Textured Silicon Research Articles

Enhancement of reflectance reduction of solar cells by a silicon nanoparticle layer on a textured silicon substrate

To reduce the surface reflectance of Si solar cells, a structure has been developed in which a silicon nanoparticle (SiNP) layer is formed on a pyramid-like structure to simultaneously exploit multiple reflections and refractive index changes. The high refractive index of Si leads to the high reflectance of polished Si wafers. A conventional pyramid-like structure is formed on the surface of the Si wafer to reduce reflections using multiple reflections; however, the resultant sample reflectance is high because of the refractive index difference between air and Si. Nevertheless, although the reflectance of a SiNP layer on a polished Si wafer is high, the short-wavelength reflectance is <10 %. Our SiNP layer was then formed on a textured Si wafer by spin coating with a succession of changes to the spin-coating speed. In this manner, the reflectance after each speed change drastically decreased to <10 %, while the short-circuit current increased from 25.2 to 34.1 mA cm−2. The extremely thin SiNP layer and pyramid-like structure are promising as antireflective layers for solar cells.

Comprehensive cell to module optical loss analysis of metal assisted chemically etched inverted pyramid textured multi-crystalline silicon solar cells and modules by ray-tracing method

Most of the recent articles addressing the texturing issues of diamond wire sawn multi-crystalline silicon (mc-Si) wafers propose metal-assisted chemical etching (MACE) inverted pyramid texturing scheme as the best suited industrial process for the fabrication of low-cost, high efficiency solar cells. However, a detailed generation loss analysis of such textured solar cells are not widely investigated yet, especially after module conversion. We present a comprehensive analysis of various optical losses in MACE inverted pyramid textured mc-Si solar cells and modules using the SunSolve module ray-tracer simulator from PV Lighthouse. The simulation model accurately predicted the optical properties of MACE inverted pyramid textured samples and the simulated reflectance values were nearly identical to experimentally measured values at different stages of solar cell processing (before and after ARC). This study quantifies and benchmarks the optical generation losses of not-encapsulated and encapsulated inverted pyramid textured cells with well established models of random pyramid textured and iso-textured solar cells for aluminum back surface field (Al-BSF) architecture. Moderate cell to module (CTM) generation current loss was noticed for inverted pyramid textured solar cells, which was nearly 0.71 mA-cm−2 lower than random pyramid textured and 1.05 mA-cm−2 higher than iso-textured solar cells. We find that adoption of MACE inverted pyramid texturing over acid texturing enhances the photo-generation in mc-Si modules by ∼0.5% and that the total photo-generation current density in mc-Si solar modules approach 99.6% of that in random pyramid textured c-Si modules.

Advanced antireflection for back-illuminated silicon photomultipliers to detect faint light

Silicon photomultipliers have attracted increasing attention for detecting low-density light in both scientific research and practical applications in recent years; yet the photon losses due to reflection on the light-sensitive planar silicon surface considerably limit its photon detection efficiency. Here we demonstrate an advanced light trapping feature by developing the multi-layer antireflection coatings and the textured silicon surface with upright random nano-micro pyramids, which significantly reduces the reflection of faint light in a wide spectrum, from ultraviolet to infrared. Integrating this advanced photon confinement feature into next-generation back-illuminated silicon photomultiplier would increase the photon detection efficiency with significantly lower reflection and much more active areas. This advanced design feature offers the back-illuminated silicon photomultiplier broader application opportunities exemplified in the emerging scenarios such as nuclear medical imaging, light detection and ranging for autonomous driving, detection of scintillation light in ionizing radiation, as well as high energy physics.

Exploring the superhydrophilicity of nanosecond laser textured silicon: a Raman analysis.

We present Raman analysis of nanosecond laser textured silicon. The samples have also been characterized by field emission scanning electron microscopy (FESEM) and x ray diffraction. Contact angles (CAs) are measured to trace the hydrophilic nature. Characterization of the textured samples in argon and air shows that cleavage cracks are developed during texturing. CA measurements reveal the superhydrophilic nature of textured samples obtained in the presence of ambient oxygen and argon. In vacuum, however, the hydrophilicity is decreased. Micro-Raman analysis indicates the formation of nano-sized cleavage cracks that impart stable superhydrophilic properties to textured silicon is supported from FESEM images also. On the other hand, in vacuum textured silicon, evidence of such cracks is not noticed, which is also supported by Raman analysis. Further, the hydrophilicity is decreased. A definitive trend appears to exist between Raman signatures and hydrophilicity. We believe that the study will further the understanding of the mechanistic aspect in designing textured silicon with a high degree of self-cleaning capability.

Light trapping PMMA planar ridged waveguide on a laser textured silicon substrate for ultra-low reflectivity

A novel composite total internal reflectance fiber structure on monocrystalline silicon (mono c-Si) constructed by specific micro-structures with base angle of 55 degrees and closely nested PMMA film is innovatively proposed to achieve a more effective sunlight trap for the first time. Besides the trapped light caused by multiple reflections on the laser textured surface, the total internal reflectance effect of light on the exiting surface of PMMA film is realized, which gains more times of reflection and absorption among the composite structure and further improves the anti-reflection effect. It’s found the reflectivities of the composite structures containing regular pyramid and V-shaped micro-structures have notably decreased to under 1.45% and 2.60% respectively in wavelength range of 350–1000 nm. This composite structure provides a new alternative and effective approach for the design and fabrication of silicon surface with ultra-low reflectivity.

Emitter formation with boron diffusion from PECVD deposited boron-doped silicon oxide for high-efficiency TOPCon solar cells

We present a systematic study of emitter formation with dopant diffusion from boron (B)-doped hydrogenated silicon oxide (a-SiOx:H) deposited on textured n-type monocrystalline silicon (n-c-Si) wafers using a 13.56 MHz plasma-enhanced chemical vapor deposition (PECVD) system. The B atoms in the a-SiOx:H are activated and diffused into the n-c-Si wafer during a high-temperature annealing to form a p/n junction for solar cell application. Afterward, the B-doped SiOx layer is removed by hydrofluoric acid selective etching to obtain a clean surface for the deposition of AlOx passivation and SiNx antireflection layers. With the optimization of the PECVD deposition and the following annealing/etching processes, the B diffused region with a sheet resistance of 60–100 Ω/sq and a junction depth of 1.2–1.5 μm is obtained. A champion implied open-circuit voltage (iVoc) of 705 mV and a single-side saturated recombination current density (J0,s) of 17.6 fA/cm2 are obtained from a double-sided B diffused sample after the passivation with an atomic-layer-deposition (ALD) AlOx. In addition, the contact resistivity (ρc) at the metal/emitter interface is lower than 5 mΩcm2, where the metal contact is a Ti/Pd/Ag tri-layer structure. All of the material properties meet the requirements of high-efficiency solar cell. With the optimized emitter in the front, we made a SiOx and heavily phosphorus-doped polycrystalline silicon carbide (n-poly-SiCx) stack on the rear surface to form tunnel oxide passivated contact (TOPCon) solar cells. The results show that the iVoc of semi-finished TOPCon solar cell before metallization is more than 725 mV. Finally, a TOPCon solar cell with an efficiency of 24.24% is obtained, which is comparable with the TOPCon solar cells with the industrial thermally diffused emitter.

Molecular dynamics simulations of friction behaviours on nano-textured silicon surfaces

ABSTRACT Molecular dynamics simulations have been applied to study the friction behaviours of nano-textured silicon surfaces. The effects of texture shape, texture pitch and indenter size on forces, temperature, stress and plastic deformation are investigated. It is found that the presence of the texture facilitates the reduction of friction due to the decrease the contact area. The texture shape significantly influences the tribological properties of the textured surface. The hemispherical texture has the optimum friction reduction effect, followed by cylindrical texture and lastly by cubic texture. The number of atoms that undergo phase transformation in the scratching is the maximal for the cubic texture while the smallest for the hemispherical texture. However, the texture pitch has little effect on the tribological properties of the textured surface. In addition, it is interesting to observe the indenter size effect that a larger indenter causes a smaller force and wear volume at the initial stage of scratching. The indenter size effect on tribological properties results from the variation of contact area in the scratching. The insights gained can shed light on the friction mechanism of nanoscale textured silicon surface and are beneficial to the design of micro/nanoscale devices such as micro/nanoelectromechanical systems with surface textures.

Energy yield modelling of textured perovskite/silicon tandem photovoltaics with thick perovskite top cells.

Recent advances in solution processing of micrometer-thick perovskite solar cells over textured silicon bottom solar cells allowed a new promising approach for the fabrication of 2T perovskite/silicon tandem photovoltaics, combining optimal light management in the textured bottom cell with the ease of solution processing. Detailed simulations are needed to assess the performances of this morphology configuration (thick perovskite configuration). In this work, in-depth optical and energy yield (EY) simulations are performed to compare the thick perovskite configuration with other relevant morphology configurations for 2T perovskite/silicon tandem photovoltaics. Under standard test conditions, the total photogenerated current of the thick perovskite configuration is 1.3 mA cm-2 lower (-3.4% relative) than the one of the conformal perovskite on textured silicon configuration for non-encapsulated cells and only 0.8 mA cm-2 (-2.1% relative) for encapsulated cells. Under realistic outdoor conditions, EY modelling for a wide range of locations shows that, while conformal perovskite on textured silicon configuration remains the optimal configuration, thick perovskite configuration exhibits a mere ∼2.5% lower annual EY. Finally, intermediate scenarios are investigated with the angle of the perovskite front-side texture differing from the silicon texture and critical angles for efficient light management in these configurations are identified.

Atomic simulation of textured silicon carbide surface ultra-precision polishing

In view of increasing accuracy requirements and difficult machining characteristics of silicon carbide materials, this paper proposes new machining method with ultra-high precision. Based on improvement of ultra-precision machining quality by textured surface, specific nano texture was machined on silicon carbide surface. Effects of different texture parameters on polishing force, polishing temperature, potential energy, dislocation, stress and friction coefficient were analyzed. Two typical textures (grooves and pits) with different sizes were compared. Simulation results show that surface morphology, polishing force and friction coefficient are improved with the increase in groove depth and pit depth. The smaller the groove spacing, the better the polishing quality and polishing behavior. In addition, groove texture can effectively inhibit the growth of dislocations and defect atoms during polishing. Compared with non-textured surface, textured silicon carbide surface can improve polishing conditions. It is found that groove texture has more beneficial effect on polishing quality than pit texture with the same size.

Role of Scanning Speed in Morphological and Optical Properties of Nanosecond Laser Textured Silicon Surfaces

Laser surface texturing (LST) is a rapid single-step method for surface functionalization. Different micro and nanoscale structures can be fabricated by controlling the laser parameters, ambient conditions, and material properties. In this work, we investigated the role of laser scanning speed in the morphological and optical properties of nanosecond laser textured silicon surfaces. Keeping the laser flounce just above the threshold, we controlled the laser scanning speed in the range 50-100 μm/s to monitor the morphological and optical changes. Morphological analysis shows various randomly arranged microstructures in the processed area, and the induced structures strongly depend on the scanning speed. The total reflection spectrum (specular+diffuse) from laser textured silicon shows that a significant reduction (≈60%) in reflectivity is possible with the decrease in scanning speed from 100 μm/s to 50 μm/s. These highly absorptive and large-area microstructures have numerous possibilities in photovoltaics, optoelectronic devices, and other material science applications.

Scaled Deposition of Ti3C2Tx MXene on Complex Surfaces: Application Assessment as Rear Electrodes for Silicon Heterojunction Solar Cells.

Two-dimensional transition metal carbides (MXenes) are of great interest as electrode materials for a variety of applications, including solar cells, due to their tunable optoelectronic properties, high metallic conductivity, and attractive solution processability. However, thus far, MXene electrodes have only been exploited for lab-scale device applications. Here, to demonstrate the potential of MXene electrodes at an industry-relevant level, we implemented a scalable spray coating technique to deposit highly conductive (ca. 8000 S/cm, at a ca. 55 nm thickness) Ti3C2Tx films (Tx: surface functional groups, i.e., −OH, −O, −F) via an automated spray system. We employed these Ti3C2Tx films as rear electrodes for silicon heterojunction solar cells as a proof of concept. The spray-deposited MXene flakes have formed a conformal coating on top of the indium tin oxide (ITO)-coated random pyramidal textured silicon wafers, leading to >20% power conversion efficiency (PCE) over both medium-sized (4.2 cm2) and large (243 cm2, i.e., industry-sized 6 in. pseudosquare wafers) cell areas. Notably, the Ti3C2Tx-rear-contacted devices have retained around 99% of their initial PCE for more than 600 days of ambient air storage. Their performance is comparable with state-of-the-art solar cells contacted with sputtered silver electrodes. Our findings demonstrate the high-throughput potential of spray-coated MXene-based electrodes for solar cells in addition to a wider variety of electronic device applications.

Silicone-induced granuloma of breast implant capsule mistaken for breast implant-associated anaplastic large cell lymphoma

For patients with breast implants who present with an isolated seroma, capsular contracture, or peri-implant mass, clinicians must rule out breast implant-associated anaplastic large cell lymphoma (BIA-ALCL). As non-malignant silicone-induced granuloma of breast implant capsule (SIGBIC) may mimic BIA-ALCL, particular care must be exercised to prevent misdiagnosis. In this report, we describe three cases of SIGBIC misdiagnosed as BIA-ALCL. In each of these cases, a preoperative evaluation including breast magnetic resonance imaging and physical examination, as well as the fact that a textured silicone implant was used in the patients, indicated a high probability of malignancy. In all three cases, however, an explorative operation and pathologic results revealed foreign body granulomas without malignant features. While it is critical that potential cases of BIA-ALCL be diagnosed and treated quickly, hasty judgments may lead to misdiagnosis and severe emotional distress in patients. Increased awareness of SIGBIC, specifically its mimicry of BIA-ALCL, may be helpful to avoid these outcomes.

Silicone-induced granuloma of breast implant capsule mistaken for breast implant-associated anaplastic large cell lymphoma

For patients with breast implants who present with an isolated seroma, capsular contracture, or peri-implant mass, clinicians must rule out breast implant-associated anaplastic large cell lymphoma (BIA-ALCL). As non-malignant silicone-induced granuloma of breast implant capsule (SIGBIC) may mimic BIA-ALCL, particular care must be exercised to prevent misdiagnosis. In this report, we describe three cases of SIGBIC misdiagnosed as BIA-ALCL. In each of these cases, a preoperative evaluation including breast magnetic resonance imaging and physical examination, as well as the fact that a textured silicone implant was used in the patients, indicated a high probability of malignancy. In all three cases, however, an explorative operation and pathologic results revealed foreign body granulomas without malignant features. While it is critical that potential cases of BIA-ALCL be diagnosed and treated quickly, hasty judgments may lead to misdiagnosis and severe emotional distress in patients. Increased awareness of SIGBIC, specifically its mimicry of BIA-ALCL, may be helpful to avoid these outcomes.

Damage and residual layer analysis of reactive ion etching textured multi-crystalline silicon wafer for application to solar cells

As part of the surface texturing process of multi-crystalline silicon solar cells, isotropic etching is performed by using an acidic solution. Furthermore, metal catalyst chemical etching (MCCE), reactive ion etching (RIE), and laser etching are used to further decrease surface reflectance. This study aimed to increase the power conversion efficiency of the solar cell by improving the short-circuit current density (Jsc) using MCCE and RIE. During RIE, a byproduct and a plasma damage layer are formed on the silicon surface, which decrease the efficiency of the solar cell and therefore need to be identified and effectively removed. Transmission electron spectroscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses were performed to identify the byproducts formed during RIE to confirm that it was amorphous silicon oxide. Furthermore, an etching process using acidic and alkaline base solutions was used to remove the plasma damage layer and the Jsc loss was calculated using the reflectance. As a results, confirm a difference of up to ∼ 1.6 mA/cm2, and an improvement of approximately 0.6% was observed in the solar cell efficiency. These results show a method of minimizing Jsc loss and removing surface damage in a silicon solar cells fabricated using the RIE method.

20% efficiency mg/PCBM/p-type silicon hybrid solar cells

Silicon/organic hybrid solar cells, with relatively simple and low-energy consumption fabrication processes, hold the promise for over-all cost reduction. However, their performances are still not comparable to the commercial crystalline silicon (c-Si) solar cells. Here, hybrid devices with organic phenyl-C61-butyric acid methyl ester (PCBM) layer inserted between metal electrode and textured p-type crystalline silicon (c-Si(p)) substrate are investigated. The quality of the PCBM/c-Si(p) contact is much improved after a SiOx thin layer is formed on the a-Si:H(i) surface and a Voc of 706 mV and an efficiency of 20.0% are achieved on the hybrid solar cells. Analysis of the dark J-V-T characteristics of the hybrid device shows that the junction current is dominated by the minority-carrier diffusion current.

The optical performance of random and periodic textured mono crystalline silicon surfaces for photovoltaic applications

Surface textures that result in high optical yields are crucial for high efficiency photovoltaic (PV) devices. In this work three different texturing approaches are presented that result in smooth concave structures devoid of sharp features. Such features can sustain the crack-free growth of device quality nano- to poly-crystalline materials such as nano-crystalline silicon, perovskites or C(I)GS, facilitating routes towards hybrid multijunction PV devices. A sacrificial implanted poly-c-Si layer is used to develop a random surface texture for the first texturing approach (Tsac). The influence of the processing conditions, such as layer thickness, implantation energy, dose and ion type, annealing time and temperature, of the sacrificial layer on the developed surface features is investigated. Additionally, a photolithographically developed honeycomb texture (Thoney) is presented. The influence of mask design on the honeycomb features is discussed and a relation is established between the honeycomb period and crack formation in nano-crystalline silicon layers. The reflective properties (spectral reflection, haze in reflection and angular intensity distribution) of these approaches are characterized and compared to a third texturing approach, Tsp, the result of chemically smoothened pyramidal &lt;111&gt; features. It was demonstrated that high optical scattering yields can be achieved for both Thoney and Tsp. Additionally, the performance of a-Si/nc-Si tandem devices processed onto the different textures is compared using both optical device simulations and real device measurements. Simulations demonstrate strong improvements in Jsc-sum (≈45%), in reference to a flat surface, and high Voc*FF of over 1 V are demonstrated for Tsp.

Fat Grafting before Delayed Prophylactic Mastectomy and Immediate Implant Reconstruction for Patients at High Risk of Complications.

The majority of patients undergoing bilateral prophylactic mastectomy request immediate implant-based breast reconstruction. Some patients, especially those with prior radiotherapy, are at increased risk of early cutaneous complications and implant loss. The authors developed the technique of primary fat grafting before delayed prophylactic mastectomy to minimize early complications for selective high-risk patients. They have completed 21 cases in 14 patients, 10 of whom had previous lumpectomy and radiation treatment for breast cancer. A single session of fat grafting, with a median injection volume of 250 ml (interquartile range, 200 to 300 ml), was performed a median period of 19 weeks (interquartile range, 16 to 28 weeks) before prophylactic mastectomy. All cases were direct-to-implant reconstruction using textured silicone implants. The median implant volume was 410 ml (interquartile range, 318 to 450 ml). A minor early complication developed in 14 percent of cases (three of 21), with no early implant loss. At a median follow-up of 9 months (interquartile range, 5 to 27 months), the authors found no cases of implant loss and an excellent or good aesthetic outcome (score of 5 or 4) in 16 of 21 cases (76 percent). Fat grafting before prophylactic mastectomy is a novel strategy to minimize early complications and avoid implant loss in patients at high risk of postoperative complications. . Therapeutic, IV.

Hybrid-structured air-stable solar selective absorber on flexible textured silicon

A kind of air-stable hybrid-structured solar selective absorber (hs-SSA) with enhanced thermal stability is prepared by combining ultra-thin textured silicon (ut-Si) with cermet coating. The ut-Si obtained by the wafer thinning and fast texturization method shows excellent flexibility and light-trapping ability. Then the W-WOx coatings are deposited onto the ut-Si substrate in a spreading manner on the pyramid-like structure. The as-deposited hs-SSA exhibits good light-harvesting capability with spectral selectivity (α/ε) of 0.968/0.340. Additionally, the ut-Si shows its superiority in oxidation resistance and chemical stability compared with the traditional metal substrate. After 120-h air-annealing at 250 °C and 72-h vacuum-annealing at 500 °C, the performance losses are within a tiny and reasonable range, showing excellent chemical, structural and optical stability, exhibiting excellent application potential in medium-temperature solar harvesting field.

Thermal Stability of the Copper and the AZO Layer on Textured Silicon

Transparent conductive oxide (TCO) film is the most widely used front electrode in silicon heterojunction (SHJ) solar cells. A copper metallization scheme can be applied to the SHJ process. The abundance of zinc in the earth’s crust makes aluminum-doped zinc oxide (AZO) an attractive low-cost substitute for indium-based TCOs. No work has focused on the properties of the copper and AZO layers on the textured silicon for solar cells. This work deposited an aluminum-doped zinc oxide layer and copper metal layer on textured (001) silicon by a sputtering to form Cu/AZO/Si stacks. The structures of Cu/AZO/Si are characterized by scanning electron microscope (SEM), scanning transmission electron microscope (STEM), and energy-dispersive X-ray spectrometer (EDS). The results show that the copper thin film detached from AZO in the valley of the textured silicon substrate at a temperature of 400 °C. Additionally, the gap between the copper and AZO layers increases as temperature increases, and the 65 nm thickness AZO layer was found to be preserved up to 800 °C.

Comprehensive device simulation of 16.9% efficient two-terminal PbS–PbS CQD tandem solar cell

The significant losses that limit the efficiency of a single-junction solar cell are thermalization loss and transmission loss. Thus, to efficiently utilize the solar spectrum and mitigate these losses, tandem solar cells (TSCs) have significantly impacted the photovoltaic (PV) landscape. In this context, the research on perovskite/silicon tandems is currently dominating the research community. However, challenges such as stability of perovskite, pin-hole defects, conformal deposition of perovskite over textured silicon, the low absorption coefficient of silicon, and high module cost of the bottom subcell are the tailback for its mass production at the industrial level. Therefore, considering the detailed balance limit for the TSC, a low-cost solution-processed top and bottom subcells with a tunable bandgap can be well thought for the low-cost tandem design. Thus, here in this work, two different PbS–PbS colloidal quantum dot (CQD) TSCs with a conversion efficiency of 15.6% and 16.9% are proposed through comprehensive device simulations. Three different PbS-CQDs with a bandgap of 1.14eV, 1.45eV, and 1.56eV are utilized to design the TSCs under consideration. Detailed standalone and tandem analysis has been carried out in terms of absorber layer thickness variation, filtered spectrum, filtered integrated power, current matching, tandem current density voltage (J-V) curves, and tandem PV parameter to finalize the conversion efficiency. The filtered spectrums are obtained by using the transfer matrix method to account for the interfacial reflection losses and thin-film interference effects. The tandem device constructed using 1.45eV and 1.56eV based top subcell showed the open-circuit voltage V OC of as high as 1.71V and 1.83V, respectively. The comprehensive theoretical analysis of PbS–PbS CQD tandem devices proposed in this work may pave the way for developing high-efficiency TSCs for low-cost applications. • Two different PbS–PbS CQDs tandem solar cells (TSCs) with a conversion efficiency of 15.60% and 16.92% are proposed. • Detailed standalone and tandem analysis has been carried out to optimize the conversion efficiency. • Three different PbS-CQDs with a bandgap of 1.14eV, 1.45eV, and 1.56eV are utilized to design the TSCs under consideration. • TSCs constructed using 1.45eV and 1.56eV based top subcell showed the open-circuit voltage V OC of 1.71V and 1.83V, respectively. • This detailed study would open path for development of high-efficiency, low-cost perovskite-PbS CQD TSCs in future.