Rie-texturing of multicrystalline silicon solar cells (original) (raw)
Plasma-texturization for multicrystalline silicon solar cells
Conference Record of the Twenty-Eighth IEEE Photovoltaic Specialists Conference - 2000 (Cat. No.00CH37036), 2000
Multicrystalline Si (mc-Si) cells have not benefited from the cost-effective wet-chemical texturing processes that reduce front surface reflectance on single-crystal wafers. We developed a maskless plasma texturing technique for mc-Si cells using Reactive Ion Etching (RIE) that results in much higher cell performance than that of standard untextured cells. Elimination of plasma damage has been achieved while reducing front reflectance to extremely low levels. Internal quantum efficiencies higher than those on planar and wet-textured cells have been obtained, boosting cell currents and efficiencies by up to 11% on monocrystalline Si and 2.5% on multicrystalline Si cells.
Large-area multicrystalline silicon solar cell fabrication using reactive ion etching (RIE)
Solar Energy Materials and Solar Cells, 2011
Surface texturing of crystalline silicon wafer improves the conversion efficiency of solar cells by the enhancement in antireflection property and light trapping. Compared to antireflection coating, it is a more permanent and effective scheme. Wet texturing with the chemicals such as alkali (NaOH, KOH) or acid (HF, HNO 3 , CH 3 COOH) is too difficult for thinner wafer to apply due to a large amount of silicon loss. However, Plasma surface texturing using Reactive Ion Etching (RIE) can be effective in reducing the surface reflectance with low silicon loss. In this study, we have fabricated a large-area (156 Â 156 mm) multicrystalline silicon (mc-Si) solar cell by mask less surface texturing using a SF 6 /O 2 reactive ion etching. We have accomplished texturing with RIE by reducing silicon loss by almost half of that in wet texturing process. By optimizing the processing steps, we achieved conversion efficiency, open circuit voltage, short circuit current density, and fill factor as high as 16.1%, 619 mV, 33.5 mA/cm 2 , and 77.7%, respectively. This study establishes that it is possible to fabricate the thin multicrystalline silicon solar cells of low cost and high efficiency using surface texturing by RIE.
International Journal of Photoenergy, 2012
For lower reflectance, we applied a maskless plasma texturing technique using reactive ion etching (RIE) on acidic-textured multicrystalline silicon (mc-Si) wafer. RIE texturing had a deep and narrow textured surface and showed excellent low reflectance. Due to plasma-induced damage, unless the RIE-textured surfaces have the proper damage removal etching (DRE), they have a drop inVocand FF. RIE texturing with a proper DRE had sufficiently higher short circuit current(Isc)than acidic-textured samples without a drop in open circuit voltage(Voc). And in order to improve efficiency of mc-Si solar cell, we applied RIE texturing with optimized DRE condition to selective emitter structure. In comparison with the acidic-textured solar cells, RIE-textured solar cells have above 200 mA absolute gain in Isc. And optimized RIE samples with a DRE by HNO3/HF mixture showed 17.6% conversion efficiency, which were made using an industrial screen printing process with selective emitter structure.
RIE-Texturing of Industrial Multicrystalline Silicon Solar Cells
Journal of Solar Energy Engineering, 2005
Other researchers reported the development of an RIEtexturing process using Cl 2 gas, which textures many wafers per batch, making it attractive for mass-production [1]. Using this process, they have produced a 17.1% efficient 225-cm 2 mc-Si cell, which is the highest efficiency mc-Si cell of its size ever reported. This shows that RIE texturing can be done without causing performance-limiting damage to Si cells. In this paper, we will discuss an RIE-texturing process that avoids the use of toxic and corrosive Cl 2 gas.
Plasma-free Dry-chemical Texturing Process for High-efficiency Multicrystalline Silicon Solar Cells
Energy Procedia
In this paper, we study the influence of modifying the geometry of nanotexture on its electrical properties. Nanotexture is formed by an industrially feasible dry-chemical etching process performed entirely in atmospheric pressure conditions. A surface modification process is developed that allows low surface recombination velocities (S eff,min 10 cm/s) on nanotextured surfaces. By simultaneously improving the surface passivation and the emitter diffusion processes, we achieve an equivalent passivation level (V OC,impl 670 mV) for nanotextured surfaces to that of reference textured surfaces after applying either PECVD or ALD based deposition techniques.
Solar Energy Materials and Solar Cells, 2007
Alkali etchant cannot produce uniformly textured surface to generate satisfactory open circuit voltage as well as the efficiency of the multi-crystalline silicon (mc-Si) solar cell due to the unavoidable grain boundary delineation with higher steps formed between successive grains of different orientations during alkali etching of mc-Si. Acid textured surface formed by using chemicals with HNO 3-HF-CH 3 COOH combination generally helps to improve the open circuit voltage but always gives lower short circuit current due to high reflectivity. Texturing mc-Si surface without grain boundary delineation is the present key issue of mc-Si research. We report the isotropic texturing with HF-HNO 3-H 2 O solution as an easy and reliable process for mc-Si texturing. Isotropic etching with acidic solution includes the formation of meso-and macro-porous structures on mc-Si that helps to minimize the grain-boundary delineation and also lowers the reflectivity of etched surface. The study of surface morphology and reflectivity of different mc-Si etched surfaces has been discussed in this paper. Using our best chemical recipe, we are able to fabricate mc-Si solar cell of $14% conversion efficiency with PECVD AR coating of silicon nitride film. The isotropic texturing approach can be instrumental to achieve high efficiency in mass production using relatively low-cost silicon wafers as starting material with the proper optimization of the fabrication steps.
Semiconductor Science and Technology, 2005
Multi-crystalline silicon surface etching without grain-boundary delineation is a challenging task for the fabrication of high efficiency solar cells. The use of sodium hydroxide-sodium hypochlorite (NaOH-NaOCl) solution for texturing a multi-crystalline silicon wafer surface in a solar cell fabrication line is reported in this paper. The optimized etching solution of NaOH-NaOCl does not have any effect on multi-crystalline silicon grain boundaries and it also has excellent isotropic etch characteristics, which ultimately helps to achieve higher values of performance parameters, especially the open circuit voltage (V oc) and fill factor (FF), than those in the case of conventional silicon texturing. Easy control over the reaction of the NaOH-NaOCl solution is also one of the major advantages due to which sophistication in controlling the temperature of the etching bath is not required for the industrial batch process. The FTIR analysis of the silicon surface after etching with the current approach shows the formation of Si-Cl bonds, which improves the quality of the diffused junction due to chlorine gettering during diffusion. We are the first to report 14-14.5% efficiency of very large area (150 mm × 150 mm) multi-crystalline silicon solar cells using a NaOH-NaOCl texturing approach in an industrial production line with a yield greater than 95%.
Energy Procedia, 2013
In this work, we investigate the potential use of stain etched porous silicon as one possible way to increase the silicon solar cell efficiency at low cost. A very simple method for the formation of porous silicon antireflection coatings on random pyramid textured screen-printed monocrystalline silicon solar cells is described. The process is based on electroless metal-assisted chemical etching by immersion of the fully processed cell in HF-H 2 O 2-Ethanol without masking the contacts. Characterization of the porous silicon layer using SEM, EDX and UV-VIS-NIR spectrophotometry revealed that silver nanoparticles that are dissolved from the unmasked front grid contact by the HF acid greatly enhance the dissolution rate and therefore serve as catalysts for the porous silicon etching. The solar cell weighted reflectance was reduced from 45.08% to 22.01% after texturization and dropped further to 11.34% after porous silicon formation under optimized conditions. The porous silicon antireflection layer led to a relative improvement of 24.64% in the short-circuit current density without fill factor deterioration. The open-circuit voltage increased by ~7 mV and the cell efficiency was raised by 2.3% absolute. The simplicity of the process makes it attractive for the cost-effective production of silicon solar cells.
Solar Energy Materials and Solar Cells, 2010
Solar cells require surface texturing in order to reduce light reflectance, and to enhance light trapping. Anisotropic wet chemical etching is commonly used to form pyramids on the (1 0 0) silicon wafer surface by etching back to the (1 1 1) planes. In this paper, we used a low density silicon dioxide layer to allow etching in localized regions as an etch mask, forming inverted pyramid etch pits. Such an oxide can be deposited by plasma enhanced chemical vapor deposition using low deposition temperatures. The inverted pyramids are ideal for reducing surface reflectance, and are used in the highest efficiency silicon solar cells. Depending on the etch time and oxide quality, a variety of surface texture morphologies can be achieved. Due to the oxide mask, very little silicon is removed. This is an economical ideal method for texturing thin film single-crystalline silicon solar cells, as it combines the benefits of low reflectance with minimal thickness removed, while no photolithography is employed.
Efficiency improved by acid texturization for multi-crystalline silicon solar cells
Solar Energy, 2011
In this paper, we will show that efficiency of multi-crystalline silicon (mc-Si) solar cells may be improved by acid texturization. In order to enhance overall efficiency of mc-Si for solar-cell applications, the surface treatment of texturization with wet etching using appropriate solutions can improve incident light into the cell. Alkali etchant cannot produce uniformly textured surface to generate enough open circuit voltage (V OC) and high efficiency of the mc-Si due to the unavoidable grain randomly oriented with higher steps formed during etching process. Optimized acid etching conditions can be obtained by decreasing the reflectance (R) for mc-Si substrate below levels generated by alkali etching. Short-circuit current (I SC) measurements on acid textured cells reveal that current gain can be significantly enhanced by reducing reflection. The optimal acid etching ratio HF:HNO 3 :H 2 O = 15:1:2.5 with etching time of 60 s and lowering 42.7% of the R value can improve 112.4% of the conversion efficiency (g) of the developed solar cell. In order to obtain more detailed information of different defect region, high-resolution light beam induced current (LBIC) is applied to measure the internal quantum efficiency (IQE) and the lifetime of minority carriers. Thus, the acid texturing approach is instrumental to achieve high efficiency in mass production using relatively low-cost mc-Si as starting material with proper optimization of the fabrication steps.