Textured Silicon Surface Research Articles

Photovoltaic enhancement of Si micro- and nanostructure solar cells via ultrafast laser texturing

The purpose of the present study was to achieve laser-microtextured Si structures, the material used as silicon wafers, with a thickness of 330 mu m for a fast laser texturing technique, in order to produce micro-/nanosurface textures by means of a UV femtosecond laser. A textured silicon surface was prepared that has the capability to trap light, thereby greatly reducing the visible light reflection for photovoltaic cells. The textured surface was measured by scanning electron microscope. The results showed a photocurrent increase of about 25% in the laser-textured zones.

Investigation of Laser Ablation Induced Defects in Crystalline Silicon Solar Cells

In this paper, the laser induced defects that result from a picosecond laser ablation (wavelength 355mm) of passivating SiO2 and SiNx layers on textured silicon surface are investigated for various laser fluence ranging from 0.48J/cm2 to 1.43J/cm2. In the first part of this paper, we employ the Wright etching technique to identify and quantify thermally propagated dislocations as one of the resulting defects as a function of the laser fluence. Dislocations densities in the order of 4 - 13 x 106 cm-2 are measured. The second part of the paper takes a closer look at the impact of laser induced defects on the effective lifetime and surface recombination current. By comparing both parameters on structures with laser ablation and photo-lithography to pattern the dielectric, it is observed that dislocations formed during the laser ablation process do indeed enhance minority carrier recombination within the silicon wafers. The recombination current at the laser ablated area, for a moderate laser power, is shown to be four times larger than in the case of using lithography.

Numerical Simulation of Non-Ablative Laser Texturing of Silicon Surface with a Continuous Wave Fiber Laser

Numerical Simulation of Non-Ablative Laser Texturing of Silicon Surface with a Continuous Wave Fiber Laser

Low-reflective surface texturing for large area multicrystalline silicon using NaOH-NaClO solution

Multicrystalline silicon surface texturing using the mixed etching solution of the sodium hydroxide (NaOH) and of the sodium hypochlorite (NaClO) has been investigated. The reaction rate during the texturing process is easier to control due to the presence of NaOCl as an oxidizing agent in NaOH solution. The advantage of this etching is that the uniform mc-Si surface texturing with a low step height and less grain boundary delineation can be obtained. The Mc-Si surface after NaOH-NaOCl mixed etching with the 1: 4 ratio in the case of 20% NaOH has the optimum light trapping effect. In the case of the optimum etching condition, the average reflectivity for the textured surface of a large area (156 × 156 mm2) mc-Si can be reduced to less than 10%.

Creating textured surfaces using plasma electrolysis

Abstract

Porous silicon/NaOH texturization surface treatment of crystalline silicon for solar cells

Crystalline silicon surface texturing is one of the important issues of modern silicon solar cells efficiency improvement. In this work an attempt has been made to obtain a well-textured multicrystalline silicon and monocrystalline silicon surface through two different approaches. The first with standard alkaline (NaOH) solution, the second is based on a combination of formed structures obtained in NaOH and stain etching treatment in acid (HF/HNO3/H2O) solution. effect of texturisation based on these two methods on the surface morphology of Si wafers as well as on the optical and optoelectronic properties are presented in this paper. Extensively study of the surface morphologies evolution of Si wafer has been carried out and correlate to the reflectance, the effective lifetime, the internal quantum efficiency (IQE) maps and current–voltage (I–V) characteristics change before and after surface treatment.

Highly textured multi-crystalline silicon surface obtained by dry etching multi-step process

In this work we propose the use of a plasma dry etching technique to condition the morphology of a silicon surface. The low environmental impacted NF3 halogen compound is adopted together with Ar to perform a multi-step process which helps to enhance the silicon surface texturing, thus reducing the time needed for the whole dry etching procedure, which also include saw damage removal on silicon wafers. A detailed study of surface reflectance and etching rate as a function of the dry plasma process parameters is discussed to achieve suitable multi-crystalline silicon surfaces for photovoltaic applications.

Femtosecond laser micromachining for optofluidic and energy applications

Femtosecond laser micromachining is a powerful and versatile tool both for the fabrication of photonic and optofluidic devices and for material surface processing. The basics of the technique will be discussed and some examples of applications will be presented. In particular, an optofluidic device for sensing applications, together with silicon surface texturing for applications in the fields of photovoltaic cells and photodetectors are discussed.

A comparative study based on optical and electrical performance of micro- and nano-textured surfaces for silicon solar cells

In this contribution, we report on the optical and electrical properties of textured silicon surfaces usually incorporated in solar cell fabrication. In order to study the influence of different texturisation processes, nano-texturing was accomplished by soft UV-NIL process while the micro-textured surfaces were prepared using TMAH solution. The nano-textured surfaces were found to be superior in terms of optical performance but the passivation of these structures was solely limited by the fabrication process itself. Any defect or damage caused during the pattern transfer (plasma etch) process acts as a recombination centre which significantly reduces carrier lifetime. By systematically removing the plasma induced damage from the surface, it was possible to improve the effective lifetime from 24.4μs to 1092μs. We report that, despite of the enlarged surface area compared to micro-textured surface, our nano-texture surface possess excellent optical properties and higher lifetime.

Antireflection properties of graphene layers on planar and textured silicon surfaces

In this study, theoretical and experimental investigations have been carried out to explore the suitability of graphene layers as an antireflection coating. Microwave plasma enhanced chemical vapor deposition and chemically grown graphene layers deposited on polished and textured silicon surfaces show that graphene deposition results in a large decrease in reflectance in the wavelength range of 300–650 nm, especially in the case of polished silicon. A Si3N4/textured silicon reference antireflection coating and graphene deposited polished and textured silicon exhibit similar reflectance values, with the graphene/Si surface showing lower reflectance in the 300–400 nm range. Comparison of experimental results with the finite difference time domain calculations shows that the graphene along with a SiO2 surface layer results in a decrease in reflectance in the 300–650 nm range, with a reflectance value of <5% for the case of graphene deposited textured silicon surfaces. The monolayer and inert character along with the high transmittance of graphene make it an ideal surface layer. The results of the present study show its suitability as an antireflection coating in solar cell and UV detector applications.

Response to “Comment on ‘The origins of pressure-induced phase transitions during the surface texturing of silicon using femtosecond laser irradiation’” [J. Appl. Phys. 113, 126102 (2013)

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Comment on “The origins of pressure-induced phase transitions during the surface texturing of silicon using femtosecond laser irradiation” [J. Appl. Phys. 112, 083518 (2012)

Smith et al. [Appl. Phys. 112, 083518 (2012)] have reported that the irradiation of Si (100) with femtosecond laser pulses of a sufficiently high fluence, about 4 kJ m−2, results in the formation of the Si-III and Si-XII phases in the irradiated region. These authors have also suggested that the formation of the Si-III and Si-XII phases is due to the pressure-induced phase transitions in the silicon. It is argued here that Smith et al. [Appl. Phys. 112, 083518 (2012)] have incorrectly assigned the observed Raman peaks at 354 and 395 cm−1 to the Si-XII phase and that these peaks are due to the Si-III phase.

Influence of surface texturing conditions on crystalline silicon solar cell performance

We carried out the surface texturing of crystalline silicon in alkaline solutions via anisotropic etching. We achieved random pyramids of about 10 μm in size. The size of these pyramids was then gradually reduced using a new solution. In this paper, we investigate the impact of the size of the pyramids on the emitter properties and the front electrode (Ag) contact. To make small (∼3.5 μm) and large (∼9.0 μm) pyramids, we controlled the texturing time and performed one-sided texturing using a silicon nitride film. We compared the formation and quality of a POCl3-diffused n+ emitter in a furnace for small and large pyramids by using SEM images and emitter saturation current density (J0e) measured Quasi-Steady-State Photo-Conductance (QSSPC). For a comparison, we carried out to simulated using TCAD simulator software (SILVACO, the Athena module). After metallization, we measured the Ag contact resistance via the transfer length method (TLM). We observed the surface distributions of the Ag crystallites using SEM images. We used light I–V to measure the performance of screen-printed solar cells. The efficiency of the solar cell in the case of the small and that in the case of the large pyramids improved by about 17.4% and 17.0%, respectively. We believe that differences in the emitter uniformity and the front Ag contact resistance resulted from this difference in the cell performance. Solar cells perform better when the pyramids are small.

Silicon surface texturing with a combination of potassium hydroxide and tetra-methyl ammonium hydroxide etching

A two step silicon surface texturing, consisting of potassium hydroxide (KOH) etching followed by tetra-methyl ammonium hydroxide etching is presented. This combined texturing results in 13.8% reflectivity at 600 nm compared to 16.1% reflectivity for KOH etching due to the modification of microstructure of etched pyramids. This combined etching also results in significantly lower flat-band voltage (VFB) (−0.19 V compared to −1.3 V) and interface trap density (Dit) (2.13 × 1012 cm−2 eV−1 compared to 3.2 × 1012 cm−2 eV−1).

The origins of pressure-induced phase transformations during the surface texturing of silicon using femtosecond laser irradiation

Surface texturing of silicon using femtosecond (fs) laser irradiation is an attractive method for enhancing light trapping, but the laser-induced damage that occurs in parallel with surface texturing can inhibit device performance. In this work, we investigate the light-material interaction during the texturing of silicon by directly correlating the formation of pressure-induced silicon polymorphs, fs-laser irradiation conditions, and the resulting morphology and microstructure using scanning electron microscopy, micro-Raman spectroscopy, and transmission electron microscopy. We show that raster scanning a pulsed laser beam with a Gaussian profile enhances the formation of crystalline pressure-induced silicon polymorphs by an order of magnitude compared with stationary pulsed fs-laser irradiation. Based on these observations, we identify resolidification-induced stresses as the mechanism responsible for driving sub-surface phase transformations during the surface texturing of silicon, the understanding of which is an important first step towards reducing laser-induced damage during the texturing of silicon with fs-laser irradiation.

Fabrication and characterization of monocrystalline-like silicon solar cells

Due to the necessity of associating high-purity monocrystalline silicon and lower-cost multicrystalline silicon wafers, the monocrystalline-like silicon technique is used as a promising method for solar-cell fabrication. The grain orientation of this material is composed of both 〈111〉 and 〈100〉 orientations. As a result of a combination for properties on the basis of two types of materials, silicon surface texturing was carried out by using alkaline (NaOH) chemical and reactive ion etching (RIE) texturing. In this research, we investigated the optical and the electrical properties of silicon surfaces prepared by using different texturing processes. By using the alkaline and RIE texturing processes, we obtained a fill factor of 78.6% with a conversion efficiency of 17.2% for a monocrystalline-like silicon wafer with an active surface area of 243 cm2. Compared to alkaline texturing, this conversion efficiency shows an increase of 0.5%. Thus, large-area monocrystalline-like silicon solar cells with high efficiency and low cost can be fabricated.

Green Texturing of Multi-crystalline Silicon Wafers using Acid Etching and Ultrasonic

Surface texturing of silicon can reduce the reflectance of incident light and hence increase the conversion efficiency of solar cells. Many approaches have been present in texturing silicon solar cell. As a practical method, chemical wet etching has been widely used in mono-crystalline silicon and multi-crystalline silicon (mc-Si), but the cost and high reflectance hamper its widely used. In this paper, a new approach is presented by using mixed acid with ultrasonic to texture mc-Si solar cell. Ultrasound transmitted in the acid solution can induce the cavitations and cavitations erosion, which can improve the texturing of mc-Si and yield regular morphology on the surface of mc-Si. In order to study the efficiency of new methods, a comparative experiment between mixed acid and mixed acid combined with ultrasound is designed to texture the surface of mc-Si with the same samples. A highspeed CCD with argon arc lamp is applied to observe the cavitations and cavitations erosion in texturing. The morphology images of the two textured mc-Si samples are obtained by scanning electron microscope (SEM), more holes and regular distributed morphology for the presented method are observed, which is yielded by comprehensive etching between acid and cavitations erosions. A spectrophotometer is used to measure the anti-reflectance of the mc-Si surface, and the reflectance of 10.2% is obtained on the surface of mc-Si textured by mixed acid combined with ultrasonic wave, which is much less than that of traditional acid etching.

Non-ablative texturing of silicon surface with a continuous wave fiber laser

Laser surface texturing based on ablation has been widely used, but hardly any reports can be found on non-ablative laser surface texturing. Silicon is highly transparent to the infrared wavelength of fiber laser (λ = 1090 nm) and thus regarded as an unsuitable tool for the purpose of surface texturing. However, we succeeded in using a continuous wave fiber laser to produce regular arrays of sub-micron bumps on silicon surface. The approach is shown to be based on laser-induced oxidation of silicon.

A simple method to produce dual-scale silicon surfaces for solar cells

In this paper, we report a simple method to produce micro/nano dual-scale textured silicon surfaces by combining alkaline etching with plasma surface processing. The surface morphologies were investigated by a field emission scanning electron microscope, while the surface reflectance and wettability were examined by a UV–VIS-NIR spectrophotometer and a drop shape analysis system, respectively. Results show that random nano-scale needle-like structures have been formed on micro-scale pyramids. The average reflectance and contact angle are 2.8% and ~120°, respectively. The solar cell based on the dual-scale textured silicon yields a high efficiency of 17.5% with a short circuit current density of 36.0mA/cm2.

A new approach for improving the silicon texturing process using gas-lift effect

A new cost-effective and efficient approach is proposed for texturing the crystalline silicon using the gas-lift effect (GLE). The advantages of this approach over the conventional ones are that significantly lower amounts of IPA is used and much shorter etching time is required to achieve the same reflectivity. GLE is generated by taking advantage of the hydrogen bubbles evolved between the silicon wafer being etched and a glass plate, placed in parallel, creating a gap of 1–2 mm. This effect then acts as a pumping mechanism detaching more bubbles from the silicon surface, accelerating them to the top and out of the system, as quickly as they are generated. Experiments were carried out with various combinations of TMAH/IPA concentrations for two different GLE conditions to analyse and determine their influence on etching time, etching rate, surface morphology and reflectivity of the textured silicon surface. The use of this new approach in surface texturing, allowed the reduction of the required IPA by 50% and etching time by more than 60% to achieve the same reflectivity. This can ultimately lead to a significant reduction in cost by increasing the efficiency of the texturing process. A combination of 3.5% IPA and 2 mm GLE resulted in a textured silicon surface having a low specular solar-weighted reflectivity of 0.15%.