Multicrystalline Solar Cells Research Articles

Production of upgraded metallurgical-grade silicon for a low-cost, high-efficiency, and reliable PV technology

Upgraded metallurgical-grade silicon (UMG-Si) has the potential to reduce the cost of photovoltaic (PV) technology and improve its environmental profile. In this contribution, we summarize the extensive work made in the research and development of UMG technology for PV, which has led to the demonstration of UMG-Si as a competitive alternative to polysilicon for the production of high-efficiency multicrystalline solar cells and modules. The tailoring of the processing steps along the complete Ferrosolar’s UMG-Si manufacturing value chain is addressed, commencing with the purification stage that results in a moderately compensated material due to the presence of phosphorous and boron. Gallium is added as a dopant at the crystallization stage to obtain a uniform resistivity profile of ∼1 Ω cm along the ingot height. Defect engineering techniques based on phosphorus diffusion gettering are optimized to improve the bulk electronic quality of UMG-Si wafers. Black silicon texturing, compatible with subsequent gettering and surface passivation, is successfully implemented. Industrial-type aluminum back surface field (Al-BSF) and passivated emitter and rear cell (PERC) solar cells are fabricated, achieving cell efficiencies in the range of those obtained with conventional polysilicon substrates. TOPCon solar cell processing key steps are also tested to further evaluate the potential of the material in advanced device architectures beyond the PERC. Degradation mechanisms related to light exposure and operation temperature are shown to be insignificant in UMG PERC solar cells when a regeneration step is implemented, and PV modules with several years of outdoor operation demonstrated similar performance to reference ones based on poly-Si. Life cycle analysis (LCA) is carried out to evaluate the environmental impact of UMG-based PV technology when compared to poly-Si-based technology, considering different scenarios for both the manufacturing sites and the PV installations.

Light Induced Degradation Quantification by Monitoring the VOC Output of Silicon Solar Cell Using Low-Cost Real-Time Virtual Instrumentation

Silicon-based solar cells suffer from different types of light-induced efficiency losses (can cause up to 10% loss), known as light-induced degradation (LID). Impurities, such as boron, iron, and oxygen, are common at different concentrations in these solar cells. They form active recombination defects in boron-doped mono-crystalline (Cz-Si) and multi-crystalline (mc-Si) solar cells during illumination. For the solar industry, this will lead to serious financial loss, hence the importance of inspecting and controlling the LID level accurately. Seeking to minimize the human factor and the inaccuracy that comes with it, we have proposed in this research a low-cost virtual instrumentation solution to provide a new real-time instrumentation technique for solar cell characteristics such as open circuit voltage (VOC). The virtual data acquisition system (VDAS) design is based on a low-cost Arduino board associated with MATLAB/Simulink software. Moreover, this system can collect in real time the values of solar cell outputs under prolonged illumination and under different temperatures of the LID test. Further, kinetic modeling of the solar cell output VOC variation as a function of light soak duration; shows the predominance of one type metastable defect over the LID test of c-Si solar cells. Additionally, degradation mechanism in mc-Si solar cells involve more than one metastable defect and are more complexes due to the mc-Si substrate elaboration technique compared to c-Si substrate. Furthermore, the temperature dependence of the concentrations (NVoc) and the thermal activation energies of the defects have been extracted from the experimental VOC measurements obtained using the VDAS. Finally, the system minimizes the test period and errors for solar cell characterization compared to traditional approaches.

Recent Progress of Film Fabrication Process for Carbon-Based All-Inorganic Perovskite Solar Cells

Although the certified power conversion efficiency of organic-inorganic perovskite solar cells (PSCs) has reached 25.7%, their thermal and long-term stability is a major challenge due to volatile organic components. This problem has been a major obstacle to their large-scale commercialization. In the last few years, carbon-based all-inorganic perovskite solar cells (C−IPSCs) have exhibited high stability and low-cost advantages by adopting the all-inorganic component with cesium lead halide (CsPbI3−xBrx, x = 0 ~ 3) and eliminating the hole-transporting layer by using cheap carbon paste as the back electrode. So far, many astonishing developments have been achieved in the field of C−IPSCs. In particular, the unencapsulated CsPbBr3 C-IPSCs exhibit excellent stability over thousands of hours in an ambient environment. In addition, the power conversion efficiencies of CsPbI3 and CsPbI2Br C-IPSCs have exceeded 15%, which is close to that of commercial multicrystalline solar cells. Obtaining high-quality cesium lead halide-based perovskite films is the most important aspect in the preparation of high-performance C-IPSCs. In this review, the main challenges in the high-quality film fabrication process for high performance C-IPSCs are summarized and the film fabrication process strategies for CsPbBr3, CsPbIBr2, CsPbI2Br, and CsPbI3 are systematically discussed, respectively. In addition, the prospects for future film fabrication processes for C-IPSCs are proposed.

Analysis of variation in recombination characteristics due to light and heat in industrial silicon solar cells

This work presents a comprehensive analysis of the variation in performance parameters of monocrystalline and multicrystalline silicon solar cells when subjected to illumination at elevated temperature. Higher degradation and better regeneration in performance parameters namely open circuit voltage (VOC), short circuit current density (JSC) and fill factor (FF) are observed for monocrystalline solar cells. Suns-VOC measurement clearly indicate that the recombination current densities within the space charge region (J02) and rest of the solar cells (J01) together play an important role in light and elevated temperature induced degradation (LeTID) and subsequent regeneration characteristics. During the degradation phase, both J01 and J02 changed significantly for monocrystalline and multicrystalline solar cells. During regeneration, even though J01 improved for both the types of solar cells, notable reduction in J02 was observed only for monocrystalline solar cells. FF loss analysis shows that the recombination in the space charge region is majorly responsible for degradation and regeneration in FF. In contrast to most of the previous studies, we report similar reduction in external quantum efficiency (EQE) at 984 nm, 877 nm and 658 nm and propose that the formation of defects related to LeTID are not only in the deep bulk, but are distributed throughout the bulk. Absence of any improvement in EQE after prolonged exposure to light and heat suggests that defect transformation and gettering are not sufficient enough to regenerate JSC in multicrystalline solar cells. EQE maps at 407 nm suggest that LeTID behavior of emitter is different from that of bulk.

Defect detection and quantification in electroluminescence images of solar PV modules using U-net semantic segmentation

Electroluminescence (EL) images enable defect detection in solar photovoltaic (PV) modules that are otherwise invisible to the naked eye, much the same way an x-ray enables a doctor to detect cracks and fractures in bones. The prevalence of multiple defects, e.g. micro cracks, inactive regions, gridline defects, and material defects, in PV module can be quantified with an EL image. Modern, deep learning techniques for computer vision can be applied to extract the useful information contained in the images on entire batches of PV modules. Defect detection and quantification in EL images can improve the efficiency and the reliability of PV modules both at the factory by identifying potential process issues and at the PV plant by identifying and reducing the number of faulty modules installed. In this work, we train and test a semantic segmentation model based on the u-net architecture for EL image analysis of PV modules made from mono-crystalline and multi-crystalline silicon wafer-based solar cells. This work is focused on developing and testing a deep learning method for computer vision that is independent of the equipment used to generate the EL images, independent of the wafer-based module design, and independent of the image quality.

Automatic detection of multi-crossing crack defects in multi-crystalline solar cells based on machine vision

Automatic detection of multi-crossing crack defects in multi-crystalline solar cells based on machine vision

Downshifting and Antireflective Thin Films for Solar Module Power Enhancement

Efforts to enhance the solar conversion efficiency have prevailed for decades. There is a growing interest in improving the spectral response of solar modules, especially in harvesting UV photons, which offer intense energy in a narrow wavelength range. To harvest UV photons and reduce reflection without interfering with the formulas and manufacturing process of solar cells, in this work, thin films that possess downshifting and antireflection capabilities were fabricated on the cover glass of multicrystalline Si solar cells. The thin films were composed of graded index layers of europium-doped yttrium orthovanadate (YVO4:Eu) and hollow silica nanoparticles (HSNPs). The design of the composite thin films was assisted by the FDTD mathematical model that simulated the refractive index and thickness of each layer to obtain the optimum transmittance. The cover glass with multifunctional thin films harvested more than 30 % of UV photons and enhanced the solar conversion efficiency by 4.12 % at normal incidence compared to the uncoated cover glass.

Effects of surface morphology on Ag crystallite formation in screen-printed multi-crystalline Si solar cells

The electrode collects electrons produced by a solar cell. Ag crystallites generated during front electrode formation play an important role in transferring electrons from the emitter to the Ag finger. Previously, the formation mechanism of Ag crystallites and the various factors influencing Ag crystallite formation have been studied, including the effect of surface morphology on Ag crystallite formation. The glass coverage varies with the texture of the Si surface, and thus the degree of exposure of the Si surface varies correspondingly. When the Si surface is exposed, direct contact is achieved, and contact resistance is improved. However, the effect of surface morphology on the Ag crystallites formed on the Si surface under the glass layer has not yet been studied. The effect of surface morphology on Ag crystallite formation is presented in this work. Two multi-crystalline Si wafers with different surface morphologies were compared. The first multi-crystalline Si wafer was textured using metal-catalyzed chem ical etching (MCCE). The second multi-crystalline Si wafer was textured by MCCE followed by reactive ion etching. Wafers with sharper textures had lower series resistances, higher fill factors, and a large amount of Ag crystallites. Ag crystallites primarily formed at the tips of the texture. To analyze the effect of surface morphology, the surface electron concentration was confirmed by simulation. Electron concentration at the tip was proportional to the sharpness of the tip. Therefore, when the firing process is performed at the same temperature, wafers with sharper tips are expected to exhibit better electrode characteristics.

Efficiency enhancement of p-type multi-crystalline solar cells in different efficiency grades by hydrogenation with electron injection

P-type multi-crystal (mc-Si) solar cells are facing relative weaker competitiveness compared to mono-crystal silicon solar cells due to the efficiency improvement bottleneck. To further enhance the efficiency of p-type mc-Si solar cells, we have systematically investigated the technology of hydrogenation with electron injection (HEI) on p-type mc-Si solar cells with different power conversion efficiency (PCE) grades. Experimental results manifested that the efficiency promotion of cells with higher efficiency (HE) was lower compared to that of lower efficiency (LE) cells under the same HEI processing condition, whether for conventional or passivated emitter and rear cells. Further investigations were carried out to prove that the effectiveness of HEI treatment was closely related to the concentration of both available hydrogen and defect in the bulk of solar cells. This highlighted that the lower concentration of available hydrogen was more helpful for HE cells to improve the electrical performances, which was contrary to LE cells due to the different distribution of defects in the bulk. Besides, programing analysis was implemented to optimize the HEI treatment scheme of HE cells, and the PCE was finally improved by 0.63%rel. ± 0.05%. This result provided an improved technological process to further improve the efficiency gains in the production process, where a classification method was introduced according to the efficiency distribution before HEI treatment. The proposed method can distribute solar cells into appropriate grades to avoid wasting resources in mass production.

Photo-induced hydrogenation and rapid cooling measure on dislocation clusters of multi-crystalline silicon PERC solar cells

The dislocations are the deep level defects with a negative impact on the multi-crystalline silicon (mc-Si) solar cells. Though potential mechanisms of dislocation formation on the silicon ingot have been studied, few investigations consider the effect of LED hydrogenation on dislocation clusters. In this study, we have explored the influence of hydrogenation on the dislocation clusters of large-area (244.34 ± 0.05 cm2) mc-Si solar cells using the high-intensity infrared LED source. However, applying normal cooling measure to hydrogenation will trigger the instability of the hydrogenation improvement effect due to residual thermal stress, so we proposed an appropriate rapid cooling measure (RCM) followed by hydrogenation and achieved optimized results. The results indicated that electrical properties, minority carrier lifetime, current density, power density and external quantum efficiency were enhanced through LED hydrogenation and RCM, and the degradation of mc-Si solar cells also was significantly suppressed. To estimate the content of dislocations after LED hydrogenation and RCM, we applied the X-ray diffraction techniques to calculate the dislocation density using the full-width at half maximum of the rocking curve at (111), (220), (311), (400) and (331) reflections. The dislocation density of mc-Si PERC solar cells was decreased by 0.12 × 108 cm−2 (±0.02 × 108 cm−2) after LED hydrogenation and RCM. Meanwhile, photoluminescence images also illustrated that LED hydrogenation passivated dislocation clusters as well as impurities and defects gathered by dislocations. Therefore, LED hydrogenation of dislocation clusters is an effective measure to improve the performance of dislocation-containing mc-Si solar cells.

Hydrogenation efficiency promotion through manipulating temperature-raising time for multi-crystalline silicon PERC solar cells

Abstract Light injection and cooling conditions can induce some differences in the temperature-raising time of multi-crystalline silicon (mc-Si) solar cells. Through real-time tracking and monitoring of sample surface temperature, the temperature-raising steps for achieving the optimum efficiency improvement and degradation mitigation were optimized and modified. Then the corresponding hydrogenation treatments under a high-intensity infrared LEDs source were carried out based on improved steps. The results indicated that the optimal temperature-raising time should be manipulated at around 60 s and then followed by a 2-min hydrogenation treatment. Furthermore, the temperature-raising process should keep the temperature rising continuously without interruption or temperature drop. However, excessive thermal treatment time damaged the formation of defect precursors and extended the hydrogenation time. Moreover, the Fourier Transform Infrared spectrum curves illustrated that the peak intensity of the Si–H bonds treated at the 60-s temperature-raising time was more significant than that of other temperature-raising time treatments.

Downshifting and antireflective thin films for solar module power enhancement

Efforts to enhance the solar conversion efficiency have prevailed for decades. There is a growing interest in improving the spectral response of solar modules, especially in harvesting UV photons, which offer intense energy in a narrow wavelength range. To harvest UV photons and reduce reflection without interfering with the formulas and manufacturing process of solar cells, in this work, thin films that possess downshifting and antireflection capabilities were fabricated on the cover glass of multicrystalline Si solar cells. The thin films were composed of graded index layers of europium-doped yttrium orthovanadate (YVO4:Eu) and hollow silica nanoparticles (HSNPs). The design of the composite thin films was assisted by the FDTD mathematical model that simulated the refractive index and thickness of each layer to obtain the optimum transmittance. The cover glass with multifunctional thin films harvested more than 30% of UV photons and enhanced the solar conversion efficiency by 4.12% at normal incidence compared to the uncoated cover glass.

Monitoring of Photovoltaic System Performance Using Outdoor Suns-VOC

Summary In-field characterization of photovoltaics is crucial to understand performance and degradation mechanisms, subsequently improving overall reliability and lifespans. Current outdoor characterization is limited by logistical difficulties, variable weather, and requirements to measure during peak production hours. We capitalize on Suns-VOC, which is widely used for laboratory measurements of single solar cells and discuss the barriers in extending the technique to outdoor systems. We demonstrate the normalization of measurements using both backsheet temperature sensors and on-site weather stations. Despite weather variation, VOC, ideality factor, and pseudo fill factor all fall within 1% of the laboratory measurements. It is also demonstrated that monitoring the system VOC at 0.05 to 0.1 suns, during minimal power production, provides a figure of merit that can indicate early degradation of the system. Extensive simulations show that shading portions of a system has minimal effect on measurements, allowing the technique to be used in all weather conditions.

Hydrogenation and Gettering Compatiblep-Type Contacts for Multicrystalline Silicon Cells, Free of Light, and Elevated Temperature Induced Degradation

Results for a room temperature contacting method applied to the p -type rear surface of monocrystalline and multicrystalline solar cell structures are presented. Monocrystalline silicon devices with the rear contacts prepared using the point contacting by localized dielectric breakdown method are reported with an efficiency of 19.2%. The devices show improved measurements of key performance metrics of ρc of 1.6 ± 0.8 mΩcm2 and J 0 c of 2100 ± 650 fAcm−2. This contacting approach is also demonstrated for multicrystalline silicon cells, with no evidence of parasitic breakdown at grain boundary sites. The multicrystalline device implementation highlights a key advantage of this contacting method, namely a relatively free choice of annealing temperature. This flexibility allows process optimization such that the activation of light-and-elevated-temperature-induced degradation is prevented in hydrogenated multicrystalline silicon, while still maximizing the benefits to bulk lifetime.

Carbon-rich amorphous silicon carbide and silicon carbonitride films for silicon-based photoelectric devices and optical elements: Application from UV to mid-IR spectral range

In the work we demonstrated the possibility to apply amorphous non-stoichiometric silicon carbide (a-SixC1-x:H) and silicon carbonitride (a-SixC1-x-yNy:H) films for improvement of exploitation characteristics of silicon-based photoelectric devices and optical elements in very wide spectral range - from UV to mid-IR. The a-SixC1-x:H films possessing optical properties required for effective antireflection (AR) effects for silicon (refractive index (n) at λ = 632 nm from 1.86 to 1.98, optical bandgap (Eopt) from 2.7 to 3.1 eV, and extinction coefficient (k) is close to zero practically in all spectral range) were obtained by PE-CVD from methane, silane, hydrogen, and argon gas mixture. To deposit silicon carbonitride films some amount of nitrogen was added to the gas mixture. For the a-SixC1-x-yNy:H films the following optical parameters were obtained: n = 1.76–1.93, Eopt = 3.1–3.4 eV, k~0. It has been shown that the proposed films possess unique mechanical properties and ratio of the films hardness to their Young modulus is very high (H/E > 0.13). It is evidence of the films high wear resistance that is of great importance when the films are used for protection of silicon optical elements in IR spectral range. It is established that the films of both types are very suitable as excellent AR coatings for silicon in the spectral range of Si-based solar cell photosensitivity, telecommunication windows, and mid-IR. Deposition of even single layer AR film allowed us to reduce reflection losses significantly (reflection coefficient (R) at minimum of reflection becomes close to zero). As a result, efficiency of etched multicrystalline Si-based solar cell (SC) was significantly improved. Transmittance of Si-based optical elements with front and rear AR films reached practically 100% in the telecommunication windows spectral range.

Development of additive-assisted Ag-MACE for multicrystalline black Si solar cells

The uniform distribution of silver nanoparticles on the surfaces of diamond-wire sawn multicrystalline silicon (mc-Si) is critical for the texturing of mc-Si by the Ag metal-assisted chemical etching method (Ag-MACE). In this study, an additive containing alkylphenol polyoxyethylene is developed to improve the Ag-MACE process. It enables an even deposition of the silver nanoparticles over the surface of the silicon wafer, so that the entire wafer surface can be uniformly textured with nanostructures. The experimental results show that the additive improves the appearance and performance of solar cells, including their reflectivity, efficiency, internal quantum efficiency and external quantum efficiency. Mass-produced mc-Si solar cells textured using Ag-MACE with this additive have achieved a maximum efficiency of 19.51%, compared with an efficiency of 19.16% for cells fabricated without the additive.

Classification of Manufacturing Defects in Multicrystalline Solar Cells With Novel Feature Descriptor

The automatic defect recognition for near-infrared electroluminescence images is a challenging task, due to the random shape of the crystal grains and intensity variation in the appearance of multicrystalline solar cell. However, the automatic defect detection systems can meet the growing demand for high-quality products during the intelligent manufacture. Thus, in order to obtain more discriminable defect features under heterogeneous background disturbance, a novel feature descriptor (FD) named as center pixel gradient information to center-symmetric local binary pattern (CPICS-LBP) are proposed, which can fuse the CPICS-LBP by thresholding each pixel of the image into binary code. The defect classification in the heterogeneous background can be dramatically enhanced. Next, the feature description ability of the CPICS-LBP descriptor is analyzed by the gradient map and the experimental results. Furthermore, in order to realize robust extraction of the defect feature, a method named as bag of CPICS-LBP is presented as a global concentrated feature extraction scheme by employing the similarity analysis and clustering of the local image patch features from the image sample. Moreover, the classification accuracy and time efficiency are verified by some experimental results and analysis of solar cells’ image data set. The experimental results show that the proposed methods achieve state-of-the-art classification results.

A 2.4 GHz Rectenna Based on a Solar Cell Antenna Array

Combined solar and radio frequency (RF) harvesting systems are drawing attention by offering self-powered ability to low-power devices, an essential aspect to the success of the Internet of Things. One of the main challenges of these harvesting systems is to improve rectennas efficiency by optimizing the individual energy collection and conversion capacity of each source. To overcome this issue, this letter presents a novel 2.4-GHz rectenna structure for solar and radio frequency energy harvesting applications based on a coplanar antenna array integrated with multicrystalline solar cells, whose aluminum rear terminals are used as radiators for the antenna array. The results obtained by simulations and measurements show that it is possible to collect energy from two different types of sources in a complementary manner, using the rectenna design proposed, making it possible to feed low-power devices remotely.

Enhancement Open Circuit Voltage of Calcium Titanate AR Coated Magnesium Solar Cell

The present research aims to enhance the open circuit voltage of fabricated solar cell through Anti–Reflection (AR) coating on the cell substrate. Solar cell is fabricate using ITO Glass, titanium dioxide, magnesium and redox. Calcium Titanium Oxide (CaTiO3) is chosen as the AR coating material for constructing thin film layer on fabricated solar cell. Selected AR coating material have unique features such as orthorhombic, biaxial, non-radioactive and non-magnetic with electron bulk density of 3.91 g/cm3 respectively. Commonly, voltage generation of the multi crystalline solar cell is low (12% to 14%) due to much reflection of inward sun radiation. Deposition of AR coating on the substrate (fabricated solar cell) can minimize the reflection loss of sun radiation. The maximum improvement in solar cell efficiency after AR coating has been reported as 19.3%. Sputter coating technique is more favorable for thin film coating due to its salient features like uniform coating thickness controlled by time. This uniform coating thickness absorbs more sun radiation. Radio Frequency (RF) magnetron sputter coating technique is utilized in the current research to deposit CaTiO3 on solar cells. Prior to coating, the AR material is pelletized using Universal Testing Machine (UTM). The substrate are coated under varying time duration of 15-minutes, 30-minutes and 45-minutes in order to analyze the variation in open circuit voltage. The deposition of coating on the substrate are confirmed using SEM and FESEM. Open circuit voltage of controlled atmosphere studies for pure and AR coated solar cells (fabricated) are examined. Controlled atmosphere tests of AR coated thin films are conducted by placing the substrate inside a solar simulator and the solar simulator consist of IR thermometer (To measure Temperature), solar power meter (To measure Radiation) and multimeter (To measure Open circuit voltage). Neodym daylight lamp is used to control the radiation in solar simulator. The improvement in cell voltage proves that thin film AR coating considerably minimizes the reflective loss.

Structure-aware-based crack defect detection for multicrystalline solar cells

Automatic crack defect detection for multicrystalline solar cells is a challenging task, owing to inhomogeneously textured background, disturbance of crystal grains pseudo defects, and low contrast between crack defect and background. In this paper, a novel structure-aware-based crack defect detection scheme (SACDDS) is proposed. Firstly, the structure features of crack defect and randomly distributed crystal grains are analyzed, and corresponding mathematical models are used to represent two structure features. Secondly, according to Hessian eigenvalues of the above mathematical models, the identification functions of linear-structure and blob-structure are obtained. Then, a novel structure similarity measure (SSM) function is designed by using the identification functions of two structures, which can highlight crack defect, suppress crystal grains simultaneously. It significantly weakens the interference of inhomogeneous texture and obtains uniform background. Further, in order to overcome non-uniform response of crack region and extract crack defect, a tensor voting-based non-maximum suppression (TV-NMS) method is developed. It improves the uniformity of crack defect response and extracts candidate crack defect pixels. Finally, an effective morphological operation is applied to remove non-crack pixels and complete crack defect can be located in the EL images. Experimental results show that the proposed method can completely extract crack defect in the inhomogeneously textured background, which is well effective and outperforms the previous methods.