Copper Indium Gallium Diselenide Layer Research Articles

Effects of Layer Thickness on the Residual Stresses of CIGS Solar Cells with Polyimide Substrate

In this paper, we investigate the effect of layer thickness on the residual stresses of copper indium gallium diselenide (CIGS) solar cells with polyimide substrate caused by CIGS layer deposition at 400?C and then cooling down to room temperature using the Finite Element Method (FEM). Moreover, we also examined the effect of layer thickness on residual stress of CIGS solar cells after cooling down to room temperature from the hotspot temperatures of 200?C, 300?C, and 400?C. Our simulated CIGS is composed of five layers: ZnO, CdS, CIGS, Mo, and PI substrate. We were able to quantify the effect of each layer’s thickness and hotspot temperature on the average stresses of each layer for the CIGS solar cells. We found that the PI substrate layer has the most significant effect on the residual stress of CIGS solar cells. Our simulation results reveal that the stress type (tensile vs. compressive) and the magnitude of stress of the CIGS layer (main absorber layer) can be controlled by changing the thickness of the PI substrate while applying a heat to CIGS solar cells. Quantitative analysis of relationship between layer thickness and thermo-mechanical stress of thin film solar cells can help solar cell manufacturers design more robust and reliable solar cells. For example, fabricating PI layer thickness less than 17 μm can improve the performance of CIGS solar cells by nullifying the compressive residual stress in the CIGS absorber layer.

Optimized CIGS based solar cell towardsan efficient solar cell: impact of layers thickness and doping

This paper presents a numerical simulation study of copper-indium-gallium-diselenide (CIGS) thin film solar cells. An electron back reflector layer (EBR) is added to the conventional CIGS structure to minimize the recombination of the carriers at the back contact, and then absorber thickness can be further decreased. The impacts of thickness and carrier concentration variations of the CIGS cell structure are investigated to optimize the performance of the solar cell using the simulator SCAPS. The proposed CIGS solar cell achieved a significant improvement in the conversion efficiency of 27.652%, which is more than 43% higher than those previously reported in the literature for the CIGS solar cells. The proposed work does not only greatly improve the efficiency but also the overall thickness of the CIGS layers are dramatically decreased to 505 nm. That is already 3 to 4 times less than the average thickness reported for the conventional CIGS solar cells.

Defect states and grading induced bandgap variability analysis of CIGS solar cells through device simulations

Copper-indium-gallium-diselenide (CIGS) is one of the promising absorbing material in thin film solar cells. It is a direct band gap material with the band gap (Eg) ranging from 0.98 to 1.68 eV. The band gap of this material is dependent on the composition of the material. The band gap enhancement leads to significant reduction in the extent of exciton recombination but on the other hand it also reduces the absorption in the absorber layer. We simulated and analyzed the effect of band gap variations in CIGS layer, induced by grading of doping concentration profile and defect states over the performance of solar cell. The performance analysis has been done using SCAPS-1D (Solar Cell Capacitance Simulator) simulator. It is intended to develop specially to simulate the AC and DC characteristics of hetero-junction thin film solar cells, especially CIGS and CdTe solar cells. By the introduction of grading in the CIGS material, an enhancement of 2.48% has been observed in the overall efficiency. This enhancement can be attributed to the reduction in recombination and increase in the exciton generation.

Thin film solar cell efficiency enhancement using a gradient doping absorbent layer

In this contribution, we propose a numeric exploration of a copper indium gallium diselenide (CIGS) based thin film solar cell structure by means of SILVACO's technology computer aided design (T-CAD). We found the performance of our proposed cell and that of experimental champion very similar. High resistance and surface recombination near the rear contact alongside with bulk recombination reduce solar cell performance. In order to get a cell performance enhancement, we suggest the introduction of an additional electric field via gradient doping in absorbent layer in order to reduce the latter phenomenon effects. Therefore, both graded and uniform doping profiles have been studied then compared. Our results demonstrated that the graded doping in CIGS absorbent layer gives higher conversion efficiency (η) than uniform one. Structure with 0.11, 0.04, 0.01, and 2 μm thicknesses of MgF2, n-ZnO, n-CdS, and p-CIGS layers, respectively, gives the best performance. A graded doping of (3 × 1016-1022) cm−3 concentration in CIGS layer, 1022 cm−3 in ZnO layer, and 1021 cm−3 in CdS layer give a conversion efficiency of 29.43% in comparison to 22.92% of the proposed cell at room temperature.

Modeling Thermo-Mechanical Stress of Flexible CIGS Solar Cells

Copper indium gallium diselenide (CIGS) thin-film solar cells are fabricated through several deposition and annealing processes at high temperatures, which can generate significant thermal residual stress to solar cells. Moreover, since CIGS solar cells with flexible substrates are rollable and bendable, they are susceptible to mechanical stresses during these processes. In addition, partial shading (hotspot) can exert high heat on the CIGS solar cell. In this paper, we investigate the thermo-mechanical stress of each active layer of CIGS solar cells due to annealing, external bending, and hotspot using finite element method (FEM). We found that average stress of each active layer decreases and maximum stress in the cell increases when interface crack is introduced between cadmium sulfide (CdS)/CIGS. Our overarching goal is to quantify the relationship between the fabrication/operating process and the reliability of CIGS solar cells (energy release rate and internal stresses), which could improve the reliability of flexible solar cells. It is also found that lowering the annealing temperature can reduce the stresses in the cells and lowering CIGS thickness can reduce the delamination probability of CdS/CIGS interface. Finally, we investigate the effect of the crack length of the CdS/CIGS interface on the electrical performance of CIGS solar cells through FEM simulations. We found that as the crack size between CdS and CIGS layers increases, short-circuit current density decreases, while open-circuit voltage remains almost constant.

Confinement – assisted shock-wave-induced thin-film delamination (SWIFD) of copper indium gallium diselenide (CIGS) on a flexible substrate

The laser structuring of CIGS (copper indium gallium (di)selenide) solar cell material without influence and damaging the functionality of the active layer is a challenge for laser methods The shock-wave-induced thin-film delamination (SWIFD) process allows structuring without thermal modifications due to a spatial separation of the laser absorption from the functional layer removal process. In the present study, SWIFD structuring of CIGS solar cell stacks was investigated. The rear side of the polyimide was irradiated with a KrF-Excimer laser. The laser-induced ablation process generates a traverse shock wave, and the interaction of the shock wave with the layer-substrate interface results in a delamination process. The effect of a water confinement on the SWIFD process was studied where the rear side of the substrate was covered with a ∼2mm thick water layer. The resultant surface morphology was analysed and discussed. At a sufficient number of laser pulses N and laser fluences Φ, the CIGS layer can be selectively removed from the Mo back contact. The water confinement, as well as the increasing laser beam size A0 and N, results in the reduction of the necessary minimal laser fluence Φth. Further, the delaminated CIGS area increased with increasing Φ, N, and A0.

Life cycle assessment of photovoltaic manufacturing consortium (PVMC) copper indium gallium (di)selenide (CIGS) modules

Thin film copper indium gallium (di)selenide (CIGS) photovoltaic (PV) modules show promise for significant growth. The Photovoltaics Manufacturing Consortium (PVMC) is leading research and development of CIGS in New York State. This study presents the results of a life cycle assessment (LCA) study of CIGS technology, currently being advanced by PVMC, and compares the environmental performance of several emerging alternative materials and processes. The results provide manufacturers with an understanding of how to produce CIGS sustainably. The cradle-to-gate LCA study followed the International Standards Organization (ISO) 14040 series. In addition to analyzing CIGS cells, the study evaluated zinc oxysulfide (Zn(O,S)) as an alternative for cadmium sulfide (CdS) for the junction partner, and an integrated cell interconnect (ICI) system as an alternative for the screen printing and stringer. Life cycle inventory data for the CIGS cell and alternatives were obtained from PVMC for the product manufacturing stage. Global Solar Energy, Inc. (GSE), a PVMC member and CIGS manufacturer, provided data for the ICI alternative. This data was supplemented by secondary data, from thinkstep, and modeled in GaBi6. The end-of-life stage was not modeled due to limited inventory data. The results identified the following key drivers of environmental and toxicity impacts from the manufacture of CIGS photovoltaic cells: (i) silver used in the stringer and screen printing processes, (ii) metals comprising the CIGS layer, (iii) surface washing of the stainless steel substrate, and (iv) copper in the cable for the balance of system. In addition, the study found that the zinc oxysulfide alternative had lower overall impacts compared to cadmium sulfide. Substitution of the ICI system also reduced impacts of the CIGS system, by decreasing the silver needed. Finally, comparison of the overall life cycle impact results to similar systems in literature, which focused primarily on greenhouse gas emissions, found that the CIGS system fell in the lower end of the range of estimated global warming impacts. PVMC’s CIGS module impacts are likely lower than those made by other manufacturers due to their use of a stainless steel versus glass substrate and reliance on a relatively clean energy mix in New York State. To further reduce impacts, PVMC may wish to substitute the ICI component for the stringer and screen printing processes, recycle additional waste materials, substitute recycled metals for virgin materials, and substitute the cadmium sulfide with the zinc oxysulfide alternative.

Mechanistic Study of One-Step Cathodic Electrodeposition of Mixed Cu-In-Ga Oxide/Hydroxide Films with Hydrogen Peroxide Oxygen Precursor

Electrodeposition of multicomponent oxide films with semiconducting properties for use in various applications like photovoltaics is of great interest. This paper deals with mixed copper, indium, gallium oxides which can be used as precursors for copper indium gallium diselenide layer in thin film solar cells and potentially p-type transparent oxide layers, in the delafossite family. One-step cathodic electrodeposition of Cu-In-Ga mixed oxide/hydroxide is investigated using hydrogen peroxide as the oxygen source. The deposition mechanism of the Cu-In-Ga oxide layers is studied by cyclic voltammetry and in situ using an electrochemical quartz crystal microbalance. A marked influence of hydrogen peroxide on the Cu(II), In(III) and Ga(III) electrochemical system is evidenced. Hydrogen peroxide enables the incorporation of indium and gallium as oxides/hydroxides at much less negative potentials than the In and Ga metals. A reaction path is proposed which accounts for the main experimental results. The reduction process starts with the reduction of cupric species, which is followed by the reduction of hydrogen peroxide. For peroxide concentrations higher than 20 mM, the precipitation of Ga and In oxides/hydroxides takes place. At more negative potentials the reactions become controlled by mass transfer allowing to control the composition of the films.

A Novel Core-Shell Structure of Anti-Reflection Layer for Cu(In,Ga)Se2 Solar Cell Application

Copper-indium-gallium- diselenide (CIGS) is one of the potential candidates for high conversion efficiency solar cells with direct band gap of 1~1.7 eV and high absorption coefficient of 104~105 cm-1. Introducing an anti-reflection layer on top of CIGS solar cell can enhance light scattering in the device, prolong optical path and therefore increase the photocurrent. Surface texture is one of the approaches to reduce the reflectance, and creating nanostructures by chemical etching or electrochemical method for anti-reflection layer has been reported. However, those approaches have concomitant disadva ntages including the complex mold fabrication and the etching solution remaining on the device. In this regard, we utilize glancing angle deposition system to fabricate mold-less self-synthesizing TiO2 helical nanostructure on the top of CIGS device as anti-reflection layer. In order to create gradient refractive index for further decreasing the reflectance, an oxide shell is deposited surrounding the TiO2 helical nanostructure by chemical bath deposition. The core-shell nanostructure is observed by transmission electron microscopy (TEM). According to UV-Vis spectroscopy, the reflectance is dropped after the nanostructure created on the device, which means that the CIGS layer can absorb more light and create more carriers. At last, the cell performance is improved due to the enhanced short circuit current (Jsc), which results from the decreasing reflectance. The basic research from this project will be beneficial to development in photovoltaic field both in research and industry fields.

A study on the optics of copper indium gallium (di)selenide (CIGS) solar cells with ultra-thin absorber layers

We present a systematic study of the effect of variation of the zinc oxide (ZnO) and copper indium gallium (di)selenide (CIGS) layer thickness on the absorption characteristics of CIGS solar cells using a simulation program based on finite element method (FEM). We show that the absorption in the CIGS layer does not decrease monotonically with its layer thickness due to interference effects. Ergo, high precision is required in the CIGS production process, especially when using ultra-thin absorber layers, to accurately realize the required thickness of the ZnO, cadmium sulfide (CdS) and CIGS layer. We show that patterning the ZnO window layer can strongly suppress these interference effects allowing a higher tolerance in the production process.

Fabrication of CIGS nanoparticle-ink using ball milling technology for applied in CIGS thin films solar cell

Abstract A copper–indium–gallium–diselenide layer was formed from the binary-alloy nanoparticles of In 2 Se 3 , Ga 2 Se 3 , and CuSe. Copper–indium–gallium–diselenide thin films were fabricated using the precursor nanoparticle-ink based on non-vacuum technology. The ink was fabricated by a ball milling procedure and the size of agglomerated copper–indium–gallium–diselenide powder after milling was less than 100 nm. Crystallographic, morphological, stoichiometric, and photovoltaic properties of the films were characterized by sintering the precursor copper–indium–gallium–diselenide samples with different holding times in a non-vacuum environment without selenization. Analytical results indicate that the copper–indium–gallium–diselenide absorption layer prepared with a holding time of 7.5 min has a chalcopyrite structure and favorable compositions. The obtained compositions of the sample are Cu 0.976 In 0.811 Ga 0.277 Se 1.935 , and the ratios of Ga/(In + Ga) and Cu/(In + Ga) are 0.254 and 0.896, respectively. The photovoltaic properties of this sample are E g of 1.185 eV, V oc of 0.643 V, N ds of 1.3 × 10 15 cm − 3 , and Ga of 0.277 mol, respectively.

High Efficiency Copper Indium Gallium DiSelenide (CIGS) by High Power Impulse Magnetron Sputtering (HIPIMS): A Promising and Scalable Application in Thin-film Photovoltaics

AbstractA novel method to deposit Copper Indium Gallium Diselenide (CIGS) using High Power Impulse Magnetron Sputtering (HIPIMS) was demonstrated and compared to the existing DC magnetron sputtering process. The metal-ion assisted thin-film growth inherent to a HIPIMS deposition process was used to advantage in depositing CIGS films. The HIPIMS plasma was characterized by measuring ion currents on a Langmuir probe placed into the plasma sufficiently close to the substrate. The high density plasma consisting of both metal and metal ions resulted in CIGS thin-film solar cells of superior conversion efficiencies (˜13%) as compared to conventional DC magnetron sputtering (˜10%). The efficiency enhancement was attributed to the improvement in the shunt resistance of the solar cell which corresponds to the increase in the density of the CIGS layer. Furthermore, it was also possible to grow large grained CIGS (˜1 micron) with high mobility metal-ions from the HIPIMS process. The scalability potential of the HIPIMS CIGS process was also demonstrated by running a 1.5 m long Copper-Indium-Gallium rotatable in a selenium environment using a HIPIMS power supply. The cylindrical magnetron was run at an average power of 7.8 KW and peak powers of as much as 300 KW with controlled arcing. The existence of a HIPIMS plasma was confirmed by the ion currents on the Langmuir probe and the metal signals from a Plasma Emission Monitor (PEM).

Structural properties of Cu(In,Ga)Se 2 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.

Copper indium gallium diselenide thin films for sun angle detectors in space applications

This work reports on processing, analysis and characterization of copper indium gallium diselenide (CIGS) used as a photosensitive layer for sensors such as sun angle detectors in space applications. CIGS-based solar cell devices with different CIGS layer thicknesses and the pn-junction located on the opposite side of the incidence of light were illuminated through their ultra-thin transparent molybdenum back contacts. The results from the current density versus voltage and quantum efficiency measurement indicate that the CIGS absorber layer may not exceed 750 nm at backside illumination, due to the limited CIGS diffusion length.

Development of p + , p, i, n, and n + -Type CuInGaSe2 Layers for Applications in Graded Bandgap Multilayer Thin-Film Solar Cells

Copper indium gallium diselenide layers with , p, i, n, and -type electrical conduction, as predetermined, have been electrodeposited from aqueous solutions in a single bath. The photoelectrochemical cell has been used as the key analytical tool to determine the electrical conduction type, and X-ray fluorescence has been used to determine the stoichiometry of the corresponding layers. Optical absorption, X-ray diffraction, and atomic force microscopy have been used to investigate the bandgap, bulk structure, and surface morphology of the material layers, respectively. It has been found that the bandgaps of these layers can be varied in the range . A four-layer n-n-i-p solar cell structure was fabricated and a corresponding energy band diagram for the device constructed. Current-voltage and capacitance-voltage measurements were carried out to assess the devices, and these parameters (, , and ) indicate encouraging characteristics enabling further development of multilayer thin-film solar cells based on . The addition of a layer to the structure improved device parameters as expected due to improvements at the metal contact to the surface of the n-n-i-p- structure.

Copper–indium–gallium–diselenide/molybdenum layers analyzed by corrected SIMS depth profiles

Polycrystalline copper–indium–gallium–diselenide (CIGS) may act as absorber material for solar radiation in thin film solar cells. CIGS layers are grown on molybdenum back contacts deposited on glass or flexible substrates. During the preparation process, substrate elements diffuse across the back contact into CIGS. We investigate the diffusion into the CIGS/Mo layers by SIMS depth profiling corrected with respect to recoil mixing and atomic mixing. Detaching the CIGS/Mo layers from the substrate allows profiling the layers from surface-side and backside. Thereby, the intermixing effects caused by the sputtering process may be separated. Comparing the surface-side with the mirrored backside depth profile enables us to correct the distortion by recoil mixing, which is anisotropic and different for each element. The remaining profile, now only distorted by atomic mixing (isotropic for all elements), is then corrected with respect to the Mo profile at the interface, which is known to exhibit a step function. Finally, the corrected depth profile allows the determination of diffusion coefficients of impurities in the complex multinary compound system.