0.96(10) eV was determined in both cases. The Cd(Se,OH) surface layer induced by the wet Cd partial electrolyte process does not significantly modify the band alignment at the CIS/CdS heterointerface from the “dry”, vacuum-processed CIS/CdS interface.During the stepwise interface formation the energy converting capability of the CIS/CdS heterojunction was assessed by in situ surface photovoltage measurements at room temperature. The evolution of the surface photovoltage significantly differs for the “wet” and the “dry” interfaces and is discussed in relation to the function in solar cell devices.     

A solvothermal approach for the size-, shape- and phase-controlled synthesis and properties of CuInS2

In this work, Copper Indium disulfide (CIS) nanoparticles of size ∼ 5 nm were prepared via solvothermal approach in ethanol under the nitrogen atmosphere using copper chloride, indium chloride and thiourea (Tu) as starting materials, without any assistance through organic ligands at the reaction temperature of 150 °C. The factors which might affect the morphology, structure, phase of the product during the synthesis were discussed. It was found that the products were significantly affected by the reaction time and solvent. The morphology, structure, phase constituents and optical properties of the as prepared CIS powders were characterized by X-ray diffraction (XRD), Energy dispersive Spectroscopy (EDS), scanning electron microscopy (SEM) and ultraviolet–visible (UV–Vis) spectrometry respectively. The result shows that the CIS nanoparticles can be synthesized by solvothermal method at a reaction time of 2 h and shows that when the reaction time was increased from 2 h to 48 h, CIS porous flower like nanoparticles were obtained as we increase the reaction time. We also observed that in this process, the phase selection of WZ-CIS or CH-CIS is greatly influence by solvent. We also observed that, in this process sulfur source did not influence the phase but participated in the growth of the nanoparticles.     

Structural properties of Cu(In,Ga)Se2 thin films prepared from chemically processed precursor layers

We have developed a chemical process for incorporating copper into indium gallium selenide layers with the goal of creating a precursor structure for the formation of copper indium gallium diselenide (CIGS) photovoltaic absorbers. Stylus profilometry, EDX, Raman spectroscopy, XRD and SIMS measurements show that when indium gallium selenide layers are immersed in a hot copper chloride solution, copper is incorporated as copper selenide with no increase in the thickness of the layers. Further measurements show that annealing this precursor structure in the presence of selenium results in the formation of CIGS and that the supply of selenium during the annealing process has a strong effect on the morphology and preferred orientation of these layers. When the supply of Se during annealing begins only once the substrate temperature reaches ≈ 400 °C, the resulting CIGS layers are smoother and have more pronounced preferred orientation than when Se is supplied throughout the entire annealing process.     

Immobilization of copper indium selenide solar module waste in concrete constructions

The aim of this study was to investigate the properties of concrete containing various quantities of copper indium selenide (CIS) solar module waste by replacing a certain part (up to 40%) of sand. The obtained results have shown that an increase in the content of solar module waste resulted in an increase of the density of fresh and hardened concrete. The compressive strength of the specimens compared to the control specimens has been higher, when sand aggregate was replaced by CIS solar module waste particles from 5 to 20%. Also, a decrease in the water absorption and porosity of concrete specimens containing immobilized waste compared to those with no waste has been observed. The leaching behaviour of the concrete containing immobilized waste was also studied. The results showed that the concrete with sand aggregate replacement by waste particles between 5 and 10% has the best leaching properties. That replacement can be used for CIS solar module waste recycling in concrete production.     

Electrodeposition of wide band gap InGaxSyOz thin films for solar cell applications

Indium-Gallium-sulfide-oxide thin films were deposited onto F-doped SnO₂-coated glass by electrochemical deposition from an aqueous bath. The films were deposited at three different ratios of gallium to indium in the precursor bath; namely [Ga/In] = 2/8, 5/5 and 8/2. The impact of the gallium content on the composition, optical transmission, structure, photosensitivity, electrical resistivity and morphology of the deposited films was investigated. The films deposited at [Ga/In] = 5/5 and 8/2 had an energy gap as high as 3.5 eV. The X-ray diffraction spectrum of the film deposited at [Ga/In] = 2/8 contained weak peaks of indium metal, but the In peaks were absent in the spectra of the films deposited at [Ga/In] = 5/5 and 8/2. The photosensitivity of the film was observed by means of photoelectrochemical measurements, which confirmed that all the films showed n-type conduction. Finally, the film has been used as a buffer layer to fabricate a SnS-based thin film solar cell.     

Comparative study of sputtered and electrodeposited CI(S,Se) and CIGSe thin films

Copper indium disulphide CuInS₂ (CIS) and diselenide CuInSe₂ (CISe) and their alloys with gallium CuIn_1 − xGa_xSe₂ (CIGSe) thin films have been prepared using both high- and non-vacuum processes. The well known two-stage process consisting in a sequential sputtering of Cu and In thin layers and a subsequent sulfurisation has led to the formation of good quality CuInS₂ ternary compound. The films exhibit the well known chalcopyrite structure with a preferential orientation in the (112) plane suitable for the production of the efficient solar cells. The absorption coefficient of the films is higher than 10⁴ cm^− 1 and the band gap value is about 1.43 eV. A non-vacuum technique was also used. It consists on a one step electrodeposition of Cu, In and Se and in a second time Cu, In, Se and Ga. From the morphological and structural point of view, the films obtained are similar to those prepared by the first technique. The band gap value increases up from 1 eV for the CIS films to 1.26 eV for the CuIn_1 − xGa_xSe₂ with 0 < x < 0.23. The resistivity at room temperature of the films was adjusted to 10 Ωcm after annealing. The films exhibit an absorption coefficient more than 10⁵ cm^− 1. The most important conclusion of this study is the interesting potential of electrodeposition as a promising option in low-cost CISe and CIGSe thin film based solar cells processing.     

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.     

The influence of annealing temperature on the structural, electrical and optical properties of ion beam sputtered CuInSe2 thin films

CuInSe₂ (CIS) thin films were prepared by ion beam sputtering deposition of copper layer, indium layer and selenium layer on BK7 glass substrates followed by annealing at different temperatures for 1 h in the same vacuum chamber. The influence of annealing temperature (100-400 °C) on the structural, optical and electrical properties of CIS thin films was investigated. X-ray diffraction (XRD) analysis revealed that CIS thin films exhibit chalcopyrite phase and preferential (112) orientation when the annealing temperature is over 300 °C. Both XRD and Raman show that the crystalline quality of CIS thin film and the grain size increase with increasing annealing temperature. The reduction of the stoichiometry deviation during the deposition of CIS thin films is achieved and the elemental composition of Cu, In and Se in the sample annealed at 400 °C is very near to the stoichiometric ratio of 1:1:2. This sample also has an optical energy band gap of about 1.05 eV, a high absorption coefficient of 10⁵ cm⁻¹ and a resistivity of about 0.01 Ω cm.     

Analysis of single junction a-Si:H solar cells grown on different TCO’s

In consequence of previous investigation of individual transparent conductive oxide (TCO) and absorber layers a study was carried out on hydrogenated amorphous silicon (a-Si:H) solar cells with diluted intrinsic a-Si:H absorber layers deposited on glass substrates covered with different TCO films. The TCO film forms the front contact of the super-strata solar cell and has to exhibit good electrical (high conductivity) and optical (high transmittance) properties. In this paper we focused our attention on the influence of using different TCO’s as a front contact in solar cells with structure as follows: Corning glass substrate/TCO (800, 950 nm)/p-type μc-Si:H (∼5 nm)/p-type a-Si:H (10 nm)/a-SiC:H buffer layer (∼5 nm)/intrinsic a-Si:H absorber layer with dilution R = [H₂]/[SiH₄] = 20 (300 nm)/n-type a-Si:H layer (20 nm)/Ag + Al back contact (100 + 200 nm). Diode sputtered ZnO:Ga, textured and non-textured ZnO:Al [3] and commercially fabricated ASAHI (SnO₂:F) U-type TCO’s have been used. The morphology and structure of ZnO films were altered by reactive ion etching (RIE) and post-deposition annealing.It can be concluded that the single junction a-Si:H solar cells with ZnO:Al films achieved comparable parameters as those prepared with commercially fabricated ASAHI U-type TCO’s.