Optimization of Chemical Texturing of Silicon Wafers Using Different Concentrations of Sodium Hydroxide in Etching Solution (original) (raw)
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Improved anisotropic etching process for industrial texturing of silicon solar cells
Solar Energy Materials and Solar Cells, 1999
An experimental study on the surface texturisation of monocrystalline wafers with solutions containing sodium-hydroxide and isopropanol was carried out. Both the composition and the temperature of the etching solution were optimised on the basis of etch-rate measurements on silicon samples having different crystallographic directions. It was found that the density and the size of the pyramids are influenced by the etch-rate of silicon in the 11 0 02 direction and also by the anisotropy factor of the solutions being the quotient of the etch rate in the 11 0 02 to 11 1 12 directions. Design of experiments and response surface methods were used to extract the etch rate as a function of different input parameters, such as the sodium hydroxide and isopropanol concentrations and the temperatures of the solutions. Optimum texturing conditions were found at a temperature of 80°C and a composition which causes a relatively high etch rate in the 11 0 02 direction with an anisotropy factor of 10. At the starting point of the etching process, the inhomogeneity of pyramid nucleation can be avoided by mixing an additive to the texturing solution. With such a solution, the pyramid size can be tuned by varying the etching time in order to obtain a low reflectivity from the textured silicon wafers. Based on our results the texturing process could be stabilised with respect to the reproducibility on a large scale of wafers.
2021
The aim of this work is to improve the optical properties in the multi-crystalline silicon (mc-Si) by acid texturization. Generally, HF and HNO3 are using the mc-Si wafer acid texturization process and it is toxic chemical acids. In this work, H2O2 is used instead of HNO3 because of H2O2 less toxic chemical compared to HNO3. In this work, we have used the different types of chemical acids in different ratios for etching. Here, we have used HF: H2O2: CH3COOH=3:2:2, HF: H2O2: KMnO4 =3:2:0.2 M and HF: H2O2: HNO3: KMnO4 =3:2:2:0.2M for etching with the etching time of 60 sec. The HF: H2O2: KMnO4 =3:2:0.2M gives the better results as obtained from optical microscope, UV- Visible reflectance studies and X-ray diffraction (XRD) studies. The etched mc-Silicon wafer surface was analyzed by the optical microscope and Scanning Electron Microscope (SEM). The FTIR results indicate the reduction of oxidation in the etched samples. Moreover, the HF: H2O2: KMnO4 =3:2:0.2M textured wafers have the a...
Pyramidal texturing of silicon solar cell with TMAH chemical anisotropic etching
Solar Energy Materials and Solar Cells, 2006
High-efficiency silicon solar cells need a textured front surface to reduce reflectance and to improve light trapping. Texturing of monocrystalline silicon is usually done in alkaline solutions. These solutions are cheaper, but are pollutants of silicon technologies. In this paper, we investigate an alternative solution containing tetramethyl ammonium hydroxide ((CH 3) 4 NOH, TMAH). This study shows the influence of different parameters (concentration, agitation, duration and temperature), to obtain uniform and reliable pyramidal texturization on different silicon surfaces (as cut, etched and polished). Under optimized conditions, TMAH-textured surface led to an average weighted reflectance of 13%, without any antireflection coating independent of the initial silicon surface. Unlike potassium hydroxide (KOH) texturing solution, characterization of silicon oxide layer contamination after TMAH texturing process revealed no pollution, and passivation is less affected by TMAH than by KOH texturization.
Highly-efficient low cost anisotropic wet etching of silicon wafers for solar cells application
AIP Advances, 2018
In this work, a novel aqueous etching solution was investigated for texturization of silicon substrates. Nearly 30% of incident light is reflected from the surface of crystalline silicon due to its high refractive index. Surface texturization is an efficient practice to reduce surface reflection by enhancing light trapping. Newly formulated etching solution was evaluated for optical reflection, surface morphology and hydrophilicity of silicon substrates. Amazingly, experimental results demonstrate lowest optical reflectance, improved surface morphology as well as enhanced periodicity of the resulting pyramids. A remarkably lowest surface reflectance of 9.94% was achieved. Meanwhile, addition of IPA in the solution plays a major part in improving hydrophilicity of the silicon substrates.
In this paper, the anisotropic nature of tetramethyl ammonium hydroxide (TMAH) etchant solution (without additives) has been exploited to study the effects of various surface texturing conditions towards morphology and surface reflectivity of p-type (100) monocrystalline silicon (Si) substrates for solar cells applications. 2x2 cm 2 samples were textured at 90°C in low concentrations TMAH with different weight percentages (3 wt.%, 5 wt.% and 8 wt.%) for 10, 20 and 30 minutes respectively. The morphology of the textured samples was inspected by scanning electron microscope (SEM) and atomic force microscopy (AFM). Resulting surface reflectivity was measured on optical reflectometer. It was observed that TMAH of 5 wt.% with 10 minutes surface texturing process produced the highest density of random pyramids, highest root mean square (RMS) of surface roughness with the lowest surface reflectivity of about 7% (weighted average) within 400-1000 nm region. Higher TMAH wt.% or longer processing time resulted in a smoother wafer surface hence with higher reflectance. The results of SEM, AFM and surface reflectivity were compared to the result of a reference p-type (100) monocrystalline Si substrate (untextured) respectively. The effects of different TMAH surface texturing conditions towards the morphology and surface reflectivity of monocrystalline Si substrates for solar cells applications were subsequently discussed.
Optik, 2018
In this study, monocrystalline p-type Czochralski silicon wafers having dimension 127×127 mm 2 , thickness 200 µm, and plane (100) were textured to optimize the surface reflection for the fabrication of efficient solar cell. Properly cleaned silicon wafers were textured with the systematic variation of the etching time and chemical concentration (KOH and IPA) at 70 °C temperature. According to field emission scanning electron microscope (FESEM) images and surface reflection measurement (SRM) data, the wafer textured with 10 minutes etching time and the wafer textured with 1 gm of KOH concentration, both showed the similar minimum optical reflectance of 15.08 %. This lower reflectance was due to the formation of uniform pyramidal structure on the wafer surface. Moreover, the wafer surface textured with 7 ml isopropyl alcohol (IPA) showed the lowest surface reflectance of 13.59 % because of the formation of more uniform pyramidal structure. The most effective pyramidal structure for fabricating efficient solar cell was found for 10 minutes etching with optimum chemical recipe of KOH: IPA: H2O = 1 gm: 7 ml: 125 ml.
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.
Optical and Electrical Properties of Silicon Solar Cells by Wet Chemical Etching
Journal of the Chilean Chemical Society, 2019
We present a simple method for the texturing of commercial silicon solar cells in a two-step process by etching in an HF solution containing H 2 O 2. This etching process is facilitated by silver nanoparticles which act as catalytic sites. The etching times for the fabrication of nano-pores on the surface are established. The optical properties of the nano-structures on the surface of silicon solar cell were investigated by spectrometer measurements. The samples presented a total reflection coefficient lower than that of silicon solar cells without the treatment. The global efficiency of the silicon solar cell depends on the chosen preparation conditions for the silver ion concentration, and time of wet etching. The textured surface of solar cells showed an increase in efficiency, with a circuit photocurrent higher than that of a reference silicon solar cell without texturing. The J-V curves of various silicon cells are presented and discussed in correlation with the surface morphology.
Anisotropic etching of p-type Single crystalline (100) silicon substrate was optimized using KOH and IPA etchant combinations at constant temperature. Surface texturing histogram of the etched silicon substrates at different combinations were characterized using Zeta analysis, Scanning Electron Microscope and UV–vis spectral reflectance measurements. An increase in etchant ratio results in an increase in aspect ratio (height/base) and a decrease in the density of pyramid. Optimization of etchant ratio to 3:1 resulted in the presence of correlated pyramid distribution with an average aspect ratio of 0.44 and resulted in a lowest weighted reflectance of 10.76% for the spectral range from 300 nm to 1100 nm without anti-reflection coating.
IEEE Journal of Photovoltaics, 2019
Cost-effective solar cell can be fabricated with the use of multicrystalline silicon (mc-Si) wafer. Accordingly, texturization of an mc-Si surface is an important step for fabrication of an mc-Si solar cell as it reduces reflection of light from the surface of the cell. In this study, wet isotropic etchant composition of HF-HNO 3-H 2 SO 4-H 2 O has been considered to texture the mc-Si wafer as a cost-effective and reliable process at room temperature with a faster convergence rate. Concentration variation of H 2 SO 4 in the wet acid etchant on both mc-Si etching thickness and etching rates has been studied. Subsequently, the surface morphology has been investigated with the use of field emission scanning electron microscope (FESEM) photograph, which exhibits the nanoporous structures on the surface of the mc-Si wafer. Further, the reflectance from the etched surface of mc-Si also has been measured for the wavelength ranges from 200 to 1200 nm and has been found to be from 3% to 6% to etch with the said acid composition.