Amorphous Silicon Research Articles

Novel Passivation and Gettering Strategy for Silicon Wafer by Al2O3/n‐poly‐Si/SiOx Stack for High‐Efficiency p‐Type Passivating Tunnel Oxide Contact Solar Cells

This study focuses on the enhanced passivation and gettering of boron‐doped p‐type solar grade silicon wafers by incorporating carrier‐selective and passivating tunnel oxide contact (TOPCon). A symmetrical stack of aluminum oxide (Al2O3)/p‐doped n‐type polysilicon (n‐poly‐Si)/ ultrathin silicon oxide (SiOx) in conjunction with long cycles of forming gas annealing is used for enhancing the silicon wafer quality with a novel approach. Multilayer of n‐poly‐Si/SiOx on p‐type crystalline silicon wafer exhibits an implied open‐circuit voltage (iVoc) of 726 mV, effective carrier lifetime (τeff) of 857 μs, and a low recombination current density (Jo) of 1.9 fA cm−2 when subjected to a postdeposition annealing (PDA) of phosphorus‐doped hydrogenated amorphous silicon (n‐a‐Si:H) at 820 °C. To boost passivation and gettering quality, 10 nm‐thick Al2O3 layers on both sides of n‐poly‐Si/SiOx samples are added. This leads to improved τeff (962 μs), reduced Jo (1.1 fA cm−2), and higher iVoc (728 mV). Herein, a thinner 50 nm n‐poly‐Si layer for improved properties is applied. The experiments show improved passivation and gettering. A Quokka‐3 simulation examines the potential of high‐efficiency p‐type TOPCon cells. A novel solar‐grade p‐type wafer quality enhancement approach is introduced, amalgamated with Quokka‐3 results, which could be a milestone in high‐efficiency p‐type TOPCon solar cell production.

Raman-based mapping and depth-profiling of the relaxation state in amorphous silicon

We show that the micro-scale variations in the relaxation state of amorphous silicon (a-Si) can be well-identified by Raman mapping over hundreds or thousands of μm2 in 1–2 h. Pure and relaxed a-Si is obtained by self-implantation in crystalline silicon (c-Si) followed by anneal at 500 °C. It is then locally re-implanted over micro-sized patterns to produce unrelaxed a-Si zones. Raman mappings are obtained by pointwise confocal μ-Raman and hyperspectral Raman imaging. We also measure the depth profiles of the relaxation state in re-implanted a-Si by scanning the edge of a re-implanted sample. We infer from the depth profiles that the minimal damage dose to fully de-relax a-Si is 0.04 displacements per atoms, which is an order of magnitude smaller than the fluence needed to fully amorphize c-Si.

Easy-to-Use Chemiluminescent-Based Assay for a Rapid and Low-Cost Evaluation of the Antioxidant Activity of Cosmetic Products

New cosmetic formulations are continuously requested by the market and the ingredients are constantly evolving. Recently the use of antioxidants has gained success and, in this context, analytical methods able to quickly and easily assess the antioxidant activity of cosmetics would make it possible to carry out analyses on new formulations even within the manufacturing process without the need for specialized laboratories and personnel, thus evaluating directly on-site the effectiveness and the shelf life of products. In this work, a chemiluminescent inhibition assay was developed for determining the total antioxidant activity in cosmetic products. The method was based on the luminol/enhancers/hydrogen peroxide/horseradish peroxidase chemiluminescent system, which generates light signals measurable through simple and compact instrumentation. The formation of the chemiluminescent signal is inhibited by the presence of antioxidant substances while it is restored once all the antioxidant molecules have been oxidized. The time of appearance of the light signal is related to the total antioxidant activity. The assay was carried out exploiting an integrated device comprising a microwell plate coupled with an array of amorphous silicon hydrogenated photosensors enclosed in a mini-dark box. The method was optimized in terms of concentrations and volumes of the required reagents and sample pre-treatment. A calibration curve was generated taking as a reference the antioxidant activity of ascorbic acid obtaining a detection limit of 10 µM. The developed method was applied to cosmetic products currently on the market as well as on spiked samples in order to evaluate the performance of the methods in terms of sensitivity, accuracy, and reproducibility.

Evaluating the Practical Efficiency Limit of Silicon Heterojunction–Interdigitated Back Contact Solar Cells by Creating Digital Twins of Silicon Heterojunction Solar Cells with Amorphous Silicon and Nanocrystalline Silicon Hole Contact Layers

Improving power conversion efficiency (PCE) in photovoltaics has driven innovative approaches in solar cell design and technology. Silicon heterojunction (SHJ) solar cells exhibit advantages in PCE due to their effective passivating contact structures. SHJ–interdigitated back contact (SHJ–IBC) solar cells have the potential to surpass traditional SHJ cells, attributed to their advantage in short‐circuit current (JSC). Herein, Silvaco Atlas technology computer‐aided design is used to create digital twins of high‐efficiency SHJ solar cells with amorphous silicon and nanocrystalline silicon hole selective contact (HSC) layers. Using parameters from digital twins of SHJ solar cells, the practical efficiency limit of SHJ–IBC solar cells is assessed. The results show that SHJ–IBC cells can achieve potential efficiencies of 27.01% with amorphous HSC and 27.38% with nanocrystalline HSC. Further efficiency augmentation to 27.51% can be achieved by narrowing the gap from 80 to 20 μm. This study not only advances comprehension of SHJ–IBC solar cells but also provides insights into optimizing geometrical configurations for improved performance. The utilization of digital twins provides a valuable tool for predicting and evaluating the performance of SHJ–IBC solar cells, contributing substantively to the ongoing development of high‐efficiency photovoltaic technology.

Dual-Band All-Optical Logic Gates by Coherent Absorption in an Amorphous Silicon Graphene Metasurface.

The dual-band polarization-independent all-optical logic gate by coherent absorption effect in an amorphous silicon (a-Si) graphene metasurface is investigated theoretically and numerically. Taking the substrate effect into consideration, the coherent perfect absorption condition of the a-Si graphene metasurface is derived on the basis of the Cartesian multipole method. The coherent nearly perfect absorption of the a-Si graphene metasurface is realized by the interference of multipole moments and the interband transition of monolayer graphene, achieving peak values of 91% and 92% at 894.5 nm and 991.5 nm, respectively. The polarization independence of the coherent absorption is revealed due to the center symmetry of the structure of the a-Si graphene metasurface. The dual-band polarization-independent all-optical XOR and OR logic gates are implemented at 894.5 nm and 991.5 nm by the a-Si graphene metasurface based on the coherent nearly perfect absorption, which has the opportunity to be utilized in all-optical computing, all-optical data processing, and future all-optical networks.

All‐Dielectric High‐Q Dynamically Tunable Transmissive Metasurfaces

AbstractActive metasurfaces, which are arrays of actively tunable resonant elements, can dynamically control the wavefront of the scattered light at a subwavelength scale. To date, most active metasurfaces that enable dynamic wavefront shaping operate in reflection. On the other hand, active metasurfaces operating in transmission are of considerable interest as they can readily be integrated with chip‐scale light sources, yielding ultra‐compact wavefront shaping devices. Here, designs for all‐dielectric low‐loss active metasurfaces which can dynamically manipulate the transmitted light wavefront in the near‐infrared wavelength range are reported. The active metasurfaces feature an array of amorphous silicon (a‐Si) pillars on a silica (SiO2) substate, which support resonances with quality factors (Q‐factors) as high as 9800. The high‐Q resonance dips observed in transmission can be transformed into transmission resonance peaks by positioning a‐Si pillar resonators at a prescribed distance from a crystalline Si substrate. The design of metasurface geometry with realistic interconnect architectures that enable thermo‐optic dynamic beam switching with switching times as low as 7.3 µs is reported. Beam switching is observed for refractive index differences between neighboring metasurface elements as low as 0.0026. It is shown that the metasurface structures with realistic interconnect architectures can be used for dynamic beam steering.

Bi-LSTM, GRU and 1D-CNN models for short-term photovoltaic panel efficiency forecasting case amorphous silicon grid-connected PV system

Photovoltaic (PV) panels stand as a prominent solution to meet the world's growing energy demands, due to their resistance to hard climate conditions, low-cost maintenance, and long lifetime. Nonetheless, the integration of PV power into electrical grids poses a significant challenge due to its inherent intermittency. This study aims to forecast future PV power based on historical records using Bidirectional Long Short-Term Memory (Bi-LSTM), One-Dimensional Convolutional Neural Network (1D-CNN), and Gated Recurrent Unit (GRU). Various performance metrics have been used to evaluate and compare the accuracy of the three models, including mean squared error, root mean squared error, mean absolute error, max error and R-squared for evaluation. The prediction of power photovoltaic based on the values registered in the last hour was carried out. Two scenarios have been investigated, with and without nighttime values to fit the models. Results reveal that the three forecasting models provide exceptional accuracy, achieving a correlation coefficient range of 96.9–97.2% for daytime PV power prediction in both scenarios, indicating a promising potential for these DNNs forecasters for optimizing energy production and improving overall PV system efficiency. The GRU, and BiLSTM-based forecasters showed identical results in terms of RMSE, MSE and MAE in both scenarios, while the 1D-CNN based forecaster showed accurate results in the second scenario, However, despite this improvement, it still falls behind forecasters based on Bi-LSTM or GRU in both scenarios.

Polarization-separating Alvarez metalens.

The rapid advancements in optical communication technologies have highlighted traditional optical components' limitations, particularly in size, adaptability, and integration capabilities, underscoring the need for more compact and versatile solutions. Metalenses offer a promising pathway to address these challenges, with their ability to provide high-functionality, miniaturized optical components. We developed a varifocal metalens with a polarization separation function designed for the wavelength of 1550 nm for potential application for next-generation communication technologies. To integrate the varifocal and polarization separation functions, polarization-dependent phase profiles for an off-axis Alvarez lens were derived and encoded by amorphous silicon pillar meta-atoms with rectangular cross sections to provide independent 0-2π phase delays for both orthogonal linear polarization components. The fabricated metalens achieved a varifocal range of 0.75 mm to 10.65 mm and a polarization extinction ratio of 18.5 dB.

Optical Sensing Using Hybrid Multilayer Grating Metasurfaces with Customized Spectral Response

Customized metasurfaces allow for controlling optical responses in photonic and optoelectronic devices over a broad band. For sensing applications, the spectral response of an optical device can be narrowed to a few nanometers, which enhances its capabilities to detect environmental changes that shift the spectral transmission or reflection. These nanophotonic elements are key for the new generation of plasmonic optical sensors with custom responses and custom modes of operation. In our design, the metallic top electrode of a hydrogenated amorphous silicon thin-film solar cell is combined with a metasurface fabricated as a hybrid dielectric multilayer grating. This arrangement generates a plasmonic resonance on top of the active layer of the cell, which enhances the optoelectronic response of the system over a very narrow spectral band. Then, the solar cell becomes a sensor with a response that is highly dependent on the optical properties of the medium on top of it. The maximum sensitivity and figure of merit (FOM) are SB = 36,707 (mA/W)/RIU and ≈167 RIU−1, respectively, for the 560 nm wavelength using TE polarization. The optical response and the high sensing performance of this device make it suitable for detecting very tiny changes in gas media. This is of great importance for monitoring air quality and thecomposition of gases in closed atmospheres.

Interfacial structure changes between amorphous silicon anode/liquid electrolyte using a highly dense and flat model electrode

Changes in the interfacial structures of the amorphous silicon (a-Si) anode/organic electrolyte interfaces in lithium-ion batteries were investigated using highly dense a-Si films fabricated by cathodic arc plasma deposition as a model electrode. Raman spectroscopy, transmission electron microscopy (TEM), and X-ray reflectivity revealed that the Si films were grown in an amorphous state with an atomically flat surface. The a-Si films exhibited lithium alloying and de-alloying reactions, with a large irreversible capacity during the first cycle. The irreversible capacity was derived from the formation of a solid electrolyte interphase (SEI) along with an incompletely de-alloyed Li-Si phase, as confirmed by ex situ TEM and X-ray photoelectron spectroscopy observations. The discharge and charge capacities of the Si films gradually decreased in the subsequent cycles, despite the fact that no further SEI formation or cracking of the Si layer occurred. Scanning electron microscopy observations combined with energy-dispersive X-ray spectroscopy revealed the miniaturization of the a-Si film in the surface region to generate domains measuring less than a few hundred nanometers. These results suggest that delamination and miniaturization of the a-Si nanodomains from the electrode surface are partly responsible for degradation of the a-Si anode.

Microwave characterization of tantalum superconducting resonators on silicon substrate with niobium buffer layer

Tantalum thin films sputtered on unheated silicon substrates are characterized with microwaves at around 10 GHz in a 10 mK environment. We show that the phase of tantalum with a body-centered cubic lattice (α-Ta) can be grown selectively by depositing a niobium buffer layer prior to a tantalum film. The physical properties of the films, such as superconducting transition temperature and crystallinity, change markedly with the addition of the buffer layer. Coplanar waveguide resonators based on the composite film exhibit significantly enhanced internal quality factors compared with a film without the buffer layer. The internal quality factor approaches 2 × 107 at a large-photon-number limit. While the quality factor decreases at the single-photon level owing to two-level system (TLS) loss, we have deduced that one of the causes of TLS loss is the amorphous silicon layer at the film–substrate interface, which originates from the substrate cleaning before the film deposition rather than the film itself. The temperature dependence of the internal quality factors shows a marked rise below 200 mK, suggesting the presence of TLS–TLS interactions. The present low-loss tantalum films can be deposited without substrate heating and thus have various potential applications in superconducting quantum electronics.

SiONx Coating Regulates Mesenchymal Stem Cell Antioxidant Capacity via Nuclear Erythroid Factor 2 Activity under Toxic Oxidative Stress Conditions.

Healing in compromised and complicated bone defects is often prolonged and delayed due to the lack of bioactivity of the fixation device, secondary infections, and associated oxidative stress. Here, we propose amorphous silicon oxynitride (SiONx) as a coating for the fixation devices to improve both bioactivity and bacteriostatic activity and reduce oxidative stress. We aimed to study the effect of increasing the N/O ratio in the SiONx to fine-tune the cellular activity and the antioxidant effect via the NRF2 pathway under oxidative stress conditions. The in vitro studies involved using human mesenchymal stem cells (MSCs) to examine the effect of SiONx coatings on osteogenesis with and without toxic oxidative stress. Additionally, bacterial growth on SiONx surfaces was studied using methicillin-resistant Staphylococcus aureus (MRSA) colonies. NRF2 siRNA transfection was performed on the hMSCs (NRF2-KD) to study the antioxidant response to silicon ions. The SiONx implant surfaces showed a >4-fold decrease in bacterial growth vs. bare titanium as a control. Increasing the N/O ratio in the SiONx implants increased the alkaline phosphatase activity >1.5 times, and the other osteogenic markers (osteocalcin, RUNX2, and Osterix) were increased >2-fold under normal conditions. Increasing the N/O ratio in SiONx enhanced the protective effects and improved cell viability against toxic oxidative stress conditions. There was a significant increase in osteocalcin activity compared to the uncoated group, along with increased antioxidant activity under oxidative stress conditions. In NRF2-KD cells, there was a stunted effect on the upregulation of antioxidant markers by silicon ions, indicating a role for NRF2. In conclusion, the SiONx coatings studied here displayed bacteriostatic properties. These materials promoted osteogenic markers under toxic oxidative stress conditions while also enhancing antioxidant NRF2 activity. These results indicate the potential of SiONx coatings to induce in vivo bone regeneration in a challenging oxidative stress environment.

Testing the effect of semi-transparent spectrally selective thin film photovoltaics for agrivoltaic application: A multi-experimental and multi-specific approach

The integration of photovoltaic technologies within the agricultural framework, known as agrivoltaics, emerges as a promising and sustainable solution to meet the growing global demands for energy and food production. This innovative technology enables the simultaneous utilization of sunlight for both photovoltaics (PV) and photosynthesis. A key challenge in agrivoltaic research involves identifying technologies applicable to a wide range of plant species and diverse geographic regions. To address this challenge, we adopt a multi-experimental and multi-species approach to assess the viability of semi-transparent, spectrally selective thin-film silicon PV technology. Our findings demonstrate compatibility with crop production in controlled environments for both plants and algae. Notably, selective thin-film PV exhibits the potential to enhance crop yields and serves as a photo-protectant. We observe that plant and algal growth increases beneath the selective PV film when supplemented with appropriate diffuse light in the growth environment. Conversely, in situations where light intensity exceeds optimal levels for plant growth, the selective PV film provides a photo-protective effect. These results suggest potential supplementary benefits of employing this technology in regions characterized by excessive light irradiation, where it can contribute to healthy plant growth.

Isotropic gap formation, localization, and waveguiding in mesoscale Yukawa-potential amorphous structures

Amorphous photonic structures are mesoscopic optical structures described by electrical permittivity distributions with underlying spatial randomness. They offer a unique platform for studying a broad set of electromagnetic phenomena, including transverse Anderson localization, enhanced wave transport, and suppressed diffusion in random media. Despite this, at a more practical level, there is insufficient work on both understanding the nature of optical transport and the conditions conducive to vector-wave localization in these planar structures, as well as their potential applications to photonic nanodevices. In this study, we fill this gap by investigating experimentally and theoretically the characteristics of optical transport in a class of amorphous photonic structures and by demonstrating their use to some basic waveguiding nanostructures. We demonstrate that these 2-D structures have unique isotropic and asymmetric band gaps for in-plane propagation, controlled from first principles by varying the scattering strength and whose properties are elucidated by establishing an analogy between photon and carrier transport in amorphous semiconductors. We further observe Urbach band tails in these random structures and uncover their relation to frequency- and disorder-dependent Anderson-like localized modes through the modified Ioffe-Regel criterion and their mean free path - localization length character. Finally, we illustrate that our amorphous structures can serve as a versatile platform in which photonic devices such as disorder-localized waveguides can be readily implemented.

Macroporous Directed and Interconnected Carbon Architectures Endow Amorphous Silicon Nanodots as Low-Strain and Fast-Charging Anode for Lithium-Ion Batteries

HighlightsMPCF@VG@SiNDs/C, constructed by uniformly dispersing amorphous Si nanodots in carbon nanospheres that are welded on the wall of the macroporous carbon frameworks by vertical graphene, is synthesized and has achieved a few kilogram production per batch.Finite element imitation reveals that amorphous Si nanodots with high dispersity in carbon nanosphere can achieve ultra-low stress and strain values during lithiation.Unique low-strain property and fast-charging capability are achieved under industrial electrode conditions.

Polarization-insensitive and polarization-controlled dual-band third-harmonic generation in silicon metasurfaces driven by quasi-bound states in the continuum

High-refractive-index nanostructures offer versatile opportunities for nonlinear optical effects, due to their ability to strongly confine field into a subwavelength scale. Herein, we propose a rhomboidal amorphous silicon metasurface to realize high-efficiency dual-band third-harmonic generation (THG), based on the supported dual quasi-bound states in the continuum (Q-BICs). Owing to the very large field confinement inside the metasurface empowered by Q-BICs, the THG efficiency up to 3.74 × 10−3 with the peak pump intensity of 30 MW/cm2 is observed. Meanwhile, thanks to the very high quality factor of Q-BICs, the ultra-narrow nonlinear process with the full width at half maximum less than 1 nm is also witnessed, suggesting the good monochromaticity. Interestingly, the dual-band THG is verified to be polarization-dependent and polarization-insensitive, respectively. The finite element method simulations exhibit that the polarization-dependent THG is attributed to the Q-BIC driven by the electric quadrupole characterized by a pair of anti-parallel electric dipoles along the x axis, which are only excited by the x-linearly polarized light. On the contrary, the polarization-insensitive THG is enabled by another Q-BIC governed by the magnetic dipole resonance with circular electric field vectors, which can be excited by any linearly polarized light. The polarization-controlled and polarization-independent dual-band THG enabled by the physics of Q-BICs would open possibilities for designing switchable nonlinear light sources. The proposed dual Q-BICs scheme undoubtedly can serve as a universal recipe for other nonlinear effects, including sum-frequency generation, difference-frequency generation, and high-order harmonics.

Cross-sectional profile of photocarrier mobility in thin-film solar cells via multimolecular recombination and charge extraction by linearly increasing voltage (cs-p-CELIV)

The ability to spatially resolve the carrier mobility profile along the cross section of micrometer-thin solar cells is vital, both for fundamental studies in photovoltaics and as quality control for reproducibly obtaining high conversion efficiencies in commercial solar cell modules. Presently, no technique capable of such an endeavor is available to the best of our knowledge. Here, we introduce a novel method capable of profiling the carrier mobility along the z axis in thin-film photovoltaics. Our setup is based on the integration of photogenerated charge extraction by linearly increasing voltage (p-CELIV) with a scanning confocal optical microscope (SCOM) toward a confocal and cross-sectional p-CELIV (cs-p-CELIV) system. As monomolecular recombination of excess carriers is the most frequent radiative pathway for electrons and holes in solar cells at low power density of illumination, while multimolecular recombination dominates at high power, enhanced multimolecular recombination occurs at the SCOM focal plane. Thus, the cs-p-CELIV signal provides enhanced information on the mobility of all of the cross-sectional layers except the focal plane. By scanning the focal plane along the z axis, the mobility profile can be derived. To demonstrate our technique, we use it to investigate the carrier mobility in three hydrogenated amorphous silicon (a-Si:H) solar cells. The mobility profiles obtained by cs-p-CELIV correlate well with well-known depletion layer effects and the H content profile in a-Si:H, which is measured independently. Our findings are in excellent agreement with models suggesting a critical role of Si–H bonding in locally determining the carrier mobility in a-Si:H.

Defects in poly-Silicon and amorphous Silicon solar cells

The paper introduces the issue of the typical defects present in PV-cell. Typical defects are introduced for two different technologies of photovoltaic devices: the multicrystal Silicon and the amorphous Silicon one. The defects have been implemented on a tridimensional model of a well operating cell implemented in Comsol Multiphysics environment. The aim of the paper is to simulate the behaviour of possible defect as they are pointed out by means of thermography. Defects have been modelled as they are described in literature and implemented into the model of photovoltaic cells. A multiphysical analysis, needed to study the effects of the defects on the cell behaviour, has been conducted using utilities available in Comsol environment.

History of the amorphous silicon on crystalline silicon heterojunction solar cell

Some commercially available solar panels with very high efficiencies for terrestrial photovoltaic applications are based on the amorphous silicon on crystalline silicon material system. This type of heterostructure has a more than 40 years old history. The early development of the technology and the results, obtained in the last years with this type of solar cell are reviewed. In particular it is demonstrated how the physical understanding of the interface properties and band-structure was important for the development of high efficiency solar cells.

Carrier mobility in organic semiconductors with an exponential density of states under the framework of admittance spectroscopy

The carrier transport in amorphous organic semiconductors with an exponential density of states is systematically studied under the framework of admittance spectroscopy. Due to the exponential distribution, the slope of the double logarithmic curve of current density versus voltage is expressed as b+2, where b relates to the width of the density of states. And the mobility is proportional to nb, where n is the density of carrier. In this case, the peak frequencies of the negative differential susceptance and imaginary part of impedance turn out to be functions of parameter b. Therefore, the relation between transit time and mobility will be a linear function of parameter b. Applying our model to interpret experimental data of both small molecular and polymeric materials are illustrated. The contributions of electric field and of carrier density to mobility are discussed.