Formation of inverted pyramid-like structures on surfaces of single crystalline silicon solar cells by chemical wet etching (original) (raw)
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Journal of vacuum science and technology, 2013
The creation of nanostructures on polycrystalline silicon wafer surface to reduce the solar reflection can enhance the solar absorption and thus increase the solar-electricity conversion efficiency of solar cells. The self-masking reactive ion etching (RIE) was studied to directly fabricate nanostructures on silicon surface without using a masking process for antireflection purpose. Reactive gases comprising chlorine (Cl 2), sulfur hexafluoride (SF 6), and oxygen (O 2) were activated by radio-frequency plasma in an RIE system at a typical pressure of 120-130 mTorr to fabricate the nanoscale pyramids. Poly-Si wafers were etched directly without masking for 6-10 min to create surface nanostructures by varying the compositions of SF 6 , Cl 2 , and O 2 gas mixtures in the etching process. The wafers were then treated with acid (KOH:H 2 O ¼ 1:1) for 1 min to remove the damage layer (100 nm) induced by dry etching. The damage layer significantly reduced the solar cell efficiencies by affecting the electrical properties of the surface layer. The light reflectivity from the surface after acid treatment could be significantly reduced to <10% for the wavelengths between 500 and 900 nm. The effects of RIE and surface treatment conditions on the surface nanostructures and the optical performance as well as the efficiencies of solar cells will be presented and discussed. The authors have successfully fabricated large-area (156 Â 156 mm 2) subwavelength antireflection structure on poly-Si substrates, which could improve the solar cell efficiency reproducibly up to 16.27%, higher than 15.56% using wet etching. V
Cornell University - arXiv, 2022
Silicon inverted pyramids arrays have been suggested as one of the most promising structure for high-efficient ultrathin solar cells due to their ability of superior light absorption and low enhancement of surface area. However, the existing techniques for such fabrication are either expensive or not able to create appropriate structure. Here, we present a lithography free method for the fabrication of inverted pyramid arrays by using a modified metal assisted chemical etching (MACE) method. The size and inter-inverted pyramids spacing can also be controlled through this method. We used an isotropic chemical etching technique for this process to control the angle of etching, which leads to ultra-low reflection, even < 0.5%, of this nanostructure. Using this specification, we have predicted the expected solar cell parameters, which exceeds the Lambertian limit. This report provides a new pathway to improve the efficiency of the ultrathin silicon solar cells at lower cost.
Rounded Rear Pyramidal Texture for High Efficiency Silicon Solar Cells
— Interdigitated back-contact (IBC) solar cells developed in the past two years have efficiencies in the range 24.4%–25.6%. As high as these efficiencies are, there are opportunities to increase them further by improving on the light trapping. Silicon solar cells incorporating double-sided pyramidal texture are capable of superior light trapping than cells with texture on just the front. One of the principle losses of double-sided pyramidal texture is the light that escapes after a second pass through the cell when the facet angles are the same on the front and rear. This contribution investigates how this loss might be reduced by changing the facet angle of the rear pyramids. A textured pyramid rounding is introduced to improve the light trapping. The reduction in surface recombination that rounding the facets introduces is also evaluated. With confocal microscopy, spectrophotometry and ray tracing, the rounding etch time required to yield the best light trapping is investigated. With photoconductance lifetime measurements, the surface recombination is found to continue to decrease as the rounding time increases. The spectrophotometry and ray tracing suggests that the double sided textured samples featuring rounded rear pyramids have superior light trapping to the sample with a planar rear surface. The high-efficiency potential of rounded textured pyramids in silicon solar cells is demonstrated by the fabrication of 24% efficient back-contact silicon solar cells.
Solar Energy Materials and Solar Cells, 2011
In this paper, we present a multi-crystalline solar cell with hexagonally aligned hemispherical concaves, which is known as honeycomb textured structure, for an anti-reflecting structure. The emitter and the rear surface were passivated by silicon nitride, which is known as passivated emitter and rear (PERC) structure. The texture was fabricated by laser-patterning of silicon nitride film on a wafer and wet chemical etching of the wafer beneath the silicon nitride film through the patterned holes. This process succeeded in substituting the lithographic process usually used for fabricating honeycomb textured structure in small area. After the texturing process, solar cells were fabricated by utilizing conventional fabrication techniques, i.e. phosphorus diffusion in tube furnace, deposition of anti-reflection film and rear passivation film by chemical vapor deposition, front and rear electrodes formation by screen printing, and contact formation by furnace. By adding relatively small complicating process to conventional production process, conversion efficiency of 19.1% was achieved with mc-Si solar cells of over 200 cm 2 in size.
Progress in Photovoltaics: Research and Applications, 1997
In this paper, we report inverted pyramidal nanostructure based multi-crystalline silicon (mc-Si) solar cells with a high conversion efficiency of 18.62% in large size of 156 Â 156 mm 2 wafers. The nanostructures were fabricated by metal assisted chemical etching process followed by a post nano structure rebuilding (NSR) solution treatment. With increasing NSR treatment time, the reflectance and the dimensions of micro oval pits were both influenced. Resulting from both the light trapping ability and passivation efficiency, 500 nm inverted pyramid structure exhibited an ideal solar cell performance. The best solar cell showed a low reflectivity of 3.29% and a 0.91 mA cm À2 increase of short-circuit current density, and its efficiency was 0.45% higher than the acid textured solar cell. This technique presented a great potential to be a standard process for producing highly efficient mc-Si solar cells in the future.
Technological process for a new silicon solar cell structure with honeycomb textured front surface
Solar Energy Materials and Solar Cells, 2006
This paper presents a new silicon solar-cell structure improved by texturisation of the front surface using silicon micromachining technologies. A 'honeycomb'-textured front surface has been obtained through a photolithographical process to generate patterns (disc holes) on the front surface followed by isotropic etching (in HNO 3 : HF: CH 3 COOH) until the wells joined together.
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.
Journal of Power and Energy Engineering, 2020
Texturing of diamond wire cut wafers using a standard wafer etch process chemistry has always been a challenge in solar cell manufacturing industry. This is due to the change in surface morphology of diamond wire cut wafers and the abundant presence of amorphous silicon content, which are introduced from wafer manufacturing industry during sawing of multi-crystalline wafers using ultra-thin diamond wires. The industry standard texturing process for multi-crystalline wafers cannot deliver a homogeneous etched silicon surface, thereby requiring an additive compound, which acts like a surfactant in the acidic etch bath to enhance the texturing quality on diamond wire cut wafers. Black silicon wafers on the other hand require completely a different process chemistry and are normally textured using a metal catalyst assisted etching technique or by plasma reactive ion etching technique. In this paper, various challenges associated with cell processing steps using diamond wire cut and black silicon wafers along with cell electrical results using each of these wafer types are discussed.
Investigation of Novel Silicon PV Cells of a Lateral Type
Silicon, 2014
Solar cells made of single-crystalline silicon, as alternative energy sources, became the most widely used solar cells in recent years. The mainstream manufacturing approach is to process the cells and assemble these into photovoltaic (PV) modules. However, the direct conversion of solar energy into electricity using the PV effect suffers from low efficiency. Thus, increasing the conversion efficiency at low production costs becomes the main goal of solar cell manufacturers. One way to increase the efficiency of a solar cell is to use an ultra-wide layer of intrinsic semiconductor as the depletion region of a PN junction. In our work, we present a novel geometrical concept of PIN structure for PV applications. The width of the intrinsic layer in our construction is 5-20 mm. Moreover, in our novel structure, the light irradiation acts directly on the active region of the PV cell, which enables bi-facial irradiation and results in ∼28 % conversion efficiency. A low cost fabrication is ensured in our design due to a new manufacturing technology by eliminating some expensive processes, such as photolithography. The feasibility proof of the novel concept in mono-crystalline silicon solar cells is presented. We demonstrate simulation results and preliminary experimental results confirming our approach.
Materials Science in Semiconductor Processing, 2015
Textured surface is commonly used to enhance the efficiency of silicon solar cells by reducing the overall reflectance and improving the light scattering. In this study, a comparison between isotropic and anisotropic etching methods was investigated. The deep funnel shaped structures with high aspect ratio are proposed for better light trapping with low reflectance in crystalline silicon solar cells. The anisotropic metal assisted chemical etching (MACE) was used to form the funnel shaped structures with various aspect ratios. The funnel shaped structures showed an average reflectance of 14.75% while it was 15.77% for the pillar shaped structures. The average reflectance was further reduced to 9.49% using deep funnel shaped structures with an aspect ratio of 1:1.18. The deep funnel shaped structures with high aspect ratios can be employed for high performance of crystalline silicon solar cells.