Chemical Texturing Used to Reduce The Reflectance of the Multi-Crystalline Silicon Wafer For Improving Optical Properties and Solar Cell Efficiency (original) (raw)
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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.
The texturization process during horizontal acidic etching of multi-crystalline silicon wafers
Materials Science in Semiconductor Processing, 2014
Horizontal wet-chemical etching of silicon wafers in an HF/HNO 3 /H 2 SiF 6 mixture is the most widely-used technique to texturize multi-crystalline silicon wafers for solar cell production. For the first time, the etch rates were determined separately for the upper and lower side during the horizontal texturization and the their different morphologies. The dependency of the surface morphology from the etch rate and etch depth is proven. Furthermore, the influence of the temperature and stirring rates on the morphological development for the upper and lower side of the wafer were examined. From temperaturedependent measurements, activation energies in the range from 17 kJ/mol to 40 kJ/mol on the upper side and from 23 kJ/mol to 40 kJ/mol on the lower side dependent from the etching time were determined. The observed results reveal a connection between the etch depth, the agitation of the etch solution, the morphology and the reflectivity of the separate wafer sides.
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.
Advanced Ceramics Progress, 2017
Surface texturing is one of the methods that improve the conversion efficiency of silicon-based solar cells by increasing the light trapping. The anisotropic texturing of p-type silicon (100) surface was performed using alkaline etching solution of sodium hydroxide (NaOH) including isopropyl alcohol (IPA) and hydrazine hydrate. The optical properties of etched wafers were investigated using reflectance spectrometer and morphology of surface was studied using scanning electron microscopy (SEM). Influence of NaOH concentration on etched wafers was studied and optimum value of surface reflectance was obtained by applying the best concentration of alkaline solution (NaOH).
This paper deals with the theoretical modeling of surface reflectance of acid textured multicrystalline wafer used in the processing of solar cell to minimize the surface reflectivity and there by enhancing the efficiency of the cell without wasting the wafers and time in optimizing the texturization process for the development of high efficiency solar cell. In the present study, texturization of mc-Si has been carried out in acidic solution using different compositions of HF, HNO3 and H3PO4 at different temperatures and for varying etching time (45-195 s). The best results were obtained for wet acidic ice cooled solution of HF:HNO3:H3PO4 :: 10:1:5 when textured for 165 s. Attempts have been made to explain the reflectivity behavior of the textured surfaces of the mc-Si wafers on the basis of the scanning electron microscopic (SEM) micrographs and theoretical modeling of reflectivity assuming the textured surface as a part of a hemisphere. It was observed that the average experimental reflectivity decreases as the etching time increases from 45 s to 165 s and attains a minimum value of 18% for the etching time of 165 s. The experimental reflectivity curve for the etching time of 165 s matches very well with the calculated reflectivity curve for h/D ratio of 0.50 in the wavelength range of 700-1050nm. These techniques are seems to be useful for large area industrial solar cell applications and the developed theoretical modeling software package may be suitably used for optimizing the texturization parameters of mc-Si wafers for achieving the minimal reflectance values for increasing the efficiency of solar cell.
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.
JOM, 2019
The present work addresses the exhaustive study of the surfaces of multicrystalline silicon wafers after being subjected to a texturization process for silicon heterojunction solar cell applications. The investigations described include the effect that the time of isotropic etching based on combinations of hydrofluoric and nitric acids has on the reflectance, the morphology of the surfaces and the surface recombination through the evolution of the implicit open-circuit voltage. The influence of previous treatments and the elimination of porous silicon or silicon oxide formed on wafer surfaces as a consequence of these texturization processes are also addressed. Textured multicrystalline silicon wafer surfaces with a good uniformity and low weighted hemispherical reflectances (23-24%) have been achieved with short etching times. These texturization processes have also been tested on upgraded metallurgical silicon wafers, resulting in weighted hemispherical reflectance values around 23%, but at the cost of the appearance of important surface defects.
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.
Materials Science and Engineering: B, 2009
The surface structure of multi-crystalline silicon (mc-Si) etched in HF/HNO 3 at different HF/HNO 3 concentrations is optimized for being applied in solar cells. The resulting texture, which determines the efficiency of solar cells, was characterized by means of scanning electron microscopy (SEM) and optical spectroscopy. The roughness of the surface increases and the reflectance decreases when the content of HNO 3 in the etching solution is increased to a limit. The produced etched pits on the surface have been identified by SEM and the surface mean roughness has been characterized by atomic force microscopy (AFM). Also, depending on the concentration of the electrolyte, the mc-Si samples exhibit photoluminescence in the VIS range under UV excitation. The PL reveals the presence of nanocrystals on the surface of the etched samples. The surface structure is also optimized for an adequate placement of the metallic contact on top. Finally the solar cells were performed in order to investigate the dependence of the roughness, reflectance and photoluminescence to the solar efficiency.