Fabrication Of Silicon Solar Cells Research Articles

Exploring low temperature-sputtered indium tin oxide (ITO) as an anti-reflection layer for silicon solar cells

Abstract This paper tackles challenges in silicon (Si) solar cells, specifically the use of hazardous Phosphorus Oxychloride (POCl3) for emitter formation and silane/ammonia for the Anti-Reflective Coating (ARC) layer, accompanied by high-temperature metallization. The study proposes an eco-friendly ARC layer process, replacing toxic materials. Indium Tin Oxide (ITO) with a refractive index of ~2.0 is suggested as a non-toxic substitute for SiNx in the ARC layer. ITO enables fine-tuning of optical parameters and, with its electrical properties, supports low-resistivity contacts through efficient, low-temperature metallization processes. ITO-passivated solar cells with Ag polymer paste as a front contact exhibit promising characteristics: a commendable photocurrent density (Jsc) of 20 mA/cm2 at 850°C, low series resistance (Rs) of 1.9 Ω, and high shunt resistance (Rshunt) of 28.9 Ω, as demonstrated by illuminated I-V measurements. Implementing ITO as the ARC on a less toxic emitter junction enhances Si solar cells current density gain, minimizing current leakage during high-temperature processing. In conclusion, adopting less toxic materials and employing low-temperature processing in passive silicon solar cell fabrication present an attractive alternative for cost reduction and contribute to environmentally sustainable practices in green manufacturing.

Controllable Fabrication of Silicon Solar Cells with Inverted or Upright Pyramid Structures by a One-Step Copper Catalysis Method

Silicon has garnered significant attention as the primary material for solar cell preparation. Traditional alkaline etching solutions are limited to creating an upright pyramid structure on monocrystalline silicon surfaces. However, research indicates that an inverted pyramid structure exhibits superior light-trapping properties compared to the upright pyramid structure. In this study, we employed a one-step copper ion metal-assisted chemical etching process to fabricate an inverted pyramid structure on monocrystalline silicon wafers. This method allows for the customization of either inverted or upright pyramid structures by adjusting the concentration of specific solution components. Characterization of the textured silicon wafers reveals that the inverted pyramid structure exhibits lower reflectivity than both the upright pyramid structure and polished silicon. By integrating this texturing technique into the solar cell production line, we successfully produced solar cells with both inverted and upright pyramid structures. Evaluation of various solar cell parameters demonstrates that the inverted pyramid structure outperforms the upright pyramid structure, showcasing lower reflectivity and higher photoelectric conversion efficiency.

Photovoltaic Manufacturing Factories and Industrial Site Environmental Impact Assessment

Life cycle inventories (LCIs) and life cycle assessments (LCAs) of photovoltaic (PV) modules and their components focus on the operations of PV factories, but the factories and industrial site product and construction stages are either not or only partially tackled. This work contributes through the bottom-up, model-based generation of LCIs and LCAs for setting up a vertically integrated 5 GWp/a PV industrial site, including the manufacturing of silicon ingots, wafers, solar cells, and PV modules, on a 50 ha greenfield location. Two comparative LCAs are performed. The first compares the annualized environmental impacts of the developed LCI sets with four existing inventories in the Ecoinvent v3.8 database. The second comparative LCA explores the environmental impact differences concerning the industrial site when using different building systems for the factories. Here, the reference system with a steel structure is compared with two alternative building systems: precast concrete and structural timber. The results show that the wafer, cell, and module factories’ annualized environmental impacts with the Ecoinvent LCIs are strongly overestimated. For the ingot factory, the opposite result is identified. The impacts of all four factories show reductions of between 11.7% and 94.3% for 14 of the 15 impact categories. High mean environmental impact shares of 79.0%, 78.2% and 79.2% for the steel, precast concrete and timber structural building systems, respectively, are generated at the product stage. The process and facilities equipment generates 54.2%, 54.4% and 58.2% of the total product and construction stages’ mean environmental impact shares. The proposed alternative timber building system reduces the environmental impacts in 14 of the 15 evaluated categories, with reductions ranging from 1.1% to 12.4%.

Influence of inverted pyramid texturization on front metallization and performance of crystalline silicon solar cells

The silicon surface texturing is an essential part for the fabrication of crystalline silicon solar cells to increase the conversion efficiency. By adjusting the etching texturing condition, inverted pyramid (IP) and upright pyramid (UP) texturization were prepared on crystalline silicon substrates for fabrication of PERC solar cells. The surface morphology not only affects the light trapping but also impacts electrode shading loss and front electrode contact interface. The IP texturization presents better anti-reflective performance due to more common light paths and narrower silver grids owing to less flow of Ag paste on concave blocked structure, both of which results in the higher short-circuit current density (Jsc). Yet in terms of front Ag/Si contact interface, the IP texturization causes more Ag crystallites and more surface recombination under the present condition suitable for UP texturization because of more edges on the upper part of IP, which leads to the lower open-circuit voltage (Voc). The final conversion efficiency of IP solar cells (23.61 %) is 0.06 % higher than that of UP solar cells (23.55 %). An improvement about 0.07 mA/cm2 of Jsc was achieved with IP samples and Voc has a decrease of 0.3 mV caused by the surface recombination on IP texturization. In summary, the structural characteristics of IP results in lower reflectivity and less electrode shading, while Ag/Si contact interface could be optimized by adjusting the processing condition, ultimately promising the higher efficiency.

Silicon Solar Cells: Trends, Manufacturing Challenges, and AI Perspectives

Photovoltaic (PV) installations have experienced significant growth in the past 20 years. During this period, the solar industry has witnessed technological advances, cost reductions, and increased awareness of renewable energy’s benefits. As more than 90% of the commercial solar cells in the market are made from silicon, in this work we will focus on silicon-based solar cells. As PV research is a very dynamic field, we believe that there is a need to present an overview of the status of silicon solar cell manufacturing (from feedstock production to ingot processing to solar cell fabrication), including recycling and the use of artificial intelligence. Therefore, this work introduces the silicon solar cell value chain with cost and sustainability aspects. It provides an overview of the main manufacturing techniques for silicon ingots, specifically Czochralski and directional solidification, with a focus on highlighting their key characteristics. We discuss the major challenges in silicon ingot production for solar applications, particularly optimizing production yield, reducing costs, and improving efficiency to meet the continued high demand for solar cells. We review solar cell technology developments in recent years and the new trends. We briefly discuss the recycling aspects, and finally, we present how digitalization and artificial intelligence can aid in solving some of the current PV industry challenges.

Wet chemical poly-Si(n) wrap-around removal for TOPCon solar cells

This work gives an overview on different technological solutions for polysilicon removal in industrial tunnel oxide passivated contact (i-TOPCon) n-type silicon solar cell fabrication. The removal of parasitically deposited poly-Si layers on the front and the edges is a mandatory requirement for a low reverse bias junction leakage current (Irev). A polysilicon removal study on wafer level shows (i) that the efficient removal of the surface oxide layer before poly-Si etching is crucial to achieve short etching times and (ii) that an additive in the KOH solution enhances etching selectivity between poly-Si and silicon oxide surfaces. To evaluate the impact on device level, TOPCon cells have been fabricated in parallel using in-situ n-doped PECVD and LPCVD layers, as well as ex-situ LPCVD poly-Si layers, with another variation of poly-Si removal processes, namely wet chemical inline, wet chemical batch cluster and atmospheric dry etching (ADE). Our results show that a two-minute inline polysilicon removal in hot KOH meets the Irev qualification in case of as deposited in-situ doped layers, whereas for ex-situ doped layers a batch process with a five-minute KOH etching time is needed. LPCVD poly-Si cells show efficiencies above 23%, PECVD poly-Si cells with a batch cluster poly-Si removal process up to 23.4%.

Overcoming Throughput Limitations of Laser Systems in Solar Cell Manufacturing via On‐The‐Fly Processing Using Polygon Scanners

In this paper, a high‐throughput on‐the‐fly laser processing system for the manufacture of silicon solar cells is proposed. Industrial laser processing machines are systematically limited in a trade‐off between throughput and focal spot size. Additionally, today's laser power and repetition rates cannot be fully utilized because of limited galvanometer scan speeds. This work aims to overcome this using a polygon scanner in an on‐the‐fly laser processing operation. Unlike conventional approaches, this setup does not use high‐precision positioning systems, but reduces wafer transport to a simple conveyor belt to optimize system cost, space, integrability, and cycle rate. The concept is implemented in a demonstrator setup. Applying a laser contact opening process, a throughput of 10 000 wafers per hour is demonstrated. A potential throughput of 13400 wafers per hour is calculated, considering the utilization of more powerful lasers. Inaccuracies due to the unevenness of the surface as well as transport speed oscillations are analyzed and shown not to have an impact on the efficiency of the cells processed with this setup. The throughput is increased five times compared to the theoretical upper‐throughput limitation for the same structure processed by a galvanometer‐driven laser system.

Characterization of tunnel oxide passivated contact fabricated by sputtering and ion implantation technique

Tunnel oxide passivated contact (TOPCon) structures using highly doped n-type polycrystalline silicon were fabricated using facing target sputtering and ion implantation techniques for a SiH4-free fabrication process of high-efficiency silicon solar cells. We investigated the structural and electrical properties of the highly doped n-type poly-Si layers to optimize the ion implantation process. We also investigated the surface passivation quality of our TOPCon structure. An effective carrier lifetime of 2.01 ms and an implied open circuit voltage of 704 mV were obtained for our sample annealed at 950 °C. The sample also exhibits a low contact resistance of 3.22 × 10−3 Ω cm−2. Our results open the way for SiH4-free fabrication of silicon solar cells with a TOPCon structure.

Editorial: Passivating contact solar cells

In the last decade, significant attention has been given to the concept of passivating contact solar cells. Such cells are characterised by very low contact recombination and low contact resistance, a combination that is challenging to achieve with conventional diffused silicon layers. These cells demonstrate a very high open-circuit voltage and therefore higher efficiency. Passivating contacts can be classified into three main technologies according to the material used for the charge-carrier selection: (i) doped amorphous silicon; (ii) doped polycrystalline silicon; and (iii) metal compounds and organic materials. Due to the impressive progress of passivating contacts and the wide variety of technologies and approaches, Progress in Photovoltaic decided to dedicate an entire issue to reviewing the status of this concept. The issue starts with a review of the three main technologies of passivating contacts, summarising their current efficiencies and discussing their distinctive features, advantages, and limitations. While doped amorphous silicon has been used for the manufacturing of industrial heterojunction solar cells for decades, polycrystalline silicon-based solar cells have only recently entered mass production. Interestingly, this technology was introduced to bipolar transistors as early as the 1970s and adapted into silicon solar cells in the 1980s. However, because some aspects other than the contacts limited the obtainable solar cell efficiencies, this technology was not actively investigated until 2013. Nevertheless, since then, a substantial amount of research has been done by several research institutes and companies, enhancing the performance of polycrystalline silicon-based solar cells to efficiencies above 26%. More importantly, significant effort has been made to commercialise this technology with significant progress already reported by several photovoltaic companies. As doped polycrystalline silicon seems to be the most mature passivating contact technology, we review the status of the three leading approaches: The POLO of ISFH, the TOPCon of Fraunhofer ISE, and the monoPoly of SERIS. With several large manufacturers announcing their plans to transfer polycrystalline silicon-based technology into mass production, we also review the activities that have been taken to push the boundaries of this technology and enabled its integration into existing production lines. Manufacturing options, as well as necessary technological advances in cell metallisation and module integration, are discussed from the industrial perspective. We then review the progress of passivating contact technologies that employ metal compounds as the carrier-selective layer. The interest in this technology has recently increased with a few promising families of materials having demonstrated excellent results, specifically alkali/alkaline-earth metal compounds and transition-metal oxides. The number of successful demonstrations of selective-contact materials within these families is increasing fast, with the best solar cell efficiencies now exceeding 23%. The challenges of this technology to be considered for industrial adoption are then discussed, together with its prospects in the context of silicon photovoltaics. In a separate paper, we provide a detailed techno-economic analysis of the use of atomic layer deposited transition-metal oxides for the fabrication of silicon solar cells. The special issue concludes with a paper discussing the challenges and opportunities in the metallisation of industrial perovskite/silicon tandem solar cells. We want to thank all the authors for their great contributions. It was a pleasure to work with such a talented and diverse group of researchers. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

Monolithic Perovskite/Silicon Tandems with >28% Efficiency: Role of Silicon‐Surface Texture on Perovskite Properties

AbstractTextured silicon wafers used in silicon solar cell manufacturing offer superior light trapping, which is a critical enabler for high‐performance photovoltaics. A similar optical benefit can be obtained in monolithic perovskite/silicon tandem solar cells, enhancing the current output of the silicon bottom cell. Yet, such complex silicon surfaces may affect the structural and optoelectronic properties of the overlying perovskite films. Here, through extensive characterization based on optical and microstructural spectroscopy, it is found that the main effect of such substrate morphology lies in an altering of the photoluminescence response of the perovskite, which is associated with thickness variations of the perovskite, rather than lattice strain or compositional changes. With this understanding, the design of high‐performance perovskite/silicon tandems is rationalized, yielding certified power conversion efficiencies of >28%.

Past, Present, and Future Outlook for Edge Isolation Processes in Highly Efficient Silicon Solar Cell Manufacturing

This work highlights present research and mass production results of wet‐chemical solutions for industrial edge isolation of silicon solar cells, aiming for a reduction of nitric acid consumption and production costs as well as a simultaneous increase in efficiency. All processes are applied to either industrially passivated emitter and rear contact (PERC) or tunnel oxide‐passivated contact (TOPCon) solar cells. Herein, a review of different edge isolation techniques in the history of silicon solar cell processing is presented. Subsequently, novel wet‐chemical approaches are focused on, namely 1) HNO3‐reduced edge isolation (InOxSide Fusion), 2) HNO3‐free edge isolation (InOxSide Blue), and 3) batch cluster solution—a combination of an acidic inline and an alkaline batch tool for emitter edge isolation of PERC and TOPCon solar cells. For each of the approaches, cell results and total cost of ownership estimations are presented. Based on all findings, a comprehensive discussion between inline versus batch‐cluster processing is presented. All investigations are performed on industrial equipment, wafer sizes, and a solar cell efficiency level of above 23%.

Screen-printed contacts for crystalline silicon solar cells: an overview

Over the years, the photovoltaic market, worldwide, has been witnessing a double-digit growth rate. The silicon solar cell manufacturing technology has evolved to utilize raw materials optimally to address this growth. One of the ways in which manufacturers are addressing the challenge is by increasing the cell size and making thinner wafers. With this change in parameters, understanding the metal contact formation in solar cells becomes paramount to improve their efficiency. Screen printing is a widely used method to form metal contacts on solar cells and is ideally suited for large-volume manufacturing. This paper presents a review of the (a) role of screen printing in various solar cell architectures and (b) existing models for current conduction and contact formation mechanisms. An alternate approach to current conduction and contact formation mechanism in silicon solar cells is proposed.

Screen Printable Sol-Gel Materials for High-Throughput Borosilicate Glass Film Production.

The use of sol-gel materials can simplify the industrial fabrication of high-efficiency silicon solar cells if a suitable deposition method is established. In this work, we investigate the possibilities to adapt a borosilicate glass sol-gel to provide a stable screen printing process. This material has previously been used as a boron dopant source for silicon solar cells. We now use an adjusted synthesis process, with an increased gelling time and different additives. This changes the rheological properties (i.e., the elastic and viscous moduli G′ and G″) in a way that avoids the dripping of paste through the screen and that stabilizes the material transfer in subsequent printing steps. Using this synthesis process, we were able to show a printing process with long-term stability of more than 500 prints. When comparing the adjusted to the initial paste, we show that, after thermal treatment, the obtained thin films are very similar in terms of their constitution, with a refractive index between n = 1.47 (initial) and n = 1.55 (adjusted). We also show that they provide the same amount of doping under the tested conditions (950 °C, 30 min), resulting in sheet resistances of R□ = (42.5 ± 2.6) Ω/□ (initial) and R□ = (46.4 ± 3.6) Ω/□ (adjusted).

Sputtered Ultrathin TiO2 as Electron Transport Layer in Silicon Heterojunction Solar Cell Technology.

This work presents the implementation of ultrathin TiO2 films, deposited at room temperature by radio-frequency magnetron sputtering, as electron-selective contacts in silicon heterojunction solar cells. The effect of the working pressure on the properties of the TiO2 layers and its subsequent impact on the main parameters of the device are studied. The material characterization revealed an amorphous structure regardless of the working pressure; a rougher surface; and a blue shift in bandgap in the TiO2 layer deposited at the highest-pressure value of 0.89 Pa. When incorporated as part of the passivated full-area electron contact in silicon heterojunction solar cell, the chemical passivation provided by the intrinsic a-Si:H rapidly deteriorates upon the sputtering of the ultra-thin TiO2 films, although a short anneal is shown to restore much of the passivation lost. The deposition pressure and film thicknesses proved to be critical for the efficiency of the devices. The film thicknesses below 2 nm are necessary to reach open-circuit values above 660 mV, regardless of the deposition pressure. More so, the fill-factor showed a strong dependence on deposition pressure, with the best values obtained for the highest deposition pressure, which we correlated to the porosity of the films. Overall, these results show the potential to fabricate silicon solar cells with a simple implementation of electron-selective TiO2 contact deposited by magnetron sputtering. These results show the potential to fabricate silicon solar cells with a simple implementation of electron-selective TiO2 contact.

Polycrystalline Silicon Membranes for Solar Cells Fabricated Using Water-soluble Sacrificial Layers

During the fabrication of crystalline silicon solar cells, kerf-loss caused by the wire-sawing of silicon ingots to produce thin wafers inevitably limits the reduction of electricity production cost. To avoid the kerf-loss, direct growth of crystalline silicon wafers of 50-150 μm with a porous separation layer that can be mechanically broken during the exfoliation process, has been widely investigated. However, several issues including flattening of the surface after the exfoliation remain unsolved. In this work an alternative method that utilizes a water-soluble Sr3Al2O6 (SAO) sacrificial layer inserted between the mother substrate and the grown crystalline silicon layers is introduced. Polycrystalline silicon layers were grown on SAO/Si by plasma-enhanced CVD process and silicon membranes could be successfully obtained after the dissolution of SAO in the water. Same process could be applied to obtain flexible amorphous silicon membranes. Further research is being conducted to increase the size of the exfoliated wafer, which expects to reduce the production cost of crystalline silicon solar cells effectively.

Fabrication and characterization of silicon solar cells towards improvement of power efficiency

In recent years, natural energy has been increasingly popular as a source of electricity. Silicon-based solar cell devices are employed to harvest the natural energy, which uses the photovoltaic effect to convert sunlight into an electromotive force. Texturing was usually done on the solar cell surface using a variety of ways to improve solar cell efficiency. In this work, an inductively coupled plasma reactive ion etching (ICP-RIE) texturing approach has been adopted. This research also examines the fabrication of crystalline silicon solar cells with and without texturing and characterizes them to quantify the efficiency improvement. All the characterization is performed inside a clean room to support efficient results.

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.

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.

Detection of microcracks and dark spots in monocrystalline PERC cells using photoluminescene imaging and YOLO-based CNN with spatial pyramid pooling

Two common defects encountered during manufacturing of crystalline silicon solar cells are microcrack and dark spot or dark region. The microcrack in particular is a major threat to module performance since it is responsible for most PV failures and other types of damage in the field. On the other hand, dark region in which one cell or part of the cell appears darker under UV illumination is mainly responsible for PV reduced efficiency, and eventually lost of performance. Therefore, one key challenge for solar cell manufacturers is to remove defective cells from further processing. Recently, few researchers have investigated deep learning as an alternative approach for defect detection in solar cell manufacturing. The results are quite encouraging. This paper evaluates the convolutional neural network based on heavy-weighted You Only Look Once (YOLO) version 4 or YOLOv4 and the tiny version of this algorithm referred here as Tiny-YOLOv4. Experimental results suggest that the multi-class YOLOv4 is the best model in term of mean average precision (mAP) and prediction time, averaging at 98.8% and 62.9 ms respectively. Meanwhile an improved Tiny-YOLOv4 with Spatial Pyramid Pooling scheme resulted in mAP of 91.0% and runtime of 28.2 ms. Even though the tiny-weighted YOLOv4 performs slightly lower compared to its heavy-weighted counterpart, however the runtime of the former is 2.2 order much faster than the later.

Structural and Optical Properties of CuO Thin Films Synthesized Using Spray Pyrolysis Method

Copper oxide thin films were obtained using pulsating spray pyrolysis method. The morphological, structural, and optical properties of fabricated films were studied. X-ray analysis revealed that the CuO thin films are single-phase. The study of films morphology by SEM and AFM methods showed that the obtained films have a fairly high surface roughness and contain grains of different shapes and sizes. It was found that the obtained films of copper oxide have high values of the absorption coefficient, which confirms the possibility of their use as absorbing layers for solar cells. The obtained values of the optical band gap of the material are in the range from 1.45 eV to 1.60 eV. Raman spectroscopy revealed three modes A1g, B1g, and B2g, of the crystal structure of monoclinic CuO. The devices based on p-type copper oxide are promising for solar cells fabrication because they can reduce production costs, due to their low cost and inexpensive production methods compared to silicon solar cells fabrication.