Metal-catalyzed Chemical Etching Research Articles

Broadband light absorption enhancement in nanoporous black silicon synthesized by aluminium-catalyzed chemical etching

Black silicon (b-Si) is an attractive light absorbing material for photovoltaic and optoelectronic applications due to its superior broadband light absorption. The b-Si is commonly synthesized using metal-catalyzed chemical etching (MCCE) process. In the recently developed aluminium-catalyzed chemical etching (ACCE) process, aluminium (Al) is being used as an effective catalyst to synthesize the nanoporous b-Si absorber. In this work, the broadband light absorption has been investigated in the nanoporous b-Si synthesized via ACCE process with varying etching duration (10–60 min). The etching of planar c-Si samples coated with 12 nm of Al film in a HF–H2O2–H2O (1-5-10 ml) solution for 30 min synthesizes the b-Si nanopores with average depth of 270.7 nm, average diameter of 41.6 nm, surface coverage of 54.7% and root mean square (RMS) roughness of 17.6 nm. With these morphological characteristics, the nanoporous b-Si demonstrates the lowest weighted average reflection (Ravg) of 9.2% and average absorption enhancement of 1.61 within 300–1100 nm spectral region. The findings from this work demonstrate the potential applications of the synthesized nanoporous b-Si absorber in photovoltaic and optoelectronic devices.

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.

Structural modification of diamond-wire-cut multicrystalline Si by Cu-catalyzed chemical etching for surface structuring

During the multicrystalline Si (mc-Si) solar cell production, metal-catalyzed chemical etching (MCCE) is an effective method for constructing texture surface on diamond wire sawing (DWS) cut mc-Si wafer. A dense Cu film was formed on silicon surface by Cu-MCCE, significantly restricting the etching process. In this work, FeCl3, MnO2 and H2O2, were selected to modify the structure of texture surface by one-step Cu-MCCE method. A wedge-shaped structure was formed when the concentration of FeCl3 and etching time are 0.2 mol/L and 15 min, and its reflectivity is 22.9%. A composite structure with shallow pits and nanopores was formed when the amount of MnO2 and etching time are 50 g/L and 20 min, and its reflectivity is 23.2%. An inverted pyramid structure was formed when the concentration of H2O2 and etching time are 3 mol/L and 15 min, and its reflectivity is 18.2%. The best conversion efficiency (η) of solar cell obtained is 19.0%, and, the depth-to-width ratio of texture structure is 1.33.

Energy management in hybrid organic-silicon nanostructured solar cells by downshifting using CdZnS/ZnS and CdZnSe/ZnS quantum dots

Management of the solar spectrum by downshifting has been a key theme in broadband solar cell research over the last few years. The absorption of high-energy photons that exceed the bandgap edge of Si causes thermalization of charge carriers, which is a major loss mechanism by which collected energy is underutilized in silicon solar cells. The spectral response of Si also falls in the UV region. Progress in overcoming these effects achieved by modifying the input spectrum will dramatically enhance power conversion efficiency (PCE). Herein we report the application of highly luminescent CdZnS/ZnS and CdZnSe/ZnS quantum dots (QDs) as downshifting materials for nanostructured silicon. The applied QDs show major potential for shifting the high energy in the ultraviolet region to low energy, which is then transferred to the underlying silicon nanostructures via radiative and nonradiative energy transfer. This energy transfer dramatically improves the cell efficiency from 10.4% to 13.5%, showing this approach to be a reliable solution for improving solar cell properties. A Novel hybrid organic/inorganic silicon nanotips solar cell employing CdZnS/ZnS QDs as a downshifting layer which exhibits a drastic enhancement in the cell characteristics due to the radiative and nonradiative energy transfer (RET & NRET) from the QDs to underlying silicon nanostructure. • Highly emissive CdZnS/ZnS and CdZnSe/ZnS core/shell QDs were prepared by hot injection in two growth steps. • Silicon nanowires were fabricated by metal-catalyzed chemical etching and modified to tapered nanotip structure. • The current QDs show high potential for downshifting in hybrid silicon solar cells and improve the PCE to 13.49%.

Metal-catalyzed chemical etching using DIO3 as a hole injection agent for efficient submicron-textured multicrystalline silicon solar cells

The introduction of ozonated deionized water (DIO3 water) to the silicon wafer wet cleaning process has attracted interest from the photovoltaic industry. In this work, a simple and cost-effective approach to fabricate submicron-texture multicrystalline silicon (mc-Si) wafer is presented using Ag metal-catalyzed chemical etching (MCCE) in DIO3/HF solution, where DIO3 was used as a hole injecting agent. The submicron-texture was successfully applied to fabricate efficient mc-Si PERC solar cells with an average efficiency of 20.31%, which is 0.58%abs higher than those with an acid micron-texture and exceeds those with conventional MCCE submicron-textures using H2O2 as the hole injecting agent. We demonstrated that using DIO3 as a hole injection agent in metal-catalyzed chemical etching is feasible. This novel MCCE approach is simple, low-cost, and ecofriendly, making it an attractive alternative to conventional MCCE methods for use in industrial-scale production.

The Role of Metal-Catalyzed Chemical Etching Black Silicon in the Reduction of Light- and Elevated Temperature-Induced Degradation in P-Type Multicrystalline Wafers

Light- and elevated temperature-induced degradation (LeTID) of silicon wafers reduces the energy yield of photovoltaic modules in the field. A previous study demonstrated that this degradation is greatly reduced in samples with a surface textured with black silicon formed via reactive ion etching. However, the reason for this reduction is currently not understood. This article extends that result to a range of nano-textures formed using commercial metal-catalyzed chemical etching. Lifetime test structures are fabricated on multicrystalline wafers with six different chemical nano-textures and the results are compared to planar reference samples. The article demonstrates a reduction in the extent of light-induced degradation compared to planar reference samples for all six textures. The extent of LeTID is observed to reduce with decreasing front surface reflectance and increasing front surface area. The article finds that wafer thickness, phosphorus gettering, and fast-firing cannot explain the result.

Effects of surface morphology on Ag crystallite formation in screen-printed multi-crystalline Si solar cells

The electrode collects electrons produced by a solar cell. Ag crystallites generated during front electrode formation play an important role in transferring electrons from the emitter to the Ag finger. Previously, the formation mechanism of Ag crystallites and the various factors influencing Ag crystallite formation have been studied, including the effect of surface morphology on Ag crystallite formation. The glass coverage varies with the texture of the Si surface, and thus the degree of exposure of the Si surface varies correspondingly. When the Si surface is exposed, direct contact is achieved, and contact resistance is improved. However, the effect of surface morphology on the Ag crystallites formed on the Si surface under the glass layer has not yet been studied. The effect of surface morphology on Ag crystallite formation is presented in this work. Two multi-crystalline Si wafers with different surface morphologies were compared. The first multi-crystalline Si wafer was textured using metal-catalyzed chem ical etching (MCCE). The second multi-crystalline Si wafer was textured by MCCE followed by reactive ion etching. Wafers with sharper textures had lower series resistances, higher fill factors, and a large amount of Ag crystallites. Ag crystallites primarily formed at the tips of the texture. To analyze the effect of surface morphology, the surface electron concentration was confirmed by simulation. Electron concentration at the tip was proportional to the sharpness of the tip. Therefore, when the firing process is performed at the same temperature, wafers with sharper tips are expected to exhibit better electrode characteristics.

On the Enhanced Phosphorus Doping of Nanotextured Black Silicon

The integration of nanotextured black silicon (B-Si) into solar cells is often complicated by its enhanced phosphorus doping effect, which is typically attributed to increased surface area. In this article, we show that B-Si's surface-to-volume ratio, or specific surface area (SSA), which is directly related to surface reactivity, is a better indicator of reduced sheet resistance. We investigate six B-Si conditions with varying dimensions based on two morphology types prepared using metal-catalyzed chemical etching and reactive-ion etching. We demonstrate that for a POCl3 diffusion, B-Si sheet resistance decreases with increasing SSA, regardless of surface area. 2-D dopant contrast imaging of different textures with similar surface areas also indicates that the extent of doping is enhanced with increasing SSA. 3-D diffusion simulations of nanocones show that both the extent of radial doping within a texture feature and the metallurgical junction depth in the underlying substrate increase with increasing SSA. We suggest SSA should be considered more readily when studying B-Si and its integration into solar cells.

Texturing Technology on Multicrystalline Silicon Wafer by Metal-catalyzed Chemical Etching: a Review

Texturing Technology on Multicrystalline Silicon Wafer by Metal-catalyzed Chemical Etching: a Review

Surface damage and metal-catalyzed chemical etching investigation of multicrystalline silicon by diamond wire sawing

Cutting silicon ingots into silicon wafer is a crucial step in solar cell production process. As a major cutting technique, diamond wire sawing (DWS) has already completely replaced the multi-wire slurry sawing (MWSS). In this work, the essential features of diamond wire cut multicrystalline silicon wafer, behavior of surface damage, formation mechanism, removal of damage layer, and influence of damage layer on making texture surface and performance of solar cells were investigated. Amorphous layer and defects layer are found on the surface of DWS wafer, which restricts the process of making texture. By using metal-catalyzed chemical etching (MCCE) method to make texture surface, the etching rate is faster without damage layer than with damage layer, and the reflectivity can be reduced from 19.08% to 14.79%. After removing the damage layer, the conversion efficiency of solar cell is 17.29%, which is 2.35% higher than that of the cell with the damage layer.

Effect of Microstructures With Different Depth-to-Width Ratios on Surface Reflectance and Si Solar Cell Performance

Metal-catalyzed chemical etching (MCCE) is an effective method for making texture surface on diamond wire saw (DWS) cut mc-Si wafer. In this work, microstructures with different depth-to-width ratios were obtained by MCCE on the surface of DWS cut mc-Si wafers. Simultaneously, the influence of etching time and the concentration of AgNO3 on etching depth, surface reflectance performance, and effect of reaming on the solar cell performance were studied. In total, 12 microstructures with different depth-to-width ratios ranging from 0.63 to 5.31 were prepared. The etching rate increased with the increase in concentration of AgNO3 and etching time. Moreover, the depth-to-width ratio significantly affected the reflectivity of silicon wafers. The relationship between them can be expressed by the fitting exponential function: y = 12.41 × x −0.733. The reflectivity obtained in the experiment ranged from 3.71% to 18.15%. After reaming, the performance of the mc-Si solar cells has been significantly improved, and η could reach up to 18.53%.

Improvement of the Surface Structure for the Surface Passivation of Black Silicon

Black silicon (B-Si) has been extensively applied in the photovoltaic field for its prominent light-trapping feature, but its large surface area also brings plenty of structural defects. In this article, a postetching treatment by using acid mixed solution consisted of HNO3/HF/H2O was adopted to balance the tradeoff between optical gain and electrical losses on metal-catalyzed chemical etching B-Si surfaces. We studied the effect of etching time on the reflectance and surface passivation of B-Si on polished and pyramid textured silicon substrates. The result shows that compared with the NaOH postetching applied in the industrial product line, the acid mixed solution could improve the surface passivation and low reflectance within the etching time of 3 min. Moreover, on the base of industrial anisotropic NaOH etch procedure, within etching time of 2 min, the reflectance and Seff decreased by 2.93% and 36.5 cm/s respectively. This fast and combined postetching treatment is a potential industrial method to obtain low reflectance and surface recombination loss.

Effective Additive-Free Acidic-Solution Texturing for Surface-Damage-Free Kerfless Silicon Wafers

Crystalline solar cells have attracted significant attention in the solar-cell market owing to their low material cost. Multicrystalline silicon (mc-Si) is usually fabricated using the casting method, and approximately 35% of Si is removed as kerf in the sawing process performed to fabricate the wafer. The fabrication of kerfless mc-Si wafers does not involve the sawing and growing process. Hence, there is a significant reduction in the process cost (∼50%), while saving ∼66% energy in wafer manufacturing. Moreover, the absence of sawing process will result in no surface damage and smoother surfaces. Texturing using conventional methods such as acidic chemical etching are ineffective and as a result, the desired surface texture cannot be obtained. To solve this problem, the texture can be created using relatively expensive and complicated processes such as reactive-ion etching or metal-catalyzed chemical etching, which are not affected by the shape of the wafer surface. This article proposes a method for creating an effective texture that can increase the light absorptivity of mc-Si wafers manufactured by the kerfless method with no surface damage. This technology is a cost-effective and reliable process that uses an acidic chemical solution with no additive or mask. The etching rate and texture shape are investigated for different solution ratios of HF and HNO3. The surface morphology is examined using scanning electron microscopy, and the reflectance at 300–1200 nm is measured using ultraviolet–visible spectroscopy. A weighted average reflectance of ∼20.0% is obtained, which reduces to ∼7.4% on depositing an antireflective film.

Complementary etching behavior of alkali, metal‐catalyzed chemical, and post‐etching of multicrystalline silicon wafers

AbstractBoth alkali and metal‐catalyzed chemical etching (MCCE) of multicrystalline silicon (mc‐Si) wafer show anisotropic etching behavior, resulting in different morphologies among the different grains. However, by combining alkali etching, MCCE, and a post‐etching process, homogeneous microstructures can be obtained on the surface of mc‐Si wafer. After the first alkali etching, there are three typical morphologies of upward pyramids, terraces, and tilt planes, and relative to the initial Si(100), Si(110), and Si(111) dominated grains, these show low, moderate, and high reflection, respectively. After MCCE and the post‐etching process, the microstructures on the different grains have converged to a similar morphology and reflection. Mc‐Si solar cells fabricated by complementary alkali etching, MCCE, and post‐etching have a good appearance and high efficiency of ~19.4%. Moreover, the cells with submicrometer texture have the advantages of reverse current‐voltage characteristics and weak light response over traditional cells with micrometer texture.

18.88%-efficient multi-crystalline silicon solar cells by combining Cu-catalyzed chemical etching and post-treatment process

Mass production of diamond-wire-sawn (DWS) multi-crystalline silicon (mc-Si) solar cells reached a significant point of maturity through utilization of metal-catalyzed chemical etching (MCCE). However, the reported studies always focus on how to optimize the MCCE process but there are few studies concentrating on the post-treatment techniques to improve the cell efficiency. In this paper, we use a combination of Cu-MCCE method and a HF/HNO3/H3PO4 post-processing treatment process to decorate the surface of Si textures for the first time. The submicron polygonal chamfered cone structure produced by the post-processing treatment is demonstrated to be helpful in reducing surface recombination and improving the cell performance in terms of surface morphology, reflectivity, internal quantum efficiency (IQE) and external quantum efficiency (EQE) measurements as well as Electroluminescence (EL) spectra characterizations. The highest efficiency of Cu-MCCE mc-Si solar cells subjected to such post-processing treatment process is 18.88% with short circuit current (Isc), open circuit voltage (Voc) and fill factor (FF) of 36.67 mA/cm2, 638.6 mV and 80.64%, respectively, in great contrast to that (16.81%) of Cu-MCCE mc-Si solar cells without any post treatment. The post-treatment process is, therefore, of great potential for the Si photovoltaic industry, especially for the Cu-MCCE mc-Si solar cells.

Comparison of different etching methods on the morphology and semiconductor characters of black silicon

Femtosecond laser etching, deep reactive ion etching and metal-catalyzed chemical etching are used to fabricate black silicon. It has been found that the light absorption is significantly enhanced in the wavelength of 400∼2200nm, in which the absorption in near infrared band of black silicon etched by femtosecond laser with SF6 has the highest value. It is observed that, however, the minority carrier lifetime of crystalline silicon is shortened to some extent, which can be adjusted and controlled effectively by depositing SiNx film to passivate the surface of black silicon. Finally, a PIN photodetector is manufactured based on black silicon and a higher responsibility of 0.57 A/W at 1060 nm is obtained compared to the PIN silicon photodetector without etching process.

A simple and low-cost chemical etching method for controllable fabrication of large-scale kinked silicon nanowires

In this paper, large-area and uniform kinked silicon nanowires (SiNWs) in Si(111) have been fabricated by an alternating metal-catalyzed chemical etching (AMCCE) method. The etching direction alternating between [111] and [100] is highly controllable in this system, and the morphology of kinked SiNWs can be customized easily through controlling the alternating frequency. Good anti-reflection properties were proved by UV–vis spectrophotometer, the average reflectance at 200–1100nm is less than 10%, and moreover, the reflectance can be as low as 6% in the visible region (380–780nm), which shows a promising potential application as an anti-reflection structure in the photovoltaic field.

Constructing submicron textures on mc-Si solar cells via copper-catalyzed chemical etching

Mass production of diamond-wire-sawn (DWS) multicrystalline silicon (mc-Si) solar cells reached a significant point of maturity through utilization of metal-catalyzed chemical etching (MCCE). However, nanotextured DWS mc-Si solar cells usually produced with Ag-MCCE still suffer from certain drawbacks, such as remaining saw marks, color differences among grains, and slight decreases in the open-circuit voltage (Voc). In this work, we show that unoriented Cu-based MCCE (Cu-MCCE) not only depresses the saw marks and color differences but also introduces random shallow pits, which act as artificial defects that can be easily converted into a submicron texture using conventional HNO3/HF etching. Moreover, we demonstrate that the efficiency of DWS mc-Si solar cells produced with the Cu-MCCE process is greater than 19%, with improved Voc resulting from better surface passivation. This cost-effective Cu-MCCE method is, therefore, of significant potential for the photovoltaic industry.

Efficient nanostructured quasi-single crystalline silicon solar cells by metal-catalyzed chemical etching

Seed-assisted cast quasi-single crystalline silicon (Qsc-Si) technique allows the production of efficient, low-cost solar cells. However, most of the Qsc-Si wafers still consist of single- and multi-crystalline silicon grains, which lead to difficulties when attempting to achieve high efficiency by using conventional acid or alkali texture processes. This paper highlights the fact that nano-textured Qsc-Si solar cells can reach efficiencies ranging from 18.4% to 18.9% by using the same metal-catalyzed chemical etching technique, along with a depressed color difference. A parallel sub-cell model is proposed to explain how to enhance the performance of Qsc-Si cells.

High-Performance Black Multicrystalline Silicon Solar Cells by a Highly Simplified Metal-Catalyzed Chemical Etching Method

A wet-chemical surface texturing technique, including a two-step metal-catalyzed chemical etching (MCCE) and an extra alkaline treatment, has been proven as an efficient way to fabricate high-efficiency black multicrystalline (mc) silicon solar cells, whereas it is limited by the production capacity and the cost cutting due to the complicated process. Here, we demonstrated that with careful control of the composition in etching solution, low-aspect-ratio bowl-like nanostructures with atomically smooth surfaces could be directly achieved by improved one-step MCCE and with no posttreatment, like alkali solution. The doublet surface texture of implementing this nanobowl structure upon the industrialized acidic-textured surface showed concurrent improvement in optical and electrical properties for realizing 18.23% efficiency mc-Si solar cells (156 mm × 156 mm), which is sufficiently higher than 17.7% of the solely acidic-textured cells in the same batch. The one-step MCCE method demonstrated in this study may provide a cost-effective way to manufacture high-performance mc-Si solar cells for the present photovoltaic industry.