Passivated Emitter And Rear Cell Solar Cells Research Articles

Performance optimization of PERC solar cells based on laser ablation forming local contact on the rear

Abstract To improve the photoelectric conversion efficiency (η) of the solar cell, a green wavelength (532 nm) laser source in a nanosecond range was used to ablate the passivated emitter and rear cell (PERC) to form the contact holes. If the laser ablation hole opening process was not set properly, the diameter or the external expansion of holes would be too large, causing the decline of the PERC performance. The Gaussian distribution of the laser is regulated by the output power (P o) and the repetition frequency (f rep) of the incident pulse laser, so that the optimized morphology of holes is obtained on the back of the PERC solar cells. After the contact holes are screen printed by the aluminum paste, the local back surface field is finally formed. The experimental results showed that the outward expansion decreases obviously with the increase of laser P o. Second, the spacing of the holes decreases with the increase of the laser f rep. It was found that under the laser P o of 33.0 W and f rep of 1,400 kHz, the η of the industrial PERC solar cells was the highest. The Quokka simulations indicated that small outward expansion, small diameter, and long spacing of holes would further decrease the recombination parameter in the rear surface. With the optimized morphology of contact holes and the low contact resistance, the PERC cell’s calculated V oc and η improvements were 6.5 mV and 0.48%, respectively, which was verified with experimental findings.

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.

Accelerated damp-heat testing at the cell-level of bifacial silicon HJT, PERC and TOPCon solar cells using sodium chloride

Bifacial passivated emitter and rear cells (PERC) currently have the highest share in the photovoltaic market. However, heterojunction (HJT) and tunnel oxide passivated contact (TOPCon) solar cells are expected to gain significant market share shortly. Despite technological advancements, concerns about the reliability of HJT and TOPCon technologies when deployed in the field still need to be addressed. This work investigates the impact of sodium chloride (NaCl) on damp-heat-induced degradation in bifacial HJT, PERC, and TOPCon solar cells by exposing the solar cells to NaCl before damp heat (DH) testing. It is found that among all investigated cell technologies, TOPCon solar cells degrade the most with maximum power (Pmax) loss of up to ∼75%rel, followed by HJT (Pmax drops ∼50%rel), and PERC cells (Pmax drops only ∼10%rel) after 20 h of DH testing, mainly attributed to an increase in Rs on the front side of TOPCon cells, both sides of HJT cells and the rear side of PERC cells. The front of the PERC and the rear of the TOPCon solar cell are found to be stable. The rise in Rs is attributed to the corrosion of the metal contact, which is caused by a high amount of Na+ and Cl− ions penetrating the metal contact. This corrosion leads to increased porosity, detachment of the contact from the silicon interface, and increased recombination loss in some cases. These results are crucial for all cell technologies as they highlight the potential failures that could occur in the field. Na+ and/or Cl− ions are common contaminants present in solar glass, human fingerprints, soldering flux, rainwater, soil/dust, and seawater. During field operation, these ions have the potential to penetrate and directly interact with solar cells. In our view, the preferred solution is for the solar cells to be corrosion-resistant, which can be rapidly assessed using the method presented in this work.

25.7% efficient PERC solar cell using double side silicide on oxide electrostatically doped (SILO-ED) carrier selective contacts: process and device simulation study

Passivating contacts have recently considered as a superior carrier-selective contact approach for high-efficiency silicon-based photovoltaic devices. However, the conversion efficiencies of the silicon-based passivated emitter and rear cell (PERC) are limited by contact recombination losses that reduce their performance. Therefore, we investigated a new manufacturable silicide on oxide-based electrostatically doped (SILO-ED) carrier-selective contact to suppress the contact recombination losses and reduce the saturation current density (j 0). For the first time, double side electrostatic doping is introduced to the PERC devices to form the carrier selective passivating contacts. First, a conventional PERC device was designed and the effects of surface recombination velocity (SRV) at both contacts were studied. After that, single and double SILO-ED based contacts are introduced into the device and a systematic analysis is performed to understand the tunneling phenomena and improve the conversion efficiency compared to existing PERC cells. The front SILO-ED based device with back contact SRV of 10 cm s−1 showed a power conversion efficiency of 25.4% with j 0 (14.3 fA·cm−2). In contrast, the double SILO-ED device delivered 25.7% conversion efficiency by further suppressing the j 0 to 11.8 fA·cm−2 by implementing SILO-ED approach with two different metal silicides such as erbium silicide (ErSi2) and palladium silicide (Pd2Si) on front and rear contact surface. The champion double SILO-ED PERC solar cell delivered a conversion efficiency of 25.7% with an open circuit voltage (V OC) of 742 mV. The results reported in this study would help to develop superior passivating contact-based PERC solar cells for higher efficiencies.

Progress with screen printed metallization of silicon solar cells - Towards 20 μm line width and 20 mg silver laydown for PERC front side contacts

Within this work, we evaluate and compare different high-end screens for the fine line front side metallization of passivated emitter and rear cell (PERC) solar cells. Three types of high-end screens are considered including (i) a fine mesh screen configuration with a mesh count MC = 520 wires/inch and standard mesh angle of φ = 22.5°, (ii) a knotless screen configuration with a mesh angle of φ = 0° as well as (iii) a knotless screen configuration utilizing a rectangular mesh with different mesh count in warp and weft direction MC = 460/430 wires/inch. Using these advanced screen configurations, all PERC solar cells are metallized with a busbarless fine line front side grid at a nominal contact finger opening of 20 μm and 24 μm. All screen configurations obtained excellent results regarding finger geometry, silver laydown and electrical performance of the front side grid and the fabricated PERC solar cells. The most efficient group obtained a printed mean finger width of 21 μm with a silver laydown of only 19 mg and revealed a mean energy conversion efficiency of 22.7%. Furthermore, we investigate the geometric and electric results of the printed front side contacts in detail using advanced image analysis software and scanning electron microscopy and discuss the impact of the fine line front side metallization on the applicable cell interconnection concepts depending on the series resistance losses. • Evaluation of different high-precision screen configurations for fine line metallization of PERC solar cells. • Reduction of silver laydown to less than 20 mg on the front side while maintaining excellent I–V-results of the solar cells. • In-depth analysis of the geometric properties and electric results of the printed fine line front side contacts. • Discussion of the impact of different screen configurations on various aspects of solar cells.

Enhancement of the conversion efficiency of selective emitter PERC solar cells by post-oxidation

Thermal oxidation has been widely adopted in the fabrication process of silicon solar cells. In this paper, we investigate the effect of thermal oxidation on the performance of passivated emitter and rear cells (PERC) after the diffusion process. It is found that the application of a diffusion furnace for post-oxidation results in the re-doping of phosphorus, which affects the minority carrier lifetime and implied Voc. In comparison, the use of an annealing furnace for post-oxidation brings an improvement of electrical properties of solar cells because of the gettering effect. Furthermore, the increase in thickness of the oxide layer mitigates the laser-induced damage during the laser doping process, which is beneficial for the enhancement of cell efficiency. Batch data shows that post-oxidation using an annealing furnace leads to an absolute efficiency improvement by 0.1%.

Effective way to reduce rear-side potential-induced degradation of bifacial PERC solar cells

While bifacial p -type silicon ( p- Si) passivated emitter and rear cells (PERCs) have dominated the current photovoltaic industry, potential-induced degradation (PID), especially in the rear-side, has become a big issue in their practical applications. Here, we have investigated the impact of different rear passivation layers on the anti-PID and electrical property of bifacial p- Si PERCs. Both simulation and characterization showed that the introduction of SiN x films with a high refractive index and additive oxide films were in favor of reducing the rear PID effect. Finally, we proposed a combined structure of stack films as the rear passivation layer, yielding an absolute front-side and rear-side efficiency improvement of 0.09% and 0.18% with 800 pieces of 166 × 166 mm 2 Si wafers on the production line, and the rear PID related power loss dropped from the baseline of 5.46%–1.05% and 5.15%–0.56% by single-cell modules and commercial glass-glass modules, respectively. Together with the well-solved front-side anti-PID technique in industry, the presented novel rear passivation layer establishes a base for the efficient applications of the bifacial p- Si PERCs. • A combined structure of stack films as the rear passivation layer was proposed for bifacial p-Si PERCs, yielding an absolute front-side and rear-side efficiency improvement of 0.09% and 0.18% on the production line. • The rear PID related power loss dropped from the baseline of 5.46% to 1.05% and 5.15% to 0.56% by single-cell modules and commercial glass-glass modules, respectively. • This work has demonstrated that an invaluable improvement in both anti-PID performance and electrical property can be achieved with the introduction of the novel rear passivation layer to the bifacial p-Si PERCs.

Design and simulations of 24.7% efficient silicide on oxide-based electrostatically doped (SILO-ED) carrier selective contact PERC solar cell

Silicon-based passivated emitter and rear cell (PERC) has emerged as a mainstream high-efficiency cell technology in recent years. However, inherent contact recombination loss becomes the main limiting factor in PERC solar cells, limiting the performance of the PERC device toward higher efficiencies close to the Auger limit of 29.4%. Therefore, carrier selective contacts such as polysilicon on oxide (POLO) have been researched and investigated in the past to mitigate contact-related losses. POLO contacts require a heavily doped polysilicon layer on a thin tunnel oxide layer to facilitate the tunnelling of desired charge carrier electron or hole and simultaneously push the other carrier hole or electron back into the substrate. In this work, single-sided POLO contact-based PERC device is investigated, and an alternative approach is projected to avoid the need for a heavily doped polysilicon layer in carrier selective contacts. Silicide on oxide-based electrostatically doped (SILO-ED) carrier selective contact is designed and examined through extensive device simulation using Silvaco based process and device simulations. Four different devices with a planar or textured surface are designed, such as conventional, single POLO, single POLO with ED, and SILO-ED PERCs to have a comparative analysis. Initially, the influence of surface recombination velocity (SRV) (from 102 to 107 cm/s) on the front surface in the case of a non-POLO PERC device has been investigated. Afterwards, the PERC device by employing single-POLO contact on the front surface has been designed and simulated to obtain 23.95% efficiency. Further, the concept ED is introduced, and 24.6% efficient ED-POLO (with 1 nm thick poly-Si) and 24.7% SILO-ED contact-based PERC devices are designed to avoid the need for a heavily doped polysilicon layer. The SILO-ED-based PERC device with 24.7% conversion efficiency is also compared with the Auger limit (29.4%) for the comparative purpose. The work reported in this research article may pave the way for developing highly efficient PERC solar cells.

Process and device simulations aimed at improving the emitter region performance of silicon PERC solar cells

Achieved levels of silicon-based passivated emitter and rear cell (PERC) solar cells laboratory and module-level conversion efficiencies are still far from the theoretically achievable Auger limit of 29.4% for silicon solar cells, prominently due to emitter recombination and resistive losses. The emitter region in PERC devices is formed by using either ion implantation followed by a diffusion process or POCl3 diffusion. In ion-implanted emitter-based PERC, the process variables such as dose, energy, diffusion time, and temperature play a vital role in defining the characteristics of the emitter region. Detailed investigation of these parameters could provide a pathway to mitigate the recombination as well as resistive losses; however, it requires a considerable budget to optimize these parameters through a purely experimental approach. Therefore, advanced industrial standard process and device simulation are perceived in this work to carry out the comprehensive study of process variables. Investigation of ion implantation and diffusion process parameters on the PV performance of an upright pyramid textured, industrial standard stacked dielectric passivated PERC solar cell is carried out to deliver 22.8% conversion efficiency with improved PV parameters such as short circuit current density (J SC) of 40.8 mA cm−2, open-circuit voltage (V OC) of 686 mV, and fill-factor (FF) of 81.54% at optimized implantation and diffusion parameters, such as implantation dose of 5 × 1015 cm−2 with energy 30 keV followed 950 °C diffusion temperature and 30 min of diffusion time. The performance of the optimized PERC device is compared with already published large area screen printed contact-based device. This work may open up a window for the experimental work to understand the influence of process parameters on the emitter region to develop the highly efficient PERC solar cell in the future.

Performance Improvement of Gallium‐Doped Passivated Emitter and Rear Cells by Two‐Step Bias Application

Passivated emitter and rear cell (PERC) solar cells have dominated the photovoltaic market in recent years. Continuously improving the efficiency of PERC solar cells is of great importance to enable the goal of low electricity cost, which is cheaper than the cost of thermal power generation. Herein, it is demonstrated that a two‐step postfiring bias treatment is able to evidently enhance the efficiency of commercial gallium‐doped PERC solar cells by up to 0.1% absolute. In detail, the first‐step bias treatment is done by forward biasing the PERC solar cells at 12 A and 200 °C for 60 min, resulting in an average efficiency enhancement at around 0.05% absolute. The second‐step bias treatment is done by reverse biasing the PERC solar cells at −0.1 or −0.2 V and at the elevated temperatures for certain times, leading to another average efficiency enhancement at around 0.05% absolute. To explore the mechanism underlying the two‐step bias treatments on improving cell efficiency, a new model in light of hydrogen behavior under electric field is proposed to explain this phenomenon.

Introducing a supercritical fluid technique to reduce passivation layer interface defects in passivated emitter rear contact cells

Improving material and interface defects are an important issue in reducing solar cell leakage current and enhancing their efficiency. From back surface field (BSF)-based solar cell to passivated emitter and rear cell (PERC), solar cell structures have been designed to reduce defects. In this study, a supercritical fluid (SCF) technique is applied as a low temperature defect passivation technology to passivate defects in a PERC solar cell, enhancing device performance. Owing to the high penetration and high solubility of the supercritical fluid, hydrogen is the passivation source carried into the device to passivate Al2O3/Si interface defects. Furthermore, electronic analysis is used to confirm the benefits of the SCF treatment on the solar cell properties of open-circuit voltage (Voc), short-circuit current (Jsc), fill factor (FF), efficiency, power (Pmax) and series resistance (Rs), all measured under a standard light source. Finally, a model is proposed to explain how the SCF treatment passivates interface defects and enhances device performance.

Tuning back side passivation for enhancing the performance of PERC solar cells

In the mono-crystalline silicon passivated emitter and rear cell (PERC), the back side passivation film made up of Al2O3 + SiNx:H stacks is the mainstream design. In this paper, the effect of the thickness of Al2O3 passivation layer on the performance of the solar cell was studied, and the correlation between the refractive index (RI) of SiNx:H layer and the efficiency gain of the solar cell after regeneration was analyzed. The results indicate that the thickness of Al2O3 layer needs to be balanced between the surface passivation and bulk passivation of SiNx:H, and the lower RI of SiNx:H layer shows a better hydrogen passivation capability. During the restoration of the solar cell efficiency, a thinner Al2O3 layer facilitates a faster stabilization of the boron-oxygen complexes. Finally, a new five-layer SiNx:H film was designed for the back side passivation film, and a conversion efficiency of 22.56 % was achieved, which is 0.05 % higher than that of the solar cell with a single-layer SiNx:H film.

Light management of PERC solar cell with the front and back dielectric multilayers

AbstractLight management is one of the important methods to increase the efficiency of passivated emitter and rear cells (PERCs). With the help of simulation, we designed and fabricated the industrial Ga‐doped single‐crystalline silicon (sc‐Si) PERC solar cells by integrating the silicon oxynitride (SiOxNy) with the traditional silicon nitride (SiNx) dielectric films on both the front and rear surfaces. In the front, the SiOxNy capping effectively decreased the reflectance in the short‐wavelength light range, thus increased the cells' short circuit current (Isc) by ~50 mA. In the back, the SiOxNy layer was inserted into the rear SiNx film, thus increased the internal reflection at the rear surface in the long‐wavelength light range, resulting in an about 24‐mA Isc gain. Totally, with the front and rear light management, the champion samples showed the significant improvement with an about 80‐mA increment in Isc of cells compared with the baseline group.

Design investigation on 100 μm-thickness thin silicon PERC solar cells with assistance of machine learning

Thin crystalline silicon passivated emitter and rear cell (PERC) solar cells are a very prospective technology for next-phase photovoltaic development due to the potential of high cost effectiveness. The reduction of silicon wafer thickness can significantly save the costs, but there is a loss of cell efficiency if cell design is not conducted. For the thinned 100 μm-thickness PERC solar cells without design, the efficiency loss is pronounced from commercial 180 μm-thickness. In this paper, we have designed and optimized SiO2/SiNx/SiNx/SiOx thin films (here two SiNx layers have different refractive index) on the front surface and SiNx/SiOx thin films on the back surface for the standard front single-sided textured PERC cells. Based on this, we further design and investigate the case of double-sided textured PERC solar cells. Compared with the reference cell, the present designs can lead to the short-circuit current density increase by 0.6 mA/cm2 and the open-circuit voltage enhancement by 10 mV for the front textured case, which causes the efficiency gain of 0.7% from 21.6% to 22.3%. For the double-sided textured cells, the efficiency has an extra increase of 0.6% from 22.3% to 22.9%. Finally, we have constructed the efficiency prediction model by using the multilayer perceptron algorithm in machine learning. It is found from the SHAP values that a significant effect of the front SiNx thickness is observed to predict the performance of the PERC cells.

Ga-doped Czochralski silicon with rear p-type polysilicon passivating contact for high-efficiency p-type solar cells

The use of Ga-doped Czochralski (CZ) silicon wafers in Passivated Emitter and Rear Cells (PERC) has been confirmed to have a prominent advantage in suppressing light-induced degradation (LID), which will attract considerable attention for the application of Ga-doped wafers in more efficient photovoltaic devices. In this work, we investigate the passivation quality and address the issue of LID in Ga-doped CZ Si wafers equipped with p-type polysilicon passivating contact that consists of an ultrathin SiO x and a heavily doped polysilicon. We also present the modeling results for solar cells using this type of contact. The experiments show that samples with Ga-doped CZ Si wafers have superior anti-LID properties when compared to the samples with B-doped wafers. An excellent passivation performance with a high implied open-circuit voltage ( iV oc ) of 705 mV and a low single-sided saturation current density ( J 0,s ) of 9 fA/cm 2 was achieved. Moreover, with the help of the numerical simulations, we predict that the p-type Ga-doped CZ Si solar cells with p-type polysilicon passivating contacts have the potential to achieve a high efficiency of 23.8%, an ~0.5% absolute efficiency improvement over that of PERC solar cells. The results demonstrated in this study suggest that Ga-doped CZ Si wafers combined with p-type polysilicon passivating contacts could resolve the LID issue while maintaining good passivation properties, providing a promising alternative for p-type solar cells in the photovoltaic industry. • The p-type TOPC on featuring Ga-doped CZ Si wafers achieved an excellent passivation quality with iV oc > 705 mV. • The passivation improvement sources of Ga-doped CZ Si-based structures were attributed to the suppression of B- and O-related defects. • Ga-doped TOPCon solar cells show the LID-free performance. • Simulation results show a comparable efficiency of 23.8% for Ga-doped TOPCon solar cells.

Status of Al2O3/TiO2‐Based Antireflection and Surface Passivation for Silicon Solar Cells

Inhibiting charge recombination effectively by surface passivation is very important for high‐efficiency silicon solar cells. With the emergence of passivated emitter and rear cells (PERCs), which surpass conventional solar cells, the need for a novel passivation scheme is increasing. Passivation layer stacks using negatively charged Al2O3 have been applied successfully to realize high‐efficiency PERC solar cells. Herein, the developments of surface passivation by Al2O3/TiO2‐based layers are reviewed. The topics range from synthesis methods and optical properties as antireflection coatings to the electrical properties related to the material, interface, and passivation quality. Ultrathin Al2O3/TiO2‐based layers generally feature a combination of field‐effect passivation by negative fixed charges, a low interface defect density, and adequate humidity stability. Among the various deposition methods, atomic layer deposition is focused on, which can form dual layers and nanolaminates. How the features of atomic‐layer‐deposited Al2O3/TiO2‐based layers can be utilized for interface engineering and tailoring the properties of surface passivation schemes is discussed.

Suppression of potential-induced degradation in monofacial PERC solar cells with gradient-designed capping layer

The potential-induced degradation (PID) of p-type crystalline silicon passivated emitter and rear cell (PERC) is a critical issue causing severe output power loss. In this paper, a gradient-designed capping layer consisting of silicon nitride/silicon oxynitride/silicon oxide (SiNx/SiNxOy/SiOx) is proposed as the surface coating for p-type PERC solar cells. The capping layer improves the short wavelength spectral response due to its better anti-reflection effect. An impressive efficiency of 23.52% has been achieved on mass production line. A long-term PID evolution up to 672 h is performed for glass/back sheet PERC cell modules under stringent conditions with the ambient temperature of 85 °C, relative humidity of 85%, and the applied voltage of 1500 V. The current–voltage (light I-V, dark I-V) parameters of the modules were measured, as well as the electroluminescence, to evaluate the effect of sodium ion migration in PERC solar cells. It is shown that monofacial PERC solar modules suffer from shunt of PN junction under PID stress, which can be obviously suppressed by gradient-designed capping layers. The optimized PERC solar modules show excellent PID resistance, showing great potential for lower levelized cost of energy (LCOE) of photovoltaic power generation.

Kinetics of light and elevated temperature-induced degradation in cast mono p-type silicon

Cast mono Silicon (Si) technology has the advantages of low cost, i.e., multicrystalline silicon (mc-Si), and high efficiency, i.e., Czoch-ralski-grown silicon (Cz-Si). Cast mono Si has a similar performance to current Cz-Si counterparts with a solar cell structure, i.e., a passivated emitter and rear cell (PERC). However, the severity of light and elevated temperature-induced degradation (LeTID) on cast mono Si solar cells may be similar to mc-Si, not Cz-Si. To clarify the LeTID kinetics in the p-type cast mono silicon, we observed the effect that LeTID had on the carrier lifetime. First, a series of carrier lifetime measurements were performed to investigate LeTID kinetics in the accelerated regeneration process via high intensity illumination at elevated temperatures and modulating kinetics via dark annealing before illumination. Next, we documented the evolution of a carrier lifetime to investigate the stability of regenerated state at 75 °C and light intensity of ~ 1 kW/m2. The results show that the effect of dark annealing on LeTID kinetic modulation could be explained by the B-H defect precursor concentration and defect reservoir theory, which originate from the results for mc-Si. An accelerated regeneration method that combines dark annealing and illumination, with high intensity at an elevated temperature, can yield a higher value and improved LeTID stability in terms of the lifetime, as compared with illumination without pre-annealing. This implies that this mixed process may be a potential method to provide both improved performance and high anti-LeTID properties in Si PERC solar cells.

Passivated Emitter and Rear Cell Silicon Solar Cells with a Front Polysilicon Passivating Contacted Selective Emitter

p‐Type silicon solar cells with a structure of passivated emitter and rear cell (PERC) are a mainstream product of the photovoltaic (PV) industry. Because of its low cost, PERC technology will continue to be dominant for a long time. One of the key features to improve PERC solar cell performance is the use of a selective emitter (SE), which is now mainly realized by laser doping (LD). However, SE by LD still cannot perfectly resolve recombination underneath the front metallized area. The use of a tunnel oxide passivated contact (TOPCon) can dramatically reduce recombination at the metallized area. With the help of an organic mask and etching by texturing solution, the TOPCon SE structure on PERC cells is realized. An average efficiency of 22.65% is reached on 6 in., commercial grade p‐type Czochralski wafers. The average open‐circuit voltage of PERC cells with TOPCon SE is 14.6 mV higher than LD SE. However, the short‐circuit current is lowered by parasitic absorption of polysilicon of alignment margins, which makes cell efficiency of the two SE structures almost the same. With improved alignment precision, TOPCon SE will provide an increase in efficiency.

Thermal Laser Separation of PERC and SHJ Solar Cells

This article investigates thermal laser separation (TLS) on p-type Czochralski-grown silicon (Cz-Si) passivated emitter and rear cells (PERC) and n-type Cz-Si heterojunction (SHJ) solar cells. The TLS comprises of two laser-based processes: the crack initiation by a scribe laser and the crack propagation by a cleave process leading to separated cells with smooth edge surfaces. The sole impact of the cleave process on the cells' passivation layers is examined by performing it without the initial scribe, not separating the samples. By means of photoluminescence imaging, different cleave laser powers PC on passivated PERC and SHJ cell precursors are investigated, and the optimum PC values are then chosen for the processing of metallized and fired host cells with half cell and shingle cell layouts. Both, the cleave process as well as the complete TLS process are then separately performed in order to investigate the effect of each individual process by SunsVOC measurements taken before and after processing. For monofacial PERC cells, a drop in pseudofill factor ΔpFF = - 0.3%abs is recorded after TLS of the host cell into five shingle cells with 31.35 mm cell width. The effect on bifacial SHJ cells is stronger with ΔpFF = - 2.1%abs. Thereby, the cleave process itself does not induce significant losses in the cell performance for both cell types. The main losses are attributed to the recombination at the newly created unpassivated edges after complete TLS.