Multicrystalline Silicon Solar Cells Research Articles

Improving the short wavelength response of the multi-crystalline silicon solar cell by using 10% Erbium doped ZnS nanoparticle-based downshifting layer

This study describes how a polymer/ZnS composite layer with antireflection, scattering, and downshifting properties improved the short wavelength response of multi-crystalline silicon (mc-Si) solar cells. The downshifting layer is made up of 10% erbium-doped ZnS nanoparticles that are dispersed in a PMMA matrix at concentrations ranging from 1 mg/ml to 10 mg/ml and applied by spin coating to the front surface of an mc-Si solar cell. The chemical route method is used to create the 10% erbium-doped ZnS NP. XRD, SEM, UV–Vis, and PL techniques are used to identify the synthesized NP. EQE, IQE, reflectance, and J-V measurement serve as distinguishing characteristics for mc-Si solar cells with and without a downshifting layer. The cubic structure of the nanoparticle has been confirmed by the XRD pattern of 10% erbium-doped ZnS NP. The spherical shape of the nanoparticle was visible in the SEM image. The nanoparticle's ability to absorb high-energy photons and release low-energy photons that met the downshifting requirement was confirmed by the UV–Vis and PL spectra. Solar cells with a downshifting layer expose their EQE spectra to enhance their UV response at short wavelengths. Both EQE and J-V measurements are used to calculate the short circuit current density. In the EQE and J-V measurements, it differs from the bare one by 4.76% and 3.57%, respectively. The short circuit current density has confirmed that the 3 mg/ml amount of ZnS:10 %Er NP/PMMA used as a downshifting layer in this study is the right concentration to improve the short wavelength response when applied to the top surface of the mc-Si solar cell.

Modelling and Optimization of A Light Trapping Scheme in A Silicon Solar Cell Using Silicon Nitride (SiNx) Anti-Reflective Coating

Solar cells system has been gaining remarkable attention in the photovoltaic (PV) industry in recent years. Therefore, many people used solar cells in their life. Hence, from time to time, many industries keep improve it to get the best of efficiency of the solar cell. In this work, it presents ray tracing of light trapping (LT) schemes in thin c-Si to enhance broadband light absorption within 300 - 1,200 nm wavelength region. For the ray tracing simulation, mono c-Si wafer with 100 μm thickness is investigated and solar spectrum (AM1.5G) at normal incidence is used. Random planar and upright pyramid front surface with silicon nitride (SiNx) anti-reflective coatings (ARC) with the difference thicknesses are the LT schemes being studies in this work. The broadband anti-reflective coating can effectively reduce the optical loss and improve the energy efficiency in the solar cells. The optical properties of the thin c-Si are analyzed with incremental LT schemes. Not only that, the current density also calculated from the absorption curve. Optical properties and current density were evaluated to find out the best thickness and refractive index of the silicon nitride (SiNx). The initial simulation results show that the solar cell current density is about 24.81 mA/cm2. A great Jmax enhancement in solar cell was achieved with utilizing the ARC thickness and type of front surface. Among the 6 proposed scheme, the scheme with upright pyramid front surface of 75 nm SiNx ARC thickness realized a good improvement in current density of 41.19 mA/cm2. This leads to Jmax enhancement of 66.02 % when compared to the reference c-Si. HIGHLIGHTS Solar cell energy conversion efficiencies for commercially available multicrystalline silicon solar cells are around 14 - 20 % which still insufficient Energy conversion efficiency of solar cell can be enhanced by adding the anti-reflective coating on the front layer of light trapping scheme SiNx as a single layer anti-reflective coating with a certain thickness shown a good behavior in reducing the light reflection hence, effectively absorbing more light into the scheme and leads to enhancing the energy conversion efficiency GRAPHICAL ABSTRACT

Numerical and Experimental Study of the Front Surface Recombination Velocities and Base Widths Effect in Multi-Crystalline Silicon Solar Cell Quantum Efficiency

Photovoltaic research activities are related to material innovation that can be obtained at a comparatively low cost. Semiconductor p-type multi-crystalline Czochralskyc (CZ)-grown silicon wafers were used in this study. The effects of front surface recombination velocities and base thickness in solar cells’ quantum efficiency are theoretically calculated. The results denote that both the surface recombination velocities and the base widths significantly impact the quantum efficiency. The results are of universal technical importance in designing solar cells and their surface structures. The main goal of this paper was to confirm the validity of the above theoretical calculations; for this purpose, silicon solar cells with front-thin porous silicon and rear interdigitated contact have been produced. A good agreement was obtained between experimentally obtained solar cells’ quantum efficiency data and the theoretical results. Therefore, the quantum efficiency of the mc-Si solar cells with porous silicon and rear interdigitated contact was enhanced up to 25% at 580–1100 nm wavelength range and up to 50% at short wavelength (400–570 nm), compared to reference mc-Si solar cells. The obtained results indicate that the rear interdigitated contact maximizes the surface area of the metal contact and improves the current collection. At the same time, the porous silicon layer passivates the front surface and reduces recombination losses.

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.

Impurity analysis of the effect of partial replacement of retort with an insulation material on mc-silicon grown in directional solidification furnace: Computational modeling

A transient global model has been created for modified directional solidification system. Since the efficiency of the solar cell mainly depends on the quality of the multi-crystalline silicon, it is important to modify the directional solidification system and to optimize the parameters. In multi-crystalline silicon solar cell, the concentration and segregation of impurities and precipitates plays a vital role in the conversion efficiency. Scalar parameters have been used to analyze the concentration and segregation of impurities in the grown mc-Si. The computation was developed to clarify the distributions of oxygen, carbon, nitrogen and silicon carbide. Five cases were discussed whereas except conventional case, all other cases show better results to grow good quality mc-Si ingot for solar cell applications.

Effects of beam splitting on photovoltaic properties of monocrystalline silicon, multicrystalline silicon, GaAs, and perovskite solar cells for hybrid utilization

ABSTRACT Photovoltaic-thermal beam-splitting hybrid system utilizes solar energy with a high efficiency in a wider spectrum than photovoltaics. However, few studies explain the selection of solar cells or consider perovskite solar cells for the hybrid system. In this work, we studied the effects of beam splitting on the photovoltaic properties of monocrystalline silicon, multicrystalline silicon, GaAs, and perovskite solar cells with beam splitters to determine their applicability to beam-splitting hybrid systems. Transmission wavelengths of the beam splitters are 400–714 nm, 410–802 nm, 420–840 nm, and 430–1100 nm, respectively. Open-circuit voltage, fill factor, short-circuit current density, maximum power, and power conversion efficiency of solar cells with and without beam splitters were compared. Additionally, external quantum efficiency curves of the solar cells were presented to explain the trends of and to compare the preceding parameters. Results show that the Si solar cells is ineffective for the beam-splitting hybrid utilization with general beam splitters for their wide spectral response range, and the GaAs solar cell is better for its short spectral response range, and beam splitting can improve its power conversion efficiency. Meanwhile, the perovskite solar cell shows a great potential for hybrid utilization.

Analytical Modeling of the Temperature Sensitivity of the Maximum Power Point of Solar Cells

This article presents new analytical expressions for the temperature coefficients of the voltage, current, and power of a solar cell at its maximum power point (MPP). A new analytical expression of the temperature coefficient of the fill factor is also derived. The new expressions are written as functions of photovoltaic (PV) metrics that can be obtained from i-V measurements. Nonideal diode behavior is partially accounted for through a temperature dependent ideality factor. The recombination parameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\gamma$</tex-math></inline-formula> , which has been shown to account for the thermal sensitivity of all mechanisms determining the open-circuit voltage, appears to play a role also for the temperature coefficient of the MPP. The expressions are tested against experimental data, which covers measurements from 18 multicrystalline silicon solar cells with different bulk resistivities and cell architectures. It is found that the new model captures the essence of the temperature variation shown by the investigated PV metrics.

Comprehensive cell to module optical loss analysis of metal assisted chemically etched inverted pyramid textured multi-crystalline silicon solar cells and modules by ray-tracing method

Most of the recent articles addressing the texturing issues of diamond wire sawn multi-crystalline silicon (mc-Si) wafers propose metal-assisted chemical etching (MACE) inverted pyramid texturing scheme as the best suited industrial process for the fabrication of low-cost, high efficiency solar cells. However, a detailed generation loss analysis of such textured solar cells are not widely investigated yet, especially after module conversion. We present a comprehensive analysis of various optical losses in MACE inverted pyramid textured mc-Si solar cells and modules using the SunSolve module ray-tracer simulator from PV Lighthouse. The simulation model accurately predicted the optical properties of MACE inverted pyramid textured samples and the simulated reflectance values were nearly identical to experimentally measured values at different stages of solar cell processing (before and after ARC). This study quantifies and benchmarks the optical generation losses of not-encapsulated and encapsulated inverted pyramid textured cells with well established models of random pyramid textured and iso-textured solar cells for aluminum back surface field (Al-BSF) architecture. Moderate cell to module (CTM) generation current loss was noticed for inverted pyramid textured solar cells, which was nearly 0.71 mA-cm−2 lower than random pyramid textured and 1.05 mA-cm−2 higher than iso-textured solar cells. We find that adoption of MACE inverted pyramid texturing over acid texturing enhances the photo-generation in mc-Si modules by ∼0.5% and that the total photo-generation current density in mc-Si solar modules approach 99.6% of that in random pyramid textured c-Si modules.

Perovskite Solar Module Outdoor Field Testing and Spectral Irradiance Effects on Power Generation

One of the challenges facing the industrialization of perovskite solar cells (PSCs) is the lack of outdoor field‐testing evaluation, especially for large‐scale perovskite solar modules. Herein, the real‐world operating performance of an efficient PSC module in the rooftop field test is characterized and analyzed. The maximum power point of a 125 mm × 125 mm PSC module, with a power conversion efficiency (PCE) of 10.34%, is tracked outdoors. Meanwhile, the weather information is recorded, which enables us to investigate the correlation between specific outdoor factors and the device performance. Compared with the multicrystalline silicon (mc‐Si) solar cell as a reference, the PSC module is more sensitive to outdoor solar spectral variations due to its narrow absorption region. Furthermore, benefitting from the long‐wave bump and redshift of the spectral, the available energy ratio of PSC module increases in the morning and afternoon hours, and its performance ratio (PR) value increases accordingly. During the test, the PR of PSC module reaches a maximum of 92.3%, an average of 5% higher than that of the mc‐Si counterpart.

Research progress of light and elevated temperature-induced degradation in silicon solar cells: A review

At present, passivated emitter and rear cell (PERC) solar cells dominate the photovoltaic industry. However, light and elevated temperature-induced degradation (LeTID) is an important issue responsible for the reduction of PERC efficiency, which may lead to up to 16% relative performance losses in multicrystalline silicon solar cells, and this degradation occurs in almost all types of silicon wafers. Even in next-generation silicon solar cells like Tunnelling oxide passivated contact (TOPCon) and Heterojunction with Intrinsic Thin-layer (HJT) solar cells, LeTID can still cause an efficiency loss up to 1% relative. LeTID is a long process in terms of time during the whole cycle of degradation and regeneration, which will seriously affect the conversion efficiency and stability of solar modules, and hence increase the cost of electricity generated by solar cells. Furthermore, after years of research on LeTID, researchers are yet to determine the specific cause of LeTID. In this paper, we refer to specific literature, briefly describe the development history of LeTID, introduce the phenomena of LeTID in crystalline silicon solar cells, and describe its characteristics. In addition, we also analyzed the fundamental causes of LeTID, and found that the cause may be related to metal impurities or hydrogen contained in solar cells. At present, in view of the participation of hydrogen in LeTID and other existing related theories, this paper introduces several methods to inhibit LeTID in crystalline silicon. Finally, the content of this paper is summarized, and the development of solar cells in the future is prospected.

Experiment and theoretical prediction for subsurface microcracks and damage depth of multi-crystalline silicon wafer in diamond wire sawing

Diamond wire saw slicing is an important process of multi-crystalline silicon (mc-Si) solar cell substrate processing. In wire sawing of silicon crystal, the brittleness removal of materials will lead to subsurface microcrack damage, reduce the fracture strength, increase the breakage probability of the as-sawn wafer and affect the subsequent surface etching texture of wafer. In this paper, a mathematical model calculating subsurface damage depth (SSD) of mc-Si is established based on the analysis of subsurface crack system in diamond wire sawing process. The correctness and rationality of the model are verified by experiments. Then, the model is used to predict the variation trend of the microcracks number (CN) and subsurface damage depth under different process parameters and saw wire parameters. The results show that the SSD decreases and CN increases with the increase of wire speed and decrease of feed speed; With the increase of abrasive density on wire surface, the SSD decreases and CN increase. The change of abrasive average size has little effect on the SSD and CN; a smaller abrasive size range is beneficial to reduce the SSD and increase CN.

Recovery of potential-induced degraded p-type multicrystalline Si PV modules by application of a reverse DC bias

Potential-induced degradation (PID) of photovoltaic (PV) modules based on p-type crystalline Si occurs in large-scale PV systems. The development of a low-cost PID recovery technique is important to maximize the power generation capacity of PID-affected facilities. In this paper, we study a simple PID recovery method for multicrystalline silicon solar cells. PID recovery was conducted by application of a reverse DC-bias voltage to the p-n junction of solar cells in PV modules, without temperature control devices. By using this method, the conversion efficiency of solar cells reduced to approximately 20% of their initial value via a PID test was recovered up to 92%. Additionally, nonuniform temperature increases of PV modules by leakage current were observed during the voltage application.

Improve solar cell performance of high-performance multicrystalline silicon seeded with low-cost compact nucleation layer

In order to further improve the quality of high efficiency multicrystalline silicon and the performance of multicrystalline silicon solar cells, we designed a compact nucleation layer on the crucible bottom for casting high performance multicrystalline silicon ingots. The morphology of nucleation grains, the minority carrier lifetime mappings and the defects were analyzed and compared with that of the conventional nucleation layer. The results show that the initial nucleation grains of the compact nucleation layer were finer and more uniform, and there are fewer grains with high defect density at the ingot bottom，which is beneficial to reduce the defect ratio of the whole ingot. Moreover, the solar cell efficiency and electrical performance parameters, such as Rsh was also discussed. It was found that the Rsh has a great impact on the efficiency of multi-busbars solar cells, and the average solar cell conversion efficiency of the wafers grown with the compact nucleation layer is 0.11% higher than that of the wafers grown with the conventional nucleation layer.

Damage and residual layer analysis of reactive ion etching textured multi-crystalline silicon wafer for application to solar cells

As part of the surface texturing process of multi-crystalline silicon solar cells, isotropic etching is performed by using an acidic solution. Furthermore, metal catalyst chemical etching (MCCE), reactive ion etching (RIE), and laser etching are used to further decrease surface reflectance. This study aimed to increase the power conversion efficiency of the solar cell by improving the short-circuit current density (Jsc) using MCCE and RIE. During RIE, a byproduct and a plasma damage layer are formed on the silicon surface, which decrease the efficiency of the solar cell and therefore need to be identified and effectively removed. Transmission electron spectroscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses were performed to identify the byproducts formed during RIE to confirm that it was amorphous silicon oxide. Furthermore, an etching process using acidic and alkaline base solutions was used to remove the plasma damage layer and the Jsc loss was calculated using the reflectance. As a results, confirm a difference of up to ∼ 1.6 mA/cm2, and an improvement of approximately 0.6% was observed in the solar cell efficiency. These results show a method of minimizing Jsc loss and removing surface damage in a silicon solar cells fabricated using the RIE method.

Emitter Quality Optimization Using Lightly Doped Phosphorus Diffusion and Thermal Oxide Anneal for Cell Efficiency Improvement in Multi-Crystalline Black Silicon Solar Cells

Improving solar cell performance by increasing solar cell efficiency by various process optimization had always been a simple straight-forward methodology followed in a R&D or in a solar cell manufacturing company. This is also the most cost-effective practice to improve a product performance using the same technology without the need to procure alternative or expensive raw materials or by adopting advanced solar cell processing techniques. Aluminium Back Surface Field (Al-BSF) technology using multi-crystalline wafers (mc-Si) had been a well-established and a dominant product in the solar industry for more than two decades. However, as the industry progresses, the demand for high efficiency solar cells and modules started going up and full area Aluminium BSF based cells suffers from a lot of inherent limitations on cell efficiency. This is primarily due to the intrinsic high density of crystal lattice defects or otherwise called as grain boundary defects present dominantly only in mc-Si wafers. These grain boundaries tends to accumulate several defects and become trap centres which cause high recombination for minority carriers thereby exhibiting lower conversion efficiency and higher dispersion in electrical parameters in batches of tested cells. Years of research using this material have helped to derive the maximum benefits using this mc-Si wafer in producing industrial full area BSF cells and we can say with certainty that the efficiency potential has reached the saturation point with this technology. An interesting development that happened in the area of improving the final product performance using mc-Si wafers at both cell and module level, is by replacing the conventional acid texturing process with an introduction of a nano-texturing process called Metal Catalysed Chemical Etching (MCCE) using specialized chemicals which improves the light trapping capabilities by creation of inverted pyramid texture on the silicon wafer surface and thereby enabling the wafers to absorb sunlight over a broader range of wavelength and incident angle. With this development done in mc-Si wafers in recent past, it is still a daunting task to surpass cell efficiencies beyond 19.0% using this wafer source. Hence for cell manufacturing lines which use mc-Si wafers, there is always a constant need to improve the cell manufacturing processes to reduce the impact of poor intrinsic quality of mc-Si wafers and improve the final product performance without adding any significant cost factor.

Recommendations on the preparation of silicon solar cell samples for defect etching

Research on the structural defects of silicon such as grain boundaries and dislocations, their spatial distribution and how they impact the resulting solar cell performance often proceed by polishing the sample, etching to reveal the dislocations and grain boundaries, and then scanning the surface to image the defects and record their corresponding positions. While a lot of work has been devoted to developing appropriate etches and how to correlate the etch pits to cell performance, materials pertaining to preparation of samples for defect etching, which is a crucial step to ensure successful imaging and analysis, are limited. This work describes a method of polishing multicrystalline silicon solar cell samples in preparation for defect etching. The method described herein:• Utilizes both mechanical and chemical mechanical polishing.• Can be applied to both fabricated silicon solar cells and as-cut wafers.

Anti-reflection effect of large-area ZnO nano-needle array on multi-crystalline silicon solar cells

The current diamond-wire-sawed multi-crystalline silicon wafer lacks an effective light trapping structure, which results in high reflectivity and hinders the improvement of efficiency. In this work, we proposed an enhanced light trapping structure outside the junction of multi-crystalline silicon solar cells, that is, constructing a ZnO nano-needle array on the surface of the textured multi-crystalline silicon to minimize the reflection in the visible-near infrared band to achieve light trapping effect. Solar cells with ZnO nano-needle structure exhibit excellent light trapping performance over a wide band (350–1100 nm). The low-cost and simple preparation method makes this enhanced light trapping structure has broad application prospects.

A comprehensive investigation of the potential of metal assisted chemical etched (MACE) nano-textures over conventional micron-sized iso-textures for industrial silicon solar cell applications

We present a comprehensive comparative analysis of acid textured and MACE (Metal Assisted Chemical Etching) nano-textured multi crystalline silicon (mc-Si) solar cells processed in an industrial cell line in terms of performance parameters. The batch average open circuit voltage of nano-textured solar cells was marginally lower and the measures for improving the same are discussed. Batch average short circuit current (JSC) and fill factor (FF) were respectively 0.65 mA-cm−2 and 0.7% (absolute) higher for MACE nano-textured solar cells. Significantly lower surface reflectance in MACE nano-textured cells in the blue and near infrared regions are found to be the reason for the enhancement in JSC. The main component of FF gain is identified as the lower series resistance in MACE cells. The contact formation mechanism in screen printed mc-Si solar cells, investigated using scanning electron microscopy, revealed that the elevated portions at the boundaries of the textures act as favorable sites for silver crystallite precipitation. A larger areal density of such sites is observed on the MACE nano-textured surface than in case of acid textured solar cells, leading to a much lower series resistance. The results suggest the potential for the application of MACE in the more popular mono-crystalline silicon cell technology for further reduction of contact resistance. Alternatively, MACE may be used to obtain similar contact resistance with lower amount of silver paste, compared to iso- and pyramid textured solar cells.

Carrier-Density-Wave Multiple Lifetime Imaging in a Multicrystalline Silicon Solar Cell Using Quantitative Heterodyne Lock-In Carrierography and Localized Current–Voltage Characteristics

Trap-state kinetic parameters of a multicrystalline silicon solar cell were investigated using dynamic heterodyne lock-in carrierography (HeLIC) imaging under various conditions of illumination intensity and load resistance. Physical relaxation times associated with free-carrier-density-wave (CDW) band-to-band recombination, capture in and emission from two intraband-gap traps were obtained and imaged using camera-based HeLIC pixel frequency responses and a nonlinear rate equation model which provided physical insight on dynamic interactions between the CDW and the traps in the solar cell. An optoelectronic analog to the conventional diode equation was used to determine the solar cell parameters and, thus, enable the measurement of local I–V characteristics imaged over the device surface. The dc photoluminescence image at an open circuit was used as a reference and its pixel statistics and electrical parameters (maximum power, series resistance, saturation current, and generation current) were imaged using the optoelectronic equivalent of the electrical Shockley equation. The optoelectronic lifetime images were then compared with lifetime images derived from these electrical solar cell parameters and the effects of the trap states were explored. Regions with maximum power were found to be associated with low trap concentrations exhibiting low thermal emission and capture rates, with the surface/shallow trap density affecting the maximum power. The trap type (surface versus bulk) limiting the solar cell maximum power was found to vary under different values of photovoltage from open circuit to short circuit.

In-depth analyses of p-type silicon solar cells: A comparison between commercial compact and laboratory LIBS systems

We report on the quality control of multicrystalline silicon (mc-Si) solar cells by laser-induced breakdown spectroscopy (LIBS). A commercial LIBS-6 compact system operating at 1064 nm was compared to a laboratory LIBS system operating at the same wavelength equipped with an Echelle spectrometer. A depth profiling analysis was performed to understand the distribution and diffusion of trace transition metallic impurities in the volume resulted from polysilicon and ingoting processes and mc-Si wafers fabrication. Eight elements were detected in this analysis, which are Silicon, Silver, Aluminum, Calcium, Magnesium, Sodium, Potassium and Hydrogen. Comparing to other analytical techniques, LIBS has the best advantage for a rapid depth profiling, with high layer-by-layer resolution, without significantly altering the sample.