Rear Contact Solar Cells Research Articles

Enhancing Reliability and Regeneration of Single Passivated Emitter Rear Contact Solar Cell Modules through Alternating Current Power Application to Mitigate Light and Elevated Temperature‐Induced Degradation

The study explores a novel method to combat the Light and Elevated Temperature‐Induced Degradation (LeTID) in solar cell modules, which significantly reduces their efficiency and lifespan. This method involves applying alternating current (AC) of various waveforms (triangular, sinusoidal, and square) and frequencies (5 and 100 kHz) to boron‐doped p‐type passivated emitter rear contact (p‐PERC) solar cell modules. This approach effectively lowers the series resistance at the critical junction between the silver (Ag) contact and the silicon emitter layer of the PERC solar cell, thereby reducing charge recombination hindered by high resistance, especially at elevated temperatures. As a result, there is an improved flow of electrical charges, leading to decreased energy loss and increased solar cell efficiency. The study's findings indicate that a slow, smooth sinusoidal AC waveform at 100 kHz is particularly effective, restoring about 100% of the original performance of the panel. Moreover, oscillations at 5 kHz also show considerable efficacy, recovering more than 96% of the performance. The sinusoidal waveform is noted to surpass both triangular and square waveforms in recovery efficiency. This research highlights the use of high‐frequency AC electricity as a viable strategy to extend the lifespan and enhance the performance of solar panels.

Suppressing The Blistering of Silicon Nitride in PERC Solar Cells for High Industrial Yield

Passivated emitter and rear contact (PERC) solar cells possess the highest photovoltaic market share at present. In industrial production, blistering of the rear silicon nitride (SiNx) passivation layer significantly affects the yield. In order to solve this problem, the relevant processes for manufacturing the PERC solar cells have been carefully studied. It was found that polishing of the silicon wafer rear surface, aluminum (AlOx) thickness, and the deposition process of the SiNx layer will affect the blistering ratio. By optimizing the manufacturing process mentioned above, the blistering ratio of the PERC solar cells has been effectively suppressed. This work not only provides reliable technical support for the yield improvement of the PERC solar cells but also provides some useful reference for the tunnel oxide passivated contact (TOPcon) and back contact (BC) solar cell industrial manufacture.

Laser ablation of thin SiN x layer coated on silicon wafer—evaluation of process performance for PERC solar cell application

In fabricating passivated emitter and rear contact (PERC) solar cells, creating small openings on the SiN x coated silicon substrate to establish metal contacts necessitates using a nanosecond pulsed green laser for ablation. However, the thermal nature of laser ablation poses a challenge. Excessive nitrogen diffusion from SiN x into the silicon substrate can compromise the electrical performance of solar cells. Therefore, this study aims to comprehensively understand how laser parameters impact the electrical properties of such solar cells. PERC solar cell precursors were initially fabricated by ablating the SiN x layer at four laser fluences, each corresponding to different regimes: solid, liquid, vapor, and phase explosion. Subsequently, various optical, chemical, and electrical characterizations were conducted on the solar cell precursors. Complete PERC solar cells were also fabricated to measure quantum efficiency (QE). In the solid regime, SiN x removal is precise, with minimal thermal damage, resulting in a nitrogen concentration of approximately 0.15%. Photoluminescence count and carrier lifetime are notably higher by 21% in the solid regime compared to the explosive regime. The QE measurement at 984 nm quantitatively assesses rear-side recombination losses. Notably, 26% of the area exhibits a 56% QE in the solid state, while this number drops to around 22% in the explosive state. This decline can be attributed to increased thermal damage in the explosive regime, which augments recombination centers and diminishes the solar cell performance. PERC solar cells ablated in the solid regime showcase lower subsurface damage, superior electrical characteristics, and higher performance than those ablated in the explosive regime.

Comparative Study on Energy Yield of Tunnel Oxide Passivated Contact (TOPCon) and Passivated Emitter and Rear Contact (PERC) Solar Cells and Analysis of Optimal Installation Method for Vertical Photovoltaics

Photovoltaic (PV) installations have traditionally relied on a conventional south-facing orientation, which maximizes energy production at noon but has lower energy generation in the morning and afternoon. Vertical photovoltaic (VPV) systems have emerged as promising alternatives to address this inconsistency. Vertical photovoltaic systems can enhance energy generation by facing east in the morning and west in the afternoon. We compared the performance of n-tunnel oxide passivated contact (n-TOPCon) and p-passivated emitter and rear contact (p-PERC) cells in vertical photovoltaic systems to determine whether the optimal installation direction of bifacial vertical photovoltaics is east or west. Our findings indicated that n-TOPCon cells exhibited higher energy yields than p-PERC cells, with a difference of approximately 8%, attributed to the superior bifaciality and lower temperature coefficient of power of n-TOPCon. Additionally, the energy yield was higher for n-TOPCon modules when the front faced east, whereas the PERC modules performed better with a west-facing front. This contributes to the knowledge of the factors for energy production in vertical photovoltaic systems and the optimization of installation configurations.

Hydrogen Sulfide Passivation for p-Type Passivated Emitter and Rear Contact Solar Cells

Hydrogen Sulfide Passivation for p-Type Passivated Emitter and Rear Contact Solar Cells

Performance Assessment of Cell-Separation Processes for Rear-Contact Solar Cells: Comparison of Indoor and Outdoor Measurements

Half-cell and third-cell modules are the current module technology standard due to their enhanced electrical performance. Also, special module layouts for building or vehicle integrated photovoltaics rely on non-standard cell formats obtained by separation techniques. For either application, interdigitated back-contact (IBC) solar cells are one of the promising cell technologies due to their higher performance and more aesthetic appearance. Thus, a cell separation process, usually employing laser tools, is needed that splits the cells as partial cells are manufactured from full cells. However, this cell cutting also induces additional electrical losses. In this work, we analyze the performance of third cell mini-modules made of IBC cells in comparison to PERC cells as reference. Under standard test conditions (STC), an overall performance gain can only be found for the PERC cells, while current and recombination losses dominate the IBC mini-modules. Outdoor measurements under non-STC conditions reveal reduced performance gains under lower illumination. We show a detailed analysis regarding the performance differences of the IBC and PERC cell technologies at indoor STC and outdoor non-STC test conditions.

Maskless fabrication of quasi-omnidirectional V-groove solar cells using an alkaline solution-based method

Silicon passivated emitter and rear contact (PERC) solar cells with V-groove texture were fabricated using maskless alkaline solution etching with in-house developed additive. Compared with the traditional pyramid texture, the V-groove texture possesses superior effective minority carrier lifetime, enhanced p–n junction quality and better applied filling factor (FF). In addition, a V-groove texture can greatly reduce the shading area and edge damage of front Ag electrodes when the V-groove direction is parallel to the gridline electrodes. Due to these factors, the V-groove solar cells have a higher efficiency (21.78%) than pyramid solar cells (21.62%). Interestingly, external quantum efficiency (EQE) and reflectance of the V-groove solar cells exhibit a slight decrease when the incident light angle (θ) is increased from 0° to 75°, which confirms the excellent quasi omnidirectionality of the V-groove solar cells. The proposed V-groove solar cell design shows a 2.84% relative enhancement of energy output over traditional pyramid solar cells.

The Mechanism of Hot Spots Caused by Avalanche Breakdown in Gallium-Doped PERC Solar Cells

Gallium-doped p-type passivated emitter and rear contact (PERC) solar cells, which eliminate light-induced degradation (LID) and reduce the impact of light- and elevated-temperature-induced degradation (LeTID), have completely replaced boron-doped p-type PERC cells. However, in previous experiments, we found hot spots in the center of gallium-doped PERC solar cells. In this study, it was found that gallium-doped PERC cells had uneven resistivity, which caused hot spots brought about by the avalanche breakdown of PN junctions. There were significant hot spots in the center of the tested cells, with an average resistivity of 0.4–0.5 Ωcm and nonuniformity greater than 30%, or at an average resistivity of 0.5–0.6 Ωcm with nonuniformity greater than 40%. In this paper we describe and study in detail hot spots triggered by the uneven resistivity of gallium-doped cells and analyze the causes and related influencing factors, thereby providing guidance and a reference for the improvement of the performance and reliability of gallium-doped PERC solar cells.

An experimental study on laser ablation of Ultra-thin SiNx layer of PERC solar cell

In this work, a nanosecond green laser (532 nm) is used to generate narrow openings by removing an ultra-thin (85 nm) SiN x layer that is coated on a silicon substrate for application in the fabrication of Passivated Emitter and Rear Contact (PERC) solar cells. An experimental analysis is presented to identify the optimal range of laser parameters for an efficient ablation with minimal damage to the silicon substrate. The ablated samples were characterized using a 3D profilometer to obtain the surface profiles and scanning electron microscope imaging to observe the surface quality. Further, energy-dispersive X-ray line analysis and atom probe tomography were performed to evaluate the nitrogen content on the surface and along the depth, respectively. The experimental results suggest that the SiN x layer starts to ablate only above a threshold laser fluence of 1.4 J/cm2, while the surface bulged out for laser fluence slightly below the ablation threshold. The central part of the ablated region was clean with a negligible nitrogen concentration at the surface, about ∼0.03% at a fluence of 2.4 J/cm2. Nitrogen concentration reduces continuously and almost becomes zero at 80 nm depth, suggesting complete ablation of the SiN x layer for establishing electrical contacts. The ablation width was close to the laser spot diameter only at lower values of the laser fluence. The lowest value of ablation depth was about 180 nm, suggesting that only about 95 nm layer of the silicon is ablated. The study demonstrates that nanosecond laser ablation is a potential technique for ablation of the SiN x layer of PERC solar cells but requires choosing the optimal parameters.

Chemical stoichiometry effect of hafnium oxide (HfOx) for passivation layer of PERC solar cells

Hafnium oxide (HfOx) is being investigated as a new candidate for the passivation layer of silicon solar cells due to its excellent electrical and optical properties, such as high dielectric constant, large band gap, refractive index, high transparency, and thermodynamic stability in contact with Si. In this paper, the HfOx is analyzed for novel material applied to the passivation layer to improve the performance of passivated emitter and rear contact (PERC) solar cells. For optimisation of the passivation layer of the PERC solar cell, chemical stoichiometry and passivation properties such as interface trap density, fixed charge and effective carrier lifetime are studied before and after the annealing process. After annealing in O2, interface trap density (Dit) decreased from 8.15 × 1010 eV−1cm−2 to 2.37 × 1010 eV−1cm−2 and the fixed charge (Qf) changed from positive to negative after annealing due to the reduction of oxygen vacancies. However, the passivation properties did not meet expectations due to blistering after annealing at 500 °C or higher and the highest effective carrier lifetime was 188.56 μs after annealing at 400 °C, which was improved from 49.48 μs before annealing. It was confirmed that improved passivation performance and solar cell efficiency could be achieved through the chemical stoichiometry effect by a simple annealing process.

Losses in bifacial PERC solar cell due to rear grid design and scope of improvement

Photovoltaic (PV) industries are continuously trying to improve the module performance with the adoption of newer cell technologies. Recently, bifacial passivated emitter rear contact (PERC) solar cell technology has entered the market to further improve the module performance through the absorption of the extra photons reflected from the background. This work is mainly focused on optimizing the rear side grid pattern of the bifacial PERC solar cells for improvement of the total output power gain. We have developed an analytical model based on the front and rear grid pattern of commercially available bifacial PERC solar cells to calculate the optical shading and electrical losses for both sides of the solar cells. It is perceived that the rear shading loss due to rear grid design of industrial bifacial PERC solar cells is very high (∼30%) as compared to the front side (∼5%) of the cells. The model calculation shows that if with the improved laser scribing technology the finger width of the rear grid pattern be drastically reduced from ∼ 200 μm (measured value) to 25 μm the optical shading loss may be minimized to 11–14% from 30% without compromising the effective busbar resistance.

Reaction Kinetics Analysis of Treatment Process on Light-Induced Degradation for p-Type Passivated Emitter and Rear Contact Solar Cell Module with Gallium Cz-Si Wafer

The light-induced degradation (LID) phenomenon in solar cells reduces power generation output. Previously, a method was developed to prevent LID where a group III impurity that can replace boron is added to the silicon wafer. However, in a subsequent study, performance degradation was observed in gallium-doped solar wafers and cells, and a degradation pattern similar to that occurring in light and elevated temperature-induced degradation (LeTID) was reported. In this study, a 72-cell module was fabricated using gallium-doped PERC cells, and the treatment of the LID process for carrier injection in the range of 1 to 7 A at 130 °C was analyzed using kinetic theory. We selectively heated only the solar cells inside a 72-cell module using a half-bridge resonance circuit for remote heating. To monitor the treatment of LID process in real time, a custom multimeter manufactured using an ACS758 current sensor and a microcomputer was used. Least-squares curve fitting was performed on the measured data using a reaction kinetics model. When the carrier-injection condition was applied to the gallium-doped PERC solar cell module at a temperature of 130 °C, the observed degradation and treatment pattern were similar to LeTID. We assumed that the treatment rate would increase as the size of the injected carrier increased; however, the 5 A condition exhibited the fastest treatment rate. It was deduced that the major factors of change in the overall treatment of the LID process vary depending on the rate of conversion from the LID state to the treatment state. In conclusion, it can be expected that the deterioration state of the gallium-doped solar cell module changes due to the treatment rate that varies depending on the carrier-injection conditions.

Ultrafast Random‐Pyramid Texturing for Efficient Monocrystalline Silicon Solar Cells

Herein, an ultrafast random‐pyramid texturing process is proposed for monocrystalline silicon (mono‐Si) solar cells by combining metal‐catalyzed chemical etching (MCCE) and the standard alkaline texturing process. Namely, large numbers of artificial defects are introduced on the wafer surface in 3 min by MCCE; therefore, the process duration of alkaline texturing is largely shortened from 420 s for the as‐cut wafer to 180 s for the wafer with artificial defects due to its high surface reactivity. Moreover, those tiny artificial defects are apt to form small pyramids, resulting in a better light‐trapping performance. As a demonstration, the passivated emitter rear contact solar cell with ultrafast random pyramid texture achieves a power conversion efficiency of 23.02%. Therefore, such a cost‐effective ultrafast texturing strategy can open a promising new route toward the mass production of high‐efficiency industrial mono‐Si solar cells.

Damp‐heat induced degradation in photovoltaic modules manufactured with passivated emitter and rear contact solar cells

AbstractCorrosion is one of the main PV module failure mechanisms, as it can cause severe electrical performance degradation in PV modules exposed to hot and humid environments. Moisture penetrating a photovoltaic (PV) module may react with the metallic components causing corrosion. In addition, acetic acid which is produced by hydrolysis of ethylene vinyl acetate (EVA), the most common encapsulant, may further degrade metallic components. Corrosion is one of the main PV module failure mechanisms, as it can cause severe electrical performance degradation in PV modules exposed to hot and humid environments. The specific chemical reactions involved in the corrosion mechanisms for the different components are well understood. However, which of these causes the most serious degradation in the field, and therefore, most severe power loss is unknown. Moreover, the severity of corrosion in the absence of acetic acid is not yet well researched. This work distinguished between the front and rear side corrosion mechanisms and identified the different electrical signatures observed due to them. The experiment included damp‐heat (DH) conditioning of single‐cell mini‐modules, containing passivated emitter and rear contact (PERC) solar cells, laminated with a polyethylene terephthalate (PET) based backsheet. Furthermore, half‐encapsulated PERC PV cells were tested, with either the front or the rear side exposed. Electrical and material characterisation were conducted for the investigation of the sample degradation, and the performance decrease, related to the degradation of the rear surface passivation, was examined.

Optoelectrical analysis of TCO+Silicon oxide double layers at the front and rear side of silicon heterojunction solar cells

Silicon Heterojunction has become a promising technology to substitute passivated emitter and rear contact (PERC) solar cells in pursuance of lower levelized cost of electricity through high efficiency devices. While high open circuit voltages and fill factors are reached, current loss related to the front and rear contacts, such as the transparent conductive oxide (TCO) layers is still a limiting factor to come closer to the efficiency limit of silicon based solar cells. Furthermore, reducing indium consumption for the TCO has become mandatory to push silicon heterojunction technology towards a terawatt scale production due to material scarcity and costs. To address these issues dielectric layers, such as silicon dioxide or nitride cappings are implemented to reduce TCO thicknesses both diminishing parasitic absorption and material consumption. However, reducing the TCO thickness comes in cost of resistive losses. Furthermore, the TCO properties do vary with thickness and neighboring layer configuration altering the optimization frame of the device. In this paper we present a detailed analysis to quantify the optoelectrical losses trade-off associated to the TCO thickness reduction in such layer stacks. Through the analysis we show and explain why experimental bifacial cells with 20 nm front and rear TCO perform at a similar level to reference cells with 75 nm under front and rear illumination reaching efficiency close to 24% at 92% bifaciality. We present as well a simple interconnection method via screen printing metallization to implement a thin TCO/silicon dioxide/silver reflector enhancing current density from 39.6 to 40.4 mA/cm 2 without compromising resistive losses resulting in a 0.2% absolute solar cell efficiency increase from a bifacial design (23.5–23.7%). Finally, following this approach we present a certified champion cell with an efficiency of 24.6%. • Analysis of TCO variations on electron and hole contact for Si heterojunction solar cells by simulations and experiments. • Both sides 20 nm TCO + SiO 2 layer stack SHJ solar cells with 23.9% efficiency. • Champion solar cell with rear 20 nm TCO + SiO 2 layer stack and silver rear reflector with 24.6% efficiency.

N-TOPCon 태양전지의 선택적 에미터 형성 기술 분석

The main efficiency limiting factors for homogeneous emitter solar cells are resistance loss through metal contact on the front side and recombination loss at the surface. Herein, a selective emitter technology is introduced to solve the above problem, and it is currently commercialized in the mainstream p-PERC (Passivated Emitter Rear Contact) solar cell. The selective emitter boosts efficiency by 0.3~0.4% when compared to a homogeneous emitter, and when applied to the n-TOPCon (Tunnel Oxide Passivated Contact) solar cell, high efficiency of 26% or higher may be predicted. The most widely utilized selective emitter technologies are laser and etch-back. The One-Step Technology, which is suited to the n-TOPCon solar cell process, a laser is suitable for mass manufacturing with high yield. Because selective emitters increase electrical characteristics, which impact cell efficiency, it is required to study and create a technology that is optimal for the n-TOPCon manufacturing process.

One-step preparation of TiO2 anti-reflection coating and cover layer by liquid phase deposition for monocrystalline Si PERC solar cell

This study proposed a one-step liquid phase deposition (LPD) technique to fabricate a front-side anti-reflective coating (ARC) and rear-side cover layer for a passivated emitter and rear cell solar cell. The production process involves the deposition of TiO 2 thin film by using a (NH 4 ) 2 TiF 6 and H 3 BO 3 mixture in a liquid phase filter and cycling deposition system, in which H 3 BO 3 concentration influences the TiO 2 thin film deposition rate, the Ti x Si 1-x O y interfacial layer thickness, and thin film quality. The proposed technique is a one-step, uniform, and large-scale double-sided coating batch process viable for non-vacuum environments, thus enabling a simple manufacturing process and requiring low equipment costs. The fabricated LPD-TiO 2 thin film demonstrated ASTM 5B adhesion and 3.3% uniformity. The technique involves the use of a 0.2 M (NH 4 ) 2 TiF 6 and 0.5 M H 3 BO 3 mixture for deposition under 50 °C to deposit a 68-nm-thick LPD-TiO 2 thin film on pyramid Si wafer. The average reflectance and transmittance of the thin film at 400–800 nm wavelength was 2.7% and 96.5%, respectively. Passivated emitter and rear contact solar cells prepared using the proposed LPD-TiO 2 coating technique demonstrated the following outstanding properties: 9.8 A short-circuit current, 0.68 V open circuit voltage, 81.0% fill factor, and 21.3% photoelectric conversion efficiency (η). The proposed technique demonstrates high potential for use in the low-cost manufacturing of silicon solar cells. • Passivated emitter and rear contact (PERC) solar cells are fabricated. • Front-side anti-reflective and back-side cover layers are prepared in one step. • Low cost and batch-type of TiO 2 films are made by liquid phase deposition (LPD). • PERC solar cell with the LPD functional films shows the better characteristics. • LPD-TiO 2 functional films are favorable for high performance PERC solar cells.

Q CELLS > 24% Silicon Solar Cells With Mass-Production Processes

Within the last years, Q CELLS has developed a silicon solar cell structure yielding an energy conversion efficiency exceeding 24%. The cell structure features a so-called passivating contact consisting of an interfacial oxide and an n-type polysilicon layer on the rear side, double-sided screen-printed metal contacts, a module-optimized anti-reflective coating, a homogeneous front-side emitter, and an n-type silicon substrate. For the fabrication of this type of solar cell, a lean processing sequence has been applied by using exclusively mass-production processes in Q CELLS’ pilot R&D line in Thalheim, Germany. For module integration, state-of-the-art technology, such as half-cells, multi-wire interconnection, standard encapsulants, and zero-gap technology, can be applied. Hence, this solar cell structure has the potential to fully close the small remaining gap to the highest efficiency cell technologies, such as heterojunction and rear-contact solar cells at very competitive manufacturing cost. In analogy to Q CELLS' PERC-like Q.ANTUM technology, and in contrast to conventional passivated emitter and rear cells (PERC), this novel solar cell is shown to reliably suppress light-induced degradation.

A novel passivating electron contact for high-performance silicon solar cells by ALD Al-doped TiO2

Titanium oxide (TiO2) thin film has attracted wide interest in high-efficiency silicon solar cells as an electron selective contact due to its low conduction band offset with silicon and an excellent level of passivation, while the incorporation of a small amount of dopants is also expected to improve the performance of thin films. In this work, assisted with density functional theory (DFT) modelling, we study the electronic band structure of aluminum (Al)-doped TiO2 (ATO). The atomic-layer-deposited (ALD) ATO thin films are successfully prepared, and the elemental analysis, passivation effect, thermal stability, conductivity and optical properties of the ATO are systematically investigated. An ultra-high effective minority carrier lifetime (τeff) of 1.9 ms and a low contact resistivity (ρc) of 0.1 Ω·cm2 are simultaneously achieved on silicon wafers. Meanwhile, it is found that the ATO thin films possess better thermal stability than the TiO2 thin film. Finally, a large-area (118.7 × 100 mm2) p-type passivated emitter and rear contact (PERC) solar cells integrated with an ALD ATO layer on the illumination side was fabricated, and a champion efficiency of 21.4% was achieved with an optimal Al concentration in ATO, which is significantly higher than a PERC solar cell with intrinsic TiO2. This work shows ATO a very attractive alternative achieving high-efficiency crystalline silicon solar cells.

Evaluation of dominant loss mechanisms of PERC cells for optimization of rear passivating stacks

In this paper a comprehensive theoretical analysis has been carried out for Passivated Emitter Rear Contact (PERC) solar cells with the help of numerical modeling using Sentaurus TCAD simulation software. For the rear passivation we have explored various dielectric layers, such as, Aluminium Oxide (Al2O3), Silicon Oxide (SiO2), Hafnium Oxide (HfO2) and Aluminium Nitride (AlN) along with the Silicon Nitride (SiNx) capping layer. Optical generation near the rear side the passivating stacks was analyzed. Recombination current densities were also evaluated for assorted defects with various concentration, hole and electron capture cross sections and position of quasi Fermi level for surface passivation. Thicknesses of the passivating and capping layers were optimized with respect to optical and electrical losses. Field effect passivation (FEP) property of the rear passivating stacks was also investigated. For simulated textured Al-BSF solar cell on silicon wafer of bulk lifetime 250µs, an efficiency of 19.5% was obtained. This solar cell has been used here for reference. We have achieved efficiency of 22.6% for PERC solar cells of rear contact area of 8% on similar type of wafer. It was noticed from few articles that industrial PERC solar cells were fabricated using rear metal contact less than 10% which is well validating our study. It was also perceived that employing Passivated Emitter Rear Totally Diffused (PERT) structure with optimized design parameters further improved the efficiency to ∼ 24%.