Fabrication of optically smooth, through-wafer silicon molds for PDMS total internal reflection-based devices (original) (raw)
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Optical Evaluation of Silicon Wafers With Rounded Rear Pyramids
—We investigate the light trapping in Si wafers that are textured with conventional random pyramids on their front surface and rounded random pyramids on their rear. It is well established that rounding the pyramids leads to better surface passivation, but whether or not it improves light trapping depends on the cell structure. In this paper, we apply ray tracing, spectrophotome-try, and photoluminescence spectroscopy (PLS) to understand and quantify how rounding the rear pyramids might affect the light trapping in back-contact solar cells. We describe how rounding the pyramids leads to two competing optical effects: 1) reduced absorption in the rear films and 2) reduced scattering from the rear texture. The first effect improves light trapping whereas the latter degrades it. We show how the influence of each effect depends on wavelength and how they can be discerned (but not easily quantified) in reflectance curves. With PLS measurements, we conclude that for our sample structure and etch solution, the generation current is approximately constant for etch durations less than ∼60 s, and decreases significantly as the etch duration increases. Thus, by limiting the duration of the rounding etch, superior surface passivation can be attained without degrading the light trapping.
Surface Review and Letters, 2014
This paper investigates the combined e®ect of mechanical grooving and porous silicon (PS) on the front surface re°ectance and the electronic properties of crystalline silicon substrates. Mechanical surface texturization leads to reduce the cell re°ectance, enhance the light trapping and augment the carrier collection probability. PS was introduced as an e±cient antire°ective coating (ARC) onto the front surface of crystalline silicon solar cell. Micro-periodic V-shaped grooves were made by means of a micro-groove machining process prior to junction formation. Subsequently, wafers were subjected to an isotropic potassium hydroxide (KOH) etching so that the V-shape would be turned to a U-shape. We found that the successive treatment of silicon surfaces with stain-etching, grooving then alkaline etching enhances the absorption of the textured surface, and decreases the re°ectance from 35% to 7% in the 300-1200 nm wavelength range. We obtained a signi¯cant increase in the overall light path that generates the building up of the light trapping inside the substrate. We found an improvement in the illuminated I-V characteristics and an increase in the minority carrier lifetime eff . Such a simple method was adopted to e®ectively reinforce the overall device performance of crystalline silicon-based solar cells.
Optical analysis of textured plastic substrates to be used in thin silicon solar cells
Solar Energy Materials and Solar Cells, 2005
Light confinement strategies in thin-film silicon solar cells play a crucial role in the performance of the devices. In this work, the possible use of Ag-coated stamped polymers as reflectors to be used in n-i-p solar cells is studied. Different random roughnesses (nanometer and micrometer size) have been transferred on poly(methylmethacrylate) (PMMA) by hot embossing. Morphological and optical analyses of masters, stamped polymers and reflectors have been carried out evidencing a positive surface transference on the polymer and the viability of a further application in solar cells.
Microstructure and optical properties of layers formed by anodic etching of silicon
APPLIED PHYSICS OF CONDENSED MATTER (APCOM 2019), 2019
For various applications in optoelectronics and photovoltaics porous silicon structures are implemented for suppression of the spectral reflectance. We formed porous silicon structures by the anodic etching of p-type silicon substrates. Different etching conditions have been used in the forming procedure (electrical potential, current, and etching time) resulting in forming inhomogeneous structures with different microstructure and optical properties. The optical properties of formed structures are studied in our approach by application of the effective media approximation theory in construction of the spectral reflectance theoretical model. Thickness of formed layers, dielectric functions and volume fractions of structure components were extracted from optimized spectral reflectance model. Results of optical analysis correspond to the microstructure development during the sample forming.
Journal of Engineering Research, 2014
In this work, alkaline texturing of (100) crystalline Si and multicrystalline Si wafers in diluted KOH solution leading to pyramidal structures is studied as a function of the etching temperature. The surface morphology is investigated using Atomic Force Microscopy and Scanning Electron Microscopy and the surface reflectance is measured by spectrophotometry in the wavelength range 200-1200 nm. It is found that etching in diluted 1% KOH solution leads to incomplete surface texturing when the etching temperature is equal to 70 o C. The optimum etching temperature is found to be in the range 80-85 o C which results in a minimum surface reflectance for crystalline silicon covered with an antireflection coating of 0.8%, with a uniform distribution over a wider wavelength range for samples that received a saw damage removal in 30% KOH solution prior to texturing. On the other hand, the optimum etching temperature shifts to the higher range 85-95 o C for multicrystalline silicon surface with a minimum reflectance of 4.6% with ARC.
Heliyon, 2019
Continuing trend in silicon wafer thickness directed at cost reduction approaches basic boundaries created by: (a) mismatch between Al paste and Si wafer thermal expansion and (b) incomplete optical absorption. With its symmetrical front and back electrical contacts, the bifacial solar cell setup reduces stress due to mismatch thermal expansion, decreases metal use and increases high temperature efficiency. Efficiency improvement is accomplished in bifacial solar cells by capturing light from the back surface. Partially transparent wafers provide an option to improve near-infrared radiation absorption within Si wafer. To fully absorb optical radiation, threedimensional texture of these kinds of wafers is essential. Pulsed laser interactions, thermal oxidation, and wet chemical etching are included in this research. A feature of its energy and pattern setup is the interaction of pulsed laser with Si, running at 1.064 μm wavelength and micro-second length. Two experimental settings were explored: (a) post-laser chemical etching with potassium hydro-oxide etching with thermal oxide as etching mask and (b) post-laser heat Si surface oxidation. Due to fast melting and recrystallization, laser pulsed processing inherently produces its own texture. Some of these spherically-shaped, randomly focused characteristics improve inner scattering and boost near-infrared absorption within the wafer. These characteristics are separated during chemical etching with the thermally-grown oxide layer as an etch mask. Comparison of optical absorption in both surfaces shows almost a rise in the magnitude of absorption in non-etched surfaces. Detailed optical (optical microscope and IR absorption), morphological (field emission scanning electron microscope) and heat imaging (far IR camera) analyses were performed to comprehend physical processes that contribute to near-IR absorption improvement. Such kinds of partially-transparent, three-dimensional textured Si wafers are anticipated to discover applications for bifacial solar cells as substrates.
Journal of Microelectromechanical Systems, 2014
In this paper, we investigate the influence of different masking parameters onto the surface quality of the {111} sidewalls in order to generate specifically deep cavities by wet-anisotropic-etching of bulk silicon, for optical sensors using cavity sidewalls as reflectors. Mask alignment with crystal planes prior to wet-etching is found to be essential in order to avoid the appearance of additional planes during long etching. Mask deposition processes have been also evaluated. Among the different employed mask materials, Cr/Au gives the best results. It is then shown that cavities as deep as 1 mm with low roughness sidewalls can be simply produced with potassium hydroxide solution with periodic piranha cleaning.
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...