Silicon Photovoltaic Cells Research Articles

Intelligent Classification of Silicon Photovoltaic Cell Defects Based on Eddy Current Thermography and Convolution Neural Network

In this article, defects in the production process of silicon photovoltaic (Si-PV) cells are urgently needed to be detected due to their serious impact on the normal generation of PV system. In view of the shortcomings, such as low-defect efficiency, few detection data, and high detection error rate in the existing industrial production line, the main research purpose of this article is to complete an intelligent classification method for efficient and innovative defect detection for Si-PV cells and modules. The purpose is to improve the detection efficiency of Si-PV cell, to ensure the safety and reliability of Si-PV cell production process, to achieve large number of Si-PV cell defects detection and classification. First, the eddy current thermography system of Si-PV cells is established. Second, principal component analysis, independent component analysis, and nonnegative matrix factorization algorithms are compared for thermography sequences processing. Third, LeNet-5, VGG-16, and GoogleNet models are compared for Si-PV cell defects classification. Finally, the results show that the proposed method have successful application in Si-PV cell defects detection and classification.

Experimental study on slicing photovoltaic polycrystalline silicon with diamond wire saw

At present, polycrystalline silicon photovoltaic cells play a dominant role in silicon-based solar cells because of its advantages such as relatively simple preparation process and relatively low cost. Slicing is the first mechanical processing procedure for battery cells, the quality of sawn surface affects the cost of subsequent processes such as texture making, also affects the breaking strength of battery cells and the photoelectric conversion efficiency and other performances. In this paper, polycrystalline silicon sawing experiments are carried out, and the effects of main process parameters, such as the workpiece feed speed, the wire moving speed, the ratio of the workpiece feed speed to the wire moving speed, and the sawn workpiece size, on the surface morphology and roughness Ra of the photovoltaic polycrystalline silicon slice are analyzed. Orthogonal experimental method was used to analyze the primary and secondary order and positive and negative effects of various factors on surface morphology and surface roughness, the optimum process parameters were obtained, and the wear morphology and mechanism of wire were analyzed. The research results show that: within the range of process parameters studied in this paper, the surface morphology of polycrystalline silicon slices shows a comprehensive effect of material ductility and brittleness removal. Reducing the workpiece feed speed and size, increasing the wire moving speed will increase the proportion of the ductile smooth area on the slice surface and decrease the surface roughness Ra value, the slice surface roughness Ra value is basically unchanged when workpiece feed speed and wire speed change at the same time but the ratio of them remains constant. Compared with the wire moving speed and the workpiece size, the workpiece feed speed has the greatest influence on the surface morphology and roughness. Abrasive falling off and coating wear are the main wear forms of the wire.

Temperature dependence of potential-induced degraded p-type mono-crystalline silicon photovoltaic cell characteristics

In this paper, the temperature dependence of the characteristic parameters for a p-type mono-crystalline silicon photovoltaic cell before and after a potential-induced degradation (PID) stress, is measured and compared. It is demonstrated that a 9 h PID stress causes both a drastic decrease in the value of shunt resistance by ∼35 times and a decrease in the open-circuit voltage, Voc by ∼34%. Consequently the maximum power density, Pmax is decreased by ∼62%. The temperature coefficient (TC) of Pmax increases from −0.459 to −0.330 caused by a 0 to 3 h PID stress and then decreases to −0.471%/°C caused by a 3 to 9 h PID stress. Before PID stress, the TC of Pmax was determined mainly by the TC of Voc. However, after PID stress, the TC of Pmax was determined both by the TCs of Voc as well as by the fill factor.

Stress mitigation for adhesively bonded photovoltaics with fibre reinforced polymer composites in load carrying applications

Structural loads, especially in-plane compression, may cause local buckling and debonding of the photovoltaic (PV) cells that are mechanically integrated with structural members and this may lead to degradation in their electrical performance. This paper proposes an approach to mitigate the strains transferred from structural members to PV cells through the partial composite action provided by low-modulus adhesives. Specimens were fabricated by bonding amorphous silicon (a-Si) PV cells to glass fibre reinforced polymer (GFRP) structural components by an adhesive layer of 0.5- or 2.0-mm thickness. Two types of adhesives were used including a two-part rigid epoxy adhesive and a low-modulus silicone adhesive. These integrations were then submitted to in-plane compressive loadings. PV cells bonded by the silicone adhesive showed no damages during loading. While for PV cells bonded by epoxy adhesives, obvious electrical performance degradations were observed, when the strain reached 0.62% or 0.23% for specimens bonded by epoxy with a layer thickness of 0.5 mm or 2.0 mm respectively. Debonding and local-buckling of the PV cells were also witnessed. Theoretical analysis was conducted to understand the strain mitigation of the adhesive as a result of the induced partial composite action. Results demonstrate that such strain differences between the GFRP and the bonded PV cell are dominated by the shear modulus and thickness of the adhesive layer as well as elastic modulus, thickness and length of the PV cell. The theoretical analysis was validated by finite element (FE) modelling and design suggestions are provided accordingly.

Boron–Oxygen Complex Responsible for Light‐Induced Degradation in Silicon Photovoltaic Cells: A New Insight into the Problem

Results available in the literature on minority carrier trapping and light‐induced degradation (LID) effects in silicon materials containing boron and oxygen atoms are briefly reviewed. Special attention is paid to the phenomena associated with “deep” electron traps (J. A. Hornbeck and J. R. Haynes, Phys. Rev. 1955, 97, 311) and the recently reported results that have linked LID with the transformation of a defect consisting of a substitutional boron atom and an oxygen dimer (BsO2) from a configuration with a deep donor state into a recombination active configuration associated with a shallow acceptor state (M. Vaqueiro‐Contreras et al., J. Appl. Phys. 2019, 125, 185704). It is shown that the BsO2 complex is a defect with negative‐U properties, and it is responsible for minority carrier trapping and persistent photoconductivity in nondegraded Si:B+O samples and solar cells. It is argued that the “deep” electron traps observed by Hornbeck and Haynes are the precursors of the “slow” forming shallow acceptor defects, which are responsible for the dominant LID in boron‐doped Czochralski silicon (Cz‐Si) crystals. Both the deep and shallow defects are BsO2 complexes, transformations between charge states and atomic configurations of which account for the observed electron trapping and LID phenomena.

Assessment of an early degraded PV generator

The detection and the analysis of in field early degradation of a grid connected photovoltaic system located at the Institute of Energy and Environment of the University of São Paulo (IEE-USP) are presented. The PV generator is composed by 260 W photovoltaic (PV) modules made of N-type monocrystalline silicon PV cells. Loss of generation capability during the second year of operation was revealed by the PV system’s SCADA. Subsequent measurements showed similarities with strong ageing degradation mechanisms and Potential Induced Degradation (PID) was also detected.

< 50-μm thin crystalline silicon heterojunction solar cells with dopant-free carrier-selective contacts

Dopant-free carrier-selective contacts are emerging in the field of crystalline silicon (c-Si) photovoltaic solar cells, which are potential to further improve the power conversion efficiency (PCE) and lower the cost of c-Si solar cells. Here, we demonstrate tens of microns thin c-Si heterojunction solar cells with substochiometric MoOx and LiFx as dopant-free hole- and electron-selective contacts, respectively. Chemical thinning of 200-μm thick c-Si wafers enables the production of proof of concept devices with good flexibility and strong performance. When the wafer thickness is reduced to 49.4 μm (24.7% of the initial thickness), the power conversion efficiency (PCE) of the solar cell still maintains 88.2% of the initial value for the 200-μm thick cell. When the wafer thickness becomes less than 10% (or even 3.4%) of the initial value, 61.2% and 39.2% of the initial PCEs are still achieved for the 14.8- and 6.8-μm thick cells, respectively. Passivating and carrier-selective effects of the MoOx and LiFx films allow for the maintenance of performance. An oxide interlayer at the MoOx/c-Si interface passivates the dangling bonds of the c-Si surface and improves the minority carrier lifetime. Field-effect passivation and carrier-selective effects induced by the band bending near the MoOx/c-Si interface and the Al/LiFx/c-Si interface play an important role in maintaining high open-circuit voltage and high fill factor. To the best of our knowledge, this is the first time that <100-μm thin c-Si heterojunction solar cells are reported with undoped contacts. Our solar cells have been fabricated on thin c-Si wafers with low-temperature processes and without additional doping, and thus our work provides a promising cost-effective means in the field of thin and flexible c-Si solar cells.

Indoor experiments of dust deposition reduction on solar cell covering glass by transparent super-hydrophobic coating with different tilt angles

Dust deposition on solar photovoltaic (PV) panels would greatly reduce the PV output efficiency, especially in dusty regions. This paper investigated dust deposition reduction on solar cell covering glass by transparent super-hydrophobic coating under different PV tilted angles. The macroscopic and microscopic dust deposition patterns, dust deposition density, spectral transmittance of covering glass and PV efficiency reduction caused by dust deposition were studied and analyzed. The results showed that dust deposition on the glass surface can be greatly reduced by super-hydrophobic coating due to the low adhesion energy. The super-hydrophobic coating has a better performance on dust deposition reduction compared with hydrophobic coating. The deposition density on the glass with super-hydrophobic coating is just 44.4%, 28.6% or 11.2% of the bare surface for tilt angle θ = 30°, θ = 45° or 60°, respectively. The spectral transmittance of coated glass and the PV efficiency are obviously higher compared with bare glass case after dust deposition. Moreover, the self-cleaning coating has better performance for large tilt angle and poly-crystalline silicon PV cell. The performance of super-hydrophobic coating on dust deposition reduction is similar between the test dust and the real dust obtained from Guangzhou, China.

Corrections to “Corrosion-Induced AC Impedance Elevation in Front Electrodes of Crystalline Silicon Photovoltaic Cells Within Field-Aged Photovoltaic Modules” [May 19 741-751

Presents corrections to author information in the paper, “Corrosion induced AC impedance elevation in front electrodes of crystalline silicon photovoltaic cells within field-aged photovoltaic modules,” (Tanahashi, T., et al), IEEE J. Photovolt., vol. 9 no. 3, pp. 741–751, May 2019.

Electromagnetic Induction Heating and Image Fusion of Silicon Photovoltaic Cell Electrothermography and Electroluminescence

In the process of research, development, production, service, and maintenance of silicon photovoltaic (Si-PV) cells and the requirements for detection technology are becoming more and more important. This paper aims to investigate electromagnetic induction (EMI) and image fusion to improve the detection effect of electrothermography (ET) and electroluminescence (EL) of multidefects in Si-PV cells. First, the principles of ET, EL, and other physical processes including EMI, thermal radiation, and luminescence radiation are analyzed in this paper. ET and EL techniques after EMI improvement are used to detect different defects including scratch, broken gridline, surface impurity, hidden crack, and so on. The qualitative results show that EMI can greatly improve the defect detection ability of ET and EL. Then, an image-fusion rule based on L1 norm is proposed to fuse the sparse vector of the ET and EL images. The integration and complementarity of the two wavelength detection data are achieved. Finally, the image-fusion results of sparse representation (SR) algorithm is compared with discrete wavelet transform, curvelet transform, dual-tree complex wavelet transforms, and nonsubsampled contourlet transform. Five objective evaluation indexes including root mean square error, peak signal-to-noise ratio, correlation coefficient, mutual information, and structural similarity index are used to evaluate the fusion results. Overall evaluation results show that the SR algorithm is superior to the other algorithms.

Identification of the mechanism responsible for the boron oxygen light induced degradation in silicon photovoltaic cells

Silicon solar cells containing boron and oxygen are one of the most rapidly growing forms of electricity generation. However, they suffer from significant degradation during the initial stages of use. This problem has been studied for 40 years resulting in over 250 research publications. Despite this, there is no consensus regarding the microscopic nature of the defect reactions responsible. In this paper, we present compelling evidence of the mechanism of degradation. We observe, using deep level transient spectroscopy and photoluminescence, under the action of light or injected carriers, the conversion of a deep boron-di-oxygen-related donor state into a shallow acceptor which correlates with the change in the lifetime of minority carriers in the silicon. Using ab initio modeling, we propose structures of the BsO2 defect which match the experimental findings. We put forward the hypothesis that the dominant recombination process associated with the degradation is trap-assisted Auger recombination. This assignment is supported by the observation of above bandgap luminescence due to hot carriers resulting from the Auger process.

Outdoor performance evaluation of a holographic solar concentrator optimized for building integration

A holographic solar concentrating system with a Silicon photovoltaic (PV) cell is designed, constructed and characterized. The design is based on a previous system and is further optimized. The cylindrical holographic lenses forming the concentrating system are modeled with a ray-tracing algorithm based on Coupled Wave Theory and are recorded on Bayfol® HX photopolymer. Measurements are carried out outdoors with solar illumination and provide a current density of 146 mA/cm2 with a current concentration factor of 3.48, validating the theoretical simulations results (172 mA/cm2 and 3.81, respectively). The effect of the temperature on the performance of the Holographic Optical Elements (HOEs) is studied and taking it into account by assuming a 1.3° tilt of the fringes of the hologram caused by thermal expansion (which is reversible if the HOEs are encapsulated and sealed) provides simulation results closer to the experimental ones (a current density value of 155 mA/cm2 and current concentration of 3.43). The ageing of HOEs recorded in Bayfol® HX photopolymer due to the outdoor environmental conditions is also analyzed, revealing the need of encapsulation and sealing.

Role of Nanostructured Photoanode and Counter Electrode on Efficiency Enhancement of DSSCs

In recent years, dye-sensitized solar cells (DSSCs) have received widespread attention due to their low cost compared to conventional silicon photovoltaic cells. However, to reach optimal device efficiencies, much work is still required. Nanotechnology opens a door to creating various nanostructures and tailing materials for use in DSSCs. Here we reviewed the development in nanomaterials based on modified electrodes which utilize the advantages of high electrocatalytic ability and high surface area due to their nanostructured morphology. This review highlights recent developments in DSSCs and their key components with respect to nanostructured modification, which will provide deep insights and guidance for researchers to design and develop cost-effective and efficient DSSCs.

Continuous performance assessment of thin-film flexible photovoltaic cells under mechanical loading for building integration

Building integration using thin-film flexible photovoltaic (PV) cells with load-carrying structures requires understanding of their electrical performance under continuous mechanical loadings. Limited results mainly focus on the electrical performance of PV cells under certain fixed mechanical strains. In this paper, an approach is examined to continuously apply tensile strains on PV cell specimens; therefore the short circuit current (ISC) and open circuit voltage (VOC) are constantly monitored. Two types of PV cells are studied under the proposed approach including amorphous silicon (a-Si) and organic PV cells and the results demonstrate its practicability to determine the critical tensile strains reliably for both PV types. It is found that VOC is more sensitive than ISC to the applied tensile strain for both types of PV cells and substantial degradation in VOC for a-Si cells initiates at the tensile strain of 1.51%. For organic cells, significant reduction in VOC is observed at the critical tensile strain of 1.46% in association with yielding of the substrate. While noticeable degradation can be only observed in ISC from 1.67% strain for a-Si PV cells and from 3.09% strain for organic ones. In addition, linear declines with temperature in VOC of both PV types are quantified for temperatures over 30 °C.

Tunable thermal and electricity generation enabled by spectrally selective absorption nanoparticles for photovoltaic/thermal applications

High-efficiency photovoltaic/thermal systems are being put forward to develop a low-carbon economy. Moreover, nanofluid-based beam splitters with excellent property of selective spectrum absorption have shown great potential to enable effective running of the solar cells and thermal collectors without any interference. In this work, a mathematic model to evaluate the performance of the nanofluid-based beam splitter was established. Ag@TiO2 nanoparticles with selective absorption capability were suspended in water to generate high-efficiency beam splitters for photovoltaic/thermal applications. The nanoparticles exhibited high absorptivity in the visible light wavelengths and good transmittance in the spectral response range of silicon photovoltaic cell. Under the assumption that the relative worth factor was equal to 3, the 200 ppm nanofluid produced ~1.4 times of the overall efficiency compared to water. Furthermore, the merit function reached 2.16 when 100 ppm nanoparticles were suspended owing to high photothermal conversion efficiency of the Ag@TiO2 nanofluid. Moreover, tunable nanoparticle concentrations were adopted to obtain high-efficiency solar energy utilization. Such being the case, differential distributions between electric and thermal energy demands can be realized to match the variable requirements of electricity and heat across geographical differences.

Efficient Electrocatalytic Oxygen Evolution at Extremely High Current Density over 3D Ultrasmall Zero‐Valent Iron‐Coupled Nickel Sulfide Nanosheets

AbstractNonprecious water oxidation electrocatalysts that perform well at high current densities are among the key enabling drivers of renewable energy technologies. Herein, we report a novel strategy to produce 3D ultrasmall zero‐valent iron‐coupled nickel sulfides nanosheets (Fe0−NixSy) hybrid on self‐supported conductive Ni foam (denoted as Fe0−NixSy/NF) through a robust single‐step gas–solid reaction. In this 3D hybrid, the Fe0−NixSy nanosheets with a length of approximately 400 nm and an average thickness of 33 nm are uniformly grown on the Ni foam. Benefiting from the unique 3D hierarchical structure and synergistic effect between Fe0 and NixSy, the 3D Fe0−NixSy/NF hybrid shows an excellent electrocatalytic activity towards oxygen evolution reaction (OER) at extremely high current densities in basic media. The current densities of 1000 and 1500 mA cm−2 are achieved at low potentials of 1.57 and 1.60 V, respectively, thus meeting the expected OER standards for industrial applications. These overpotentials of the 3D Fe0−NixSy/NF hybrid are the lowest among all previously reported nickel‐sulfide‐based electrocatalysts, and are even superior compared to state‐of‐the‐art Ir/C catalysts. We further demonstrate that the integration of the 3D Fe0−NixSy/NF electrocatalyst as both anode and cathode with a silicon photovoltaic cell enables highly active and sustainable solar‐driven overall water splitting.

Photo‐Thermo‐Refractive Glasses Doped with Silver Molecular Clusters as Luminescence Downshifting Material for Photovoltaic Applications

AbstractSilver nanostructures, including molecular clusters and plasmonic nanoparticles, attract much attention due to their unique optical properties and potential applications in various fields. Glasses doped with silver molecular clusters are known to possess bright luminescence under UV excitation, which opens up prospects of using the glasses as solar spectral converters to overcome poor spectral response for most of photovoltaic cells in the short‐wavelength region. In this study, silver molecular clusters are formed in photo‐thermo‐refractive glass matrix both by UV irradiation and by Na+↔Ag+ion exchange and optically characterized. Photo‐thermo‐refractive glasses doped with silver molecular clusters, independently on silver introduction method, are shown to demonstrate broad absorption in the UV, intense white emission under excitation at 360 nm, and high photoluminescence quantum yield that meet requirements for luminescence downshifting materials. Despite this, only photo‐thermo‐refractive glass with silver molecular clusters uniformly distributed in the glass volume enhances the output power of a silicon photovoltaic cell, thus showing the potential for future application of photo‐thermo‐refractive glasses in photovoltaics, particularly in case of further experiments.

Temperature dependence of the short circuit current and spectral responsivity of various kinds of crystalline silicon photovoltaic devices

The short-circuit current Isc and spectral responsivity (SR) of crystalline silicon (c-Si) photovoltaic (PV) modules and cells are investigated at various device temperatures. The long-wavelength tail of SR shifts toward longer wavelengths as the temperature increases. Although the wavelength shift Δλ per temperature difference ΔT is dependent on the device structure and λ, the present results show that the shift in the quantum efficiency (QE), which is related to SR by QE ≈ SR × 1240/λ, can be approximated using the wavelength-independent constant of Δλ/ΔT ∼ 0.45 nm/K for various types of c-Si device. The results indicate that the temperature dependence of SR can be approximated using a simple relation for various types of c-Si PV device, which greatly improves the precision of spectral mismatch correction when SR at only one temperature is available.

Crystalline silicon photovoltaic cells used for power transmission from solar-pumped lasers: III. Prototype for proof of the light trapping concept

We have proven the light trapping concept for crystalline silicon (c-Si) photovoltaic (PV) cells used for power transmission from solar-pumped lasers (SPLs) emitting at 1064 nm. We fabricated a prototype of the PV cells in which four unique features were employed: (i) a 45-µm-thick c-Si wafer and an aperture of 100 µm diameter, (ii) a bandpass filter on the front surface and a diffuse reflector on the rear surface, (iii) a p+/p/n+ configuration illuminated from the p+-layer, and (iv) an Al/Ag double-layered electrode on the p+-front layer and a Ag electrode on the n+-rear layer for compatibility of ohmic contacts and high reflectance. Under 1064 nm laser illumination at 4.8 W/cm2, the external quantum efficiency was as high as 0.92 despite the use of a thin c-Si wafer, resulting in a conversion efficiency of around 35%. No marked detrimental effect was observed under more intense illumination up to 21.3 W/cm2.

Crystalline silicon photovoltaic cells used for power transmission from solar-pumped lasers: I. Light trapping concepts

We have proposed a light trapping concept for crystalline silicon photovoltaic (PV) cells used for power transmission from solar-pumped lasers (SPLs) emitting at 1064 nm. The underlying mechanism is multiple reflection between a multilayered angle-selective filter on the front surface and a diffuse reflector on the rear surface of the cell. For the stationary use and optical fiber connection of the SPL-PV combination in which the incident angles of the laser light to the PV cells (ϕ) change within 5–10°, double-cavity bandpass filters realize the required angle selection function. When the SPLs illuminate moving electric vehicles equipped with the PV cells at larger ϕ values, shortpass filters are appropriate. These specially designed angle-selective filters provide significant light trapping performance and consequently absorbances higher than the Yablonovitch limit up to ϕ = 45°. The fact that the present light trapping configuration requires no microfabrication processes is also a great advantage over two- and three-dimensional photonic crystal structures.