Performance Of CIGS Solar Cells Research Articles

Designing novel plasmonic architectures for highly efficient CIGS solar cells

CIGS solar cells is one of the best thin film solar cells which have efficiency up to 22.6 %. In the recent decades, a lot of attention has been drawn to the methods of increasing solar cells efficiencies. One of the emerging technology for enhancing thin film solar cell efficiencies are using plasmonic effects in the visible or infrared part of the electromagnetic spectrum. Therefore, the primary goal of this study is to use plasmonic nanostructures in the active layer to enhance the absorption and consequently the efficiency of a thin film CIGS solar cell with a 1000 nm thickness. Different factors such as type of material, size and surface occupied with nanostructure can be effect on CIGS solar cell performance. In this research, the solar cell has been optically and electrically characterized in the presence of plasmonic nanostructure by simulations. The efficiency was determined by characteristics parameters such as absorption, quantum efficiency, electron-hole generation rate, current–voltage curve and power-voltage curve. Based on our simulations, the maximum efficiency of 25.61 % was achieved using gold nanocubic structures with dimensions of 100 nm, Occupied Factor of 0.16, positioned at the top of the active layer. This increase is due to increase in optical path of length of scattered light and consequently its absorption in the active layer. Moreover, enhancing carrier generation, decreasing recombination and improving carrier separation can be occurred due to localized surface plasmon resonance and the near-field distribution effect, which effectively scatter light into the active layer.

Effect of Defects at the Buffer Layer CdS/Absorber CIGS Interface on CIGS Solar Cell Performance

Effect of Defects at the Buffer Layer CdS/Absorber CIGS Interface on CIGS Solar Cell Performance

Influence of synthesis parameters of N-doped graphene quantum dots and polymer composite layer on the performance of CIGS solar cells

In this work, N-doped graphene quantum dots (N-GQDs) are used as luminescent downshifting layers, which enhanced the performance of the CIGS solar cells. For providing mechanical strength and chemical stability, a poly(methyl methacrylate) (PMMA) polymer-based matrix is used. However, the PMMA layer creates photoluminescence (PL) quenching, so N-GQDs/PMMA layer is annealed at various temperatures (20–80 °C) to obtain the best performance. These layers were applied on the top of the CIGS solar cells and the performance of the cell is evaluated. The best value of η is obtained for 60 °C. The Jsc and η values are enhanced to 36.03 mA/cm2 and 16.13% from 34.05 mA/cm2 and 14.70%, respectively. Furthermore, the PV cell parameters (photogenerated current density (Jph), shunt resistance (Rsh), series resistance (Rs), diode ideality factor (n), and reverse saturation current density (J0)) were also determined and analyzed to investigate the reduction in losses in the cell.

Efficiency enhancement of Cd-free buffer layers on CIGS solar cell performance using WxAMPS

In this paper, the impact of three buffers structures layers on the CIGS solar cell performance was numerically investigated using the one-dimensional simulation program wxAMPS. For Cd-free buffer layers, ZnS,µc_3C_SiC and Mg0.19Zn0.81O have been proposed as alternative buffers layers materials to replace the currently toxic CdS material used for the CIGS solar cells. A scrupulous optimization strategy based on the performance analysis of the thickness and doping concentration density effects was applied to each layer of the proposed stack solar cell structure ZnO/ Buffer layer/ CIGS. Moreover, the impact of the series resistance (Rs) was also examined and taken into account in the optimization process. As known, the combination of the parameter optimization (doping concentration density, thickness) with the lowest series resistance provides a minimum loss resistivity and high optical throughput. Consequently, the maximum achieved conversion efficiencies values for the three investigated solar cell structures (ZnS, µc_3C_SiC and Mg0.19Zn0.81O) were 31.16%,30.42% and 27.52%, respectively. The optimum value of 2µm was selected for the CIGS thickness while for the CIGS doping concentration density, the optimum values chosen were: 5×1018cm−3,3×1019cm−3 and 1×1018cm−3, respectively. These efficiencies parameters were obtained with a thickness absorber of 2μm, a buffer thickness layer of 40nm, and a ZnO window layer of 20nm.

Performance enhancement of CIGS solar cells using ITO as buffer layer

The purpose of this research is the reduction of parasitic absorption to improve the CIGS solar cell performance. Decreasing the traditional CdS buffer layer thickness is a reduction method for parasitic absorption which yields to a higher photocurrent. However, degradation of the open-circuit voltage (Voc) and fill factor (FF) are observed in J-V measurements as a thin (<30 nm) CdS buffer layer is applied. Moreover, the toxic CdS has a relatively low bandgap which tends to a significant parasitic absorption in the blue wavelength region. Here, Indium Tin Oxide (ITO) with a larger bandgap is suggested as an alternative buffer layer, which unlike the CdS, demonstrates a significant efficiency enhancement without adversely affecting Voc and FF. ITO is an environmentally friendly substance which its ultra-thin thickness leads to a significant short-circuit current (Jsc) enhancement. Hence, an improvement of efficiency about 6% is achieved by successfully replacing the traditional CdS layer with ITO layer in conventional CIGS solar cell. Furthermore, ZnMgO (ZMO) with more transparency and larger bandgap, was applied to replace conventional ZnO window layer of the CIGS solar cell for further increment in Jsc. In addition, ZMO as a proper window layer in the proposed cell structure tends to the modification of J–V curve distortion at low temperatures. Ultimately, the final proposed structure with the alternative window layer (Mo/CIGS/ITO/ZMO/AZO) exhibited 7.5% efficiency improvement in comparison with the conventional solar cells.

Improving the absorption spectrum and performance of CIGS solar cells by optimizing the stepped band gap profile of the multilayer absorber

In this paper, we investigate a way to improve the performance of thin films CIGS-based solar cells by optimizing their spectral responses. Band gap profile grading, aroused this last decade as a very promising strategy to achieve higher efficiency. This work was performed on a CIGS-based thin-film solar cell model, using cadmium sulphide CdS as a buffer layer, with zinc oxide ZnO as window layer. Focusing on electrical properties such as band gap and electron susceptibility, we modified gallium content of the absorber layer of a reference cell. Using aforementioned band gap grading strategy, we stacked three CIGS layers with different gallium contents, and we modelled a stepped band gap profile using SCAPS-1D. The comparative analysis of the results obtained through numerical simulation, with those of six different band gap profiles of the absorber layer, supports the statement that, stepped band gap profile is a promising approach for engineering improvement of high-efficiency CIGS-based solar cells. In fact, the absorption spectrum of the optimized cell has improved compared to the other band gap profiles simulated in this work; with a peak external quantum efficiency (EQE) of 94%. Efficiencies losses dues to recombination were reduced and the generated photocurrent is higher than that of classical profiles. Record efficiency of 28.03% was achieved with a fill factor of 86.42%. We believe absorber layer stacked in a stepped band gap profile, as a complementary approach to improve performances, is definitely a must-have technology for all future generations high efficiency thin films solar cells.

Numerical simulation of quantum dots as a buffer layer in CIGS solar cells: a comparative study

Quantum bandgap buffer layers can improve sunlight absorption in the short wavelength region, hence improving the performance of CIGS solar cells. In this study, we use numerical modelling to determine the impact of various buffer layers' electrical characteristics on the performance of CIGS thin film photovoltaic devices, particularly, carrier concentration and the quantum effect. As well Ag2S buffer layer has been experimentally examined to fulfilment its effect in term of bulk and quantum bandgap. Experimental results depicted that, Ag2S QDs has polycrystalline nature of films, with smooth surface roughness, and average diameter 4 nm. Meanwhile, a simulation revealed that the Fermi level of the (n-buffer layer) material shifts closer to the conduction band with an increase in carrier concentration. The findings indicate that, a buffer layer with a wider bandgap and carrier concentration is an essential demand for achieving a device with a higher conversion efficiency and a broader bandgap-CBO window. It was attributed to beneficial synergistic effects of high carrier concentration and narrower depletion region, which enable carriers to overcome high CBO barrier. Most importantly, modelling results indicate that the optic-electrical characteristics of the buffer layer are critical in determining the progress of a CIGS solar cell.

Above 15% Efficient Directly Sputtered CIGS Solar Cells Enabled by a Modified Back-Contact Interface.

The Schottky back-contact barrier at the Mo/Cu(In,Ga)Se2 (CIGS) interface is one of the critical issues that restrict the photovoltaic performance of CIGS solar cells. The formation of a MoSe2 intermediate layer can effectively reduce this back-contact barrier leading to efficient hole transport. However, the selenium-free atmosphere is unfavorable for the formation of the desired MoSe2 intermediate layer if the CIGS films are prepared by the commonly used direct sputtering process. In this work, high-efficiency CIGS solar cells with a MoSe2 intermediate layer were fabricated by the direct sputtering process without a selenium atmosphere. This is enabled by an intermediate CIGS layer deposited on the Mo substrate at room temperature before being ramped to a high temperature (600 °C). The room-temperature-deposited amorphous CIGS intermediate layer is Se rich, which reacts with the Mo substrate and forms very thin MoSe2 at the interface during the high-temperature process. The formed MoSe2 decreased the CIGS/Mo barrier height for better hole transport. Consequently, the CIGS solar cell with an 80 nm intermediate layer achieved a power conversion efficiency of up to 15.8%, which is a benchmark efficiency for the direct sputtering process without Se supply. This work provides the industry a new approach for commercialization of directly sputtered CIGS solar cells.

High-performance ultrathin Cu(In,Ga)Se2 solar cell optimized by silvaco tools

In this work, we investigated the influence of the cell pitch, opening width, Ga/(In + Ga) ratio, absorber layer thickness, and doping on ultrathin CIGS solar cell performance by using ATLAS tools. First, to validate our investigated solar cell, we discuss and compare our simulation models with fabricated cells with/without rear-passivation Al2O3/Cu(In1−xGax)Se2. We observed significant improvements in cell performance while using a thin film Al2O3 for the rear-passivation with a high density of negative charge, where the rear side contact recombination losses can then be reduced. The simulation results follow the experimental trends, highlighting the beneficial effects of rear-passivation in the ultrathin absorber layer. However, poor passivation was observed when a rear-passivation layer is with a high density of positive charge or in high contact resistance at Ag/CIGS interface. Consequently, the optimum combination led to achieving 14.30% with 1016 cm−3, 2.5 µm, and 250 nm for absorber doping, cell pitch, and cell width, respectively. The obtained results from the simulated cells were compared to the recently published research work.

Numerical Simulation of Copper Indium Gallium Diselenide Solar Cells Using One Dimensional SCAPS Software

The effect of multivalent defect density, thickness of absorber and buffer layer thickness on the performance of CIGS solar cells were investigated systematically. The study was carried out using Solar Cells Capacitance Simulator (SCAPS) code, which is capable of solving the basic semiconductor equations. Employing numerical modelling, a solar cell with the structure Al|ZnO : Al|In2S3|CIGS|Pt was simulated and in it, a double acceptor defect (-2/-1/0) with a density of 1014 cm-3 was set in the absorber in the first instance. This initial device gave a power conversion efficiency (PCE) of 25.85 %, short circuit current density (Jsc) of 37.9576 mAcm-2, Photovoltage (Voc) of 0.7992 V and fill factor (FF) of 85.22 %. When the density of multivalent defect (-2/-1/0) was varied between 1010 cm-3 and 1017 cm-3 the solar cells performance dropped from 26.81 % to 16.87 %. The champion device was with multivalent defect of 1010 cm-3 which shows an enhancement of 3.71 % from the pristine device. On varying the CIGS layer thickness from 0.4 um to 3.6 um, an increase in PCE was observed from 0.4 um to 1.2 um then the PCE began to decrease beyond a thickness of 1.2 um. The best PCE was recorded with thickness of 1.2 um which gave Jsc of 37.7506 mAcm-2, Voc of 0.8059 V, FF of 85.2655 %. On varying the In2S3 (buffer) layer thickness from 0.01 um to 0.08 um, we observed that there was no significant change in photovoltaic parameters of the solar cells as buffer layer thickness increased.

Numerical simulation of the effect of varied buffer layers on the performance of Cu(In, Ga)Se2 solar cells using Silvaco Tcad 2D

The CIGS thin-film solar cells Solar cells are regarded as one of the most promising photovoltaic technologies. They have the advantage of fast and low-cost manufacturing by depositing several thin layers. In this work, a numerical simulation was made to compare the effect of different buffer layers (CdS, ZnS, ZnSe, and In2S3) on the performance of CIGS solar cells using Silvaco Tcad 2D software. The results show that each buffer layer influences the performance of the cell. Therefore, our results suggest that the ZnS material as a buffer layers has better performance for our cell (Jsc=37.0252mAcm2, Voc=1,281, FF=88,01 , ƞ=20,88).

Simulation of Effects of Defects and Layers Thickness on the Performance of CIGS Solar Cells

Simulation of Effects of Defects and Layers Thickness on the Performance of CIGS Solar Cells

The role of metastability and concentration on the performance of CIGS solar cells under Low-Intensity-Low-Temperature conditions

Commercially available lightweight-flexible CIGS solar cells are investigated under the Low-Intensity-Low-Temperature (LILT) conditions that exist at Mars, Jupiter, and Saturn. Current density-voltage measurements, concentrated solar, and external quantum efficiency measurements are performed under varying temperatures and illumination intensities to determine the applicability and performance of flexible CIGS in outer planetary conditions. The well-known metastability of the CIGS absorber is observed as a result of a barrier to minority carrier extraction at the CIGS/CdS interface under higher intensity illumination. However, despite the low temperatures and low intensities experienced in deeper space, the presence of this barrier does not significantly affect the performance of the solar cells under LILT conditions. This is attributed to the lower photogeneration rate of carriers particularly at conditions relative to Saturn and Jupiter, which appears to be less than the thermionic emission rate across the barrier and therefore the carrier extraction is relatively unaffected under these illumination conditions. At elevated temperatures and/or intensities such as at AM0 and conditions relative to Mars, however, the higher carrier generation rate results in the appearance of large series resistance and a significant loss of fill factor at irradiation levels greater than 1-sun AM0. Proton irradiation of the solar cells systematically reduces the performance, predominately through the formation of defect states in the absorber layer, the presence of which is increasingly more prohibitive in LILT conditions due to the low thermal energy of the minority carriers and the subsequent increased effect of SRH recombination.

Numerical analysis of CdS-CIGS interface configuration on the performances of Cu(In,Ga)Se2 solar cells

One dimension solar Cell Simulation package (SCAPS) is used to analyze the impact of the CdS-CIGS interface configuration on the performances of CIGS solar cells. We simulated the current-voltage characteristic of two models of the cell: one with a donor type defect (OVC model) and the other with acceptor type defect (P+ model) at the CdS-CIGS interface. The advantages and disadvantages of these CIGS surface configuration on the electrical parameters were discussed according to their thicknesses, defect density and carrier lifetime. The simulation results show that the model with the P+ layer has poor performance when its thickness and defect density increase, due to a huge distortion on the J-V characteristic. On the other hand, the OVC layer plays a fundamental role in the performance of CIGS solar cells. Better performances are obtained with the OVC model when the density of donor defect is in the range 1013 - 1015 cm−3, the charge carriers lifetime in the range 0.02 - 1 ns, and the thickness of the OVC layer in the range 200 - 400 nm.

Cd-free Cu(InGa)Se2 solar cells with eco-friendly a-Si buffer layers

CdS, In2S3 and ZnO-based materials are typically adopted as buffer layers in high efficiency CIGS solar cells. However, the drawbacks involved toxicity, complicated synthesis process and environmental damage of aforementioned materials would someday limit the development themselves. Here, for the first time, eco-friendly and low-cost a-Si thin films prepared by e-beam evaporation were used as buffer layers in CIGS solar cells. Thickness of a-Si films was changed to optimize the performance of CIGS solar cells through investigating their optical, structural and electrical properties. It revealed that the conduction band alignment of CIGS and a-Si is a favorable spike and a 60 nm a-Si film is optimal for CIGS/a-Si interface properties. Following the SCAPS simulation, bandgaps and conduction band energy level of CIGS films were facilely modulated through altering the Ga/(Ga + In) ratios. The conversion efficiency of solar cell with modified CIGS film was relatively improved by over 30% compared to the pristine one. The present work provides a new and eco-friendly strategy for fabrication of CIGS solar cells and expands the application of a-Si thin films as buffer layers for solar cells.

Boosting Electrical Performance of CIGS Solar Cells: Buffer Layer Effect

Boosting Electrical Performance of CIGS Solar Cells: Buffer Layer Effect

Quantitative Analysis and Band Gap Determination for CIGS Absorber Layers Using Surface Techniques.

Recently, Cu(InXGa(1−X))Se2 (CIGS) absorber layers have been extensively studied by many research groups for thin-film solar cell technology. CIGS material is particularly promising due to its exceptionally high absorption coefficient and large band gap range, which is adjustable as a function of alloy stoichiometry. To enhance the conversion performance of CIGS solar cells, understanding the CIGS structure and composition is a crucial challenge. We conducted a quantitative study to determine the bulk composition of the major elements such as Cu, In, Ga, and Se of four different CIGS photovoltaic cells. The compositional information was obtained by X-ray fluorescence (XRF), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICP-MS). Then, the XRF concentration ratio was compared with the intensity ratio of fs-LA-ICP-MS to investigate the potential of accurate and rapid analysis using the fs-LA-ICP-MS technique. In contrast to the bulk information, the surface techniques can supply detailed information about the chemical composition across the depth profile. Here, elemental depth distributions of CIGS thin films were investigated using magnetic sector secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy (AES). The atomic distributions of four different CIGS absorber layers exhibited a good agreement although they were obtained using two different surface instruments, AES and SIMS. Comparative analysis results of different CIGS absorber layers using SIMS, AES, and fs-LA-ICP-MS provide us with the appropriate technique for the information of accurate composition in a rapid analysis time. Thanks to a simple approach using the Ga/(In + Ga) ratio, the optical band gap energy of the Cu(InXGa(1−X))Se2 quaternary layer was monitored in the entire CIGS layer. The elemental distribution and the band gap determination were then used to elucidate their relationship to the corresponding CIGS cell efficiency result.

Addressing the impact of rear surface passivation mechanisms on ultra-thin Cu(In,Ga)Se2 solar cell performances using SCAPS 1-D model

We present a (1-D) SCAPS device model to address the following: (i) the surface passivation mechanisms (i.e. field-effect and chemical), (ii) their impact on the CIGS solar cell performance for varying CIGS absorber thickness, (iii) the importance of fixed charge type (+/−) and densities of fixed and interface trap charges, and (iv) the reasons for discrete gains in the experimental cell efficiencies (previously reported) for varying CIGS absorber thickness. First, to obtain a reliable device model, the proposed set of parameters is validated for both field-effect (due to fixed charges) and chemical passivation (due to interface traps) using a simple M-I-S test structure and experimentally extracted values (previously reported) into the SCAPS simulator. Next, we provide figures of merits without any significant loss in the solar cell performances for minimum net −Qf and maximum acceptable limit for Dit, found to be ∼5×1012cm−2 and ∼1×1013cm−2eV−1 respectively. We next show that the influence of negative fixed charges in the rear passivation layer (i.e. field-effect passivation) is more predominant than that of the positive fixed charges (i.e. counter-field effect) especially while considering ultra-thin (<0.5μm) absorber layers. Furthermore, we show the importance of rear reflectance on the short-circuit photocurrent densities while scaling down the CIGS absorber layers below 0.5μm under interface chemical and field-effect passivation mechanisms. Finally, we provide the optimal rear passivation layer parameters for efficiencies greater than 20% with ultra-thin CIGS absorber thickness (<0.5μm). Based on these simulation results, we confirm that a negatively charged rear surface passivation with nano-point contact approach is efficient for the enhancement of cell performances, especially while scaling down the absorber thickness below 0.5μm.

Effect of the deposition process of window layers on the performance of CIGS solar cells

Abstract The effects of the formation process of transparent conducting electrodes on the performance of Cu(In,Ga)Se2 thin film solar cells were examined. B:ZnO and (Ga,Al):ZnO thin films deposited using metalorganic chemical vapor deposition (MOCVD) and magnetron sputtering, respectively, were compared in terms of the unit thin films and solar cell device performance. Both unit films formed under optimized process conditions showed similar electrical resistance, whereas the optical reflectance of B:ZnO by MOCVD was superior to that of the sputtered film. In the case of the B:ZnO film deposited on the absorber layer, the surface roughness became greater than the unit film on the test glass. The short-circuit current of the solar cell fabricated with B:ZnO was 3% higher than that with (Ga,Al):ZnO due to the enhanced light scattering. The junction quality and defect chemistry were identical in both devices, which suggests that there was no plasma damage due to sputtering.

Selenium Flux Effect on Cu(In,Ga)Se2 Thin Films Grown by a 3‐stage Co‐evaporation Process

AbstractAn investigation into the effects of Se flux on absorber thin film growth at each step of a 3‐stage co‐evaporation process was conducted to further optimize the performance of CIGS solar cells. In ‘step I’ forming an In‐Ga‐Se precursor thin film during the 3‐stage process, Se flux affected the preferred orientation of the CIGS crystal structure, but not the film morphology. In ‘step II’, no correlation was found between Se flux and the crystal structure, although excessively high Se flux employed throughout the 3‐stage process degraded the solar cell performance. A CIGS thin film, with a (220/204) crystal orientation, minor physical surface defects and ∼20 nm thick MoSe2 at CIGS/Mo interface, was obtained by fine control of Se flux conditions (high Se flux at ‘step I’ and low Se flux at ‘step II’) at optimum substrate temperatures. The solar cell fabricated using the aforementioned CIGS thin film showed the highest conversion efficiency of 20.02 %.