Ultrathin Amorphous Silicon Research Articles

Influence of Photonics and Plasmonics Effect on Ultrathin Amorphous Silicon Thin Film Solar Cell

Abstract Our recent surge in silicon derived materials has major demand in thin film photovoltaic (PV) modules and enhancing the significant numbers. The rigorous coupled wave analysis method is a simple and fast method also known as developed to determine the light absorption and cell efficiency. The optics of thin film solar cells (amorphous silicon) garnering crucial role in the photovoltaic market. In this work, an ultrathin thin film amorphous silicon solar cell PV performance investigated by periodically textured surfaces at the nanoscale level. This analysis of periodic textured substrate was deriving optimal surface textures. The nanogratings lead to light scattering mechanism with the higher order diffraction angle and enhanced the light absorption of the incidence spectrum. The influence of grating period and height, the collection of the charge carriers increased at various wavelengths from ultraviolet, visible and infrared spectral regions are discussed with the assistance of photonic and plasmonic modes. Finally, nanoscale engineering mechanism the optimized thin film amorphous silicon solar cell yielded the highest current densities (22.6 and 23.8 mA/cm2) in both polarization modes.

Chronic Stability of Local Field Potentials Using Amorphous Silicon Carbide Microelectrode Arrays Implanted in the Rat Motor Cortex.

Implantable microelectrode arrays (MEAs) enable the recording of electrical activity of cortical neurons, allowing the development of brain-machine interfaces. However, MEAs show reduced recording capabilities under chronic conditions, prompting the development of novel MEAs that can improve long-term performance. Conventional planar, silicon-based devices and ultra-thin amorphous silicon carbide (a-SiC) MEAs were implanted in the motor cortex of female Sprague-Dawley rats, and weekly anesthetized recordings were made for 16 weeks after implantation. The spectral density and bandpower between 1 and 500 Hz of recordings were compared over the implantation period for both device types. Initially, the bandpower of the a-SiC devices and standard MEAs was comparable. However, the standard MEAs showed a consistent decline in both bandpower and power spectral density throughout the 16 weeks post-implantation, whereas the a-SiC MEAs showed substantially more stable performance. These differences in bandpower and spectral density between standard and a-SiC MEAs were statistically significant from week 6 post-implantation until the end of the study at 16 weeks. These results support the use of ultra-thin a-SiC MEAs to develop chronic, reliable brain-machine interfaces.

Ultrathin Film Amorphous Silicon Solar Cell Performance using Rigorous Coupled Wave Analysis Method

The issues related to global energy needs and environmental safeties as well as health crisis are some of the major challenges faced by the human, which make us to generate new pollution-free and sustainable energy sources. For that the optical functional nanostructures can be manipulated the confined light at the nanoscale level. These characteristics are emerging and leading candidate for the solar energy conversion. The combination of photonic (dielectric) and plasmonic (metallic) nanostructures are responsible for the development of better optical performance in solar cells. Here, the enhancement of light trapping within the thin active region is the primary goal. In this work, we have studied the influence of front-ITO (rectangular) and back-Ag (triangular) nanogratings were incorporated with ultrathin film amorphous silicon (a-Si) solar cell by using rigorous coupled wave analysis (RCWA) method. The improvement of light absorption, scattering (large angle), diffraction and field distributions (TE/TM) were demonstrated by the addition of single and dual nanogratings structures. Significantly, the plasmonic (noble metal) nanogratings are located at the bottom of the cell structure as a backside reflector which is helpful for the omni-directional reflection and increased the path length (life time) of the photons due to that the collection of the charge carriers were enhanced. Further, the proposed solar cell structure has optimized and compared to a back-Ag, front-ITO and dual nanogratings based ultrathin film amorphous silicon solar cell. Finally, the obtained results were evidenced for the assistance of photonic and plasmonic modes and achieved the highest current density (Jsc) of 23.82 mA/cm2(TE) and 22.75 mA/cm2 (TM) with in 50 nm thin active layers by integration of (dual) cell structures.

Performance improvement of an ultra-thin amorphous silicon solar cell using multilayers chirped diffraction back gratings

In this paper, a systematic design of a novel back reflector using chirped grating structures is investigated for thin-film amorphous silicon (a-Si) solar cells. At first, a cell with an optimum ITO antireflecting layer is simulated and a photocurrent of 17.67 mA cm−2 is obtained. Then a conventional grating from SiO2 is evaluated and the maximum photocurrent of 18.97 mA cm−2 is calculated. Then a thin-film solar cell based on the chirped back grating is designed and the photocurrent is increased to 19.30 mA cm−2. Also, their integrated optical absorption is compared for better understanding. To give a numerical comparison of the cells with a different number of chirped grating layers, a short circuit current for different numbers of grating layers is analyzed. It is shown that maximum current density is obtained for 5 layers grating with the chirped coefficient length of near 20 nm. It is believed that chirped back grating can be used to design higher performance thin film a-Si solar cells and the results are helpful for photovoltaic applications.

The role of photonic and plasmonic modes in ultrathin amorphous silicon solar cells using finite difference time domain method

In photovoltaic market, the enhancement of optical performance in an ultra-thin film amorphous silicon (a-Si) solar cell is significant. Our main objective is to design and simulate a highest current density by using various nanostructures integrated with ultrathin a-Si solar cells. In this proposed work, the various photonic and plasmonic nanostructures were used in front side of the absorber layer and enhanced the collection of charge carriers due to that an improved the current density in ultrathin a-Si solar cells. Using finite-difference time-domain (FDTD) method, the obtained results indicate the optimized SiO2 nanogratings and Si3N4 thin films acting as an anti-reflection coating (ARC) layer with air medium (AM1.5) which showed significant current density of 16.25 mA/cm2 in ultra-thin a-Si solar cells. Finally, the light trapping mechanism evidenced the importance of nanostructures using transverse electric (TE) and magnetic (TM) field distributions by changing the various incident wavelength.

Performance Assessment of Hetero-Junction Intrinsic Thin Film HIT Photovoltaic Module Using Machine Learning Methods

A solar cell built of ultra-thin amorphous silicon and high-quality mono-crystalline silicon is known as a hetero-junction intrinsic thin film. It has a pyramid surface on the front that increases sunlight absorption. The operating environment has a significant impact on the performance of hetero-junction intrinsic thin-film photovoltaic modules with real I–V (current-voltage) characteristics. Changes in the environment have a significant impact on solar irradiation. Clouds also have a significant impact on the solar irradiation that a PV cell receives. In this project, we will use the Random Forest Regression machine learning algorithm to investigate the effects of sudden changes in environmental conditions on power output and module temperature of an HIT (Heterojunction with Intrinsic Thin Layer) module, where irradiance, temperature, and module efficiency parameters are taken into account when designing modules. The algorithm’s output will be studied to gain a better understanding of performance variations as well as the behavior of the power output and module temperature when subjected to random influences induced by various environmental variables. The suggested algorithm is not restricted to a certain module technology or geographic location.

Study of ultrathin‐film amorphous silicon solar cell performance using photonic and plasmonic nanostructure

The photonic and plasmonic nanostructures are highly feasible for enhanced light trapping mechanisms. These nanostructures hold great promises for better photovoltaic performance by yielding the highest light-harvesting photons within the few nanometer absorber regions. The shed light on the nano-scaled structures (thin films and nanogratings) is responsible for the highest scattering mechanism with the omnidirectional diffraction angles and enhanced life time of the photons. In this research work, we have focused on improved ultrathin film amorphous silicon (a-Si) solar cell performance, which was integrated by top-SiO2 and bottom-Ag nanogratings as a backside reflector by using rigorous coupled-wave analysis method. The SiO2 antireflection coating, nanogratings, and absorber (a-Si) layer thicknesses were optimized for better photovoltaic performance. With the influence of optimization parameters, the highest current density of 27.03 and 33.53 mA/cm2 were obtained from transverse electric and transverse magnetic polarization conditions due to the surface guided-mode, Fabry–Perot resonance, surface excitation, localized fields, and surface plasmon polariton modes.

Electronic energy loss and straggling in low energy H+ and H2 + interaction with silicon films

ABSTRACT The appearance of atomic structures of nanoscopic dimensions, with new and interesting physical properties, requires revisiting various aspects of particle interaction with solid matter. For this purpose in this work we present a study of electronic energy loss of H+ and protons (fragments) from the dissociation of H2 + ions interacting with ultra-thin amorphous silicon films for incident beam energies from 1 to 10 keV/u. We report measurements of energy distributions of transmitted protons and molecular fragments through these films, from which we derive the average energy losses and the energy loss straggling. Our experimental findings turn out to be in good agreement with nonlinear electronic stopping power models and some previous experimental data.

Implementation of full-area-deposited electron-selective TiOx layers into silicon solar cells

We examine two different silicon solar cell designs featuring full-area electron-selective contacts based on ultrathin (2–3 nm) titanium oxide (TiOx) films deposited by atomic layer deposition. The first cell design applies a layer stack to the cell front, which is composed of an ultrathin intrinsic amorphous silicon (i-a-Si:H) layer for interface passivation, the TiOx film and an indium tin oxide (ITO) layer to provide a good lateral conductance for electrons to the metal fingers. Whereas carrier lifetime measurements on test structures promise high implied open-circuit voltages Voc up to 726 mV, the realized solar cells achieve disappointingly low Voc values <400 mV. The J-V parameters of this cell type are negatively affected by a reverse diode occurring due to the contacting of the TiOx by the high-work function ITO layer. In the second cell type, we implement a layer stack to the cell rear, which is composed of an ultrathin silicon oxide (SiOy) layer, the TiOx film and a full-area-deposited aluminum (Al) layer. Initial Voc values of these cells are relatively low (<600 mV), but improve significantly after annealing at 350°C. The best cell featuring a SiOy/TiOx/Al rear contact achieves an open-circuit voltage of 661 mV and an efficiency of 20.3%. No reverse diode is observed, which is attributed to the lower work function of the Al compared to ITO in the first cell design. From internal quantum efficiency measurements, we extract a rear surface recombination velocity Srear of (52±20) cm/s for our best cell, which is well compatible with efficiencies exceeding 23%.

Enhanced coupling of broadband light into amorphous silicon via periodic nanoplasmonic arrays**DISTRIBUTION STATEMENT A. Approved for public release: distribution unlimited. This material is based upon work supported by the Department of the Army under Air Force Contract No. FA8721-05-C-0002 and/or FA8702-15-D-0001. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily

Achieving enhanced coupling of solar radiation over the full range of the silicon absorption spectrum up to the bandgap is essential for increased efficiency of solar cells, especially thin film versions. While many designs for enhancing trapping of radiation have been explored, detailed measurements of light scattering inside silicon cells is still lacking. Here, we demonstrate experimentally and computationally that plasmonic-assisted localized and traveling modes can efficiently couple red and infrared radiation into ultrathin amorphous silicon (a-Si) layers. Utilizing patterned periodic arrays of aluminum nanostructures on thin a-Si, we perform specular and diffuse reflectivity and transmission measurements over a broad spectrum. Based on these results, we are able to separate parasitic absorption in aluminum plasmonic arrays from enhanced light absorption in the 200 nm thick amorphous silicon layer, as compared to a blank silicon layer. We discover a very efficient near-infrared a-Si absorption mechanism that occurs at the transition from the radiative to evanescent diffractive coupling, analogous to earlier surface-enhanced infrared studies. These results represent a direct demonstration of enhanced radiation coupling into silicon due to large angle scattering and show a path forward to improved ultrathin solar cell efficiency.

Improving the Efficiency of Thin Film Amorphous Silicon Solar Cell by Changing the Location and Material of Plasmonic Metallic Nanostructures

In this work we present a 3D-finite difference time domain (FDTD) simulation of ultra thin amorphous silicon solar cell. The optical generation rate and plasmonic resonance enhance absorption in thin film cell in which silver nanoparticles are imbedded inside the depletion region of p-n junction. Here, the operation of thin film solar cell has been analyzed. Here, by inserting the metal nanoparticles within the active layer in the depletion region of the p-n junction, a new structure has been introduced. We have utilized three different materials, gold, silver and aluminium and the efficiencies of 5.27%, 5.3% and 3.74% have been obtained respectively. The results indicate a significant increase in the efficiency of proposed solar cell with silver nanoparticles.

Funneling and guiding effects in ultrathin aSi-H solar cells using one-dimensional dielectric subwavelength gratings

Ultrathin amorphous silicon hydrogenated (aSi-H) solar cells grown on a one-dimensional (1-D) dielectric subwavelength gratings improve the short circuit current by a factor of more than 51% when compared with conventional, flat ultrathin aSi-H devices. This improvement is possible due to several mechanisms. In addition the increase in exposed area caused by the nanostructured surface, a reliable computational electromagnetic evaluation of the interaction of the solar spectrum with the cell structure demonstrates that absorption at the active layer is enhanced and also reflectivity is decreased. In addition, the absorbed power at the nonactive layers is larger, helping to increase the temperature and mitigate the Staebler–Wronski effect. The detailed analysis of the power flux inside the structure has also shown that funneling and guiding mechanism are at play, increasing the optical path within the active layer that produces a better performance of the cell.

Extraordinary Figure‐of‐Merit of Magnetic Resonance from Ultrathin Silicon Nanohole Membrane as All‐Dielectric Metamaterial

Metamaterial allows novel nanophotonic applications such as negative permeability, negative refractive index, and near‐zero index. In particular, all‐dielectric metamaterials recently create new opportunities for manipulating electromagnetic fields, taking full advantage of low‐loss, bandwidth enhancement, and isotropic responses. Here a silicon dielectric metamaterial is reported in near‐infrared region, exhibiting extraordinarily figure‐of‐merit, defined by sensitivity (resonance shift/refractive index change) over full width at half maximum, from magnetic resonance shift depending on index changes of surrounding medium. This silicon dielectric metamaterial comprises subwavelength nanohole arrays in a square lattice on an ultrathin amorphous silicon membrane. The ultrathin silicon nanohole membrane is fabricated on a glass wafer by using e‐beam lithography, silicon reactive ion etching, and hydrogen fluoride wet etching. This all‐dielectric metamaterial successfully demonstrates exceptional figure‐of‐merit of 29, which is 7.6 times higher than those values of conventional metamaterials. This novel metamaterial enables not only the label‐free detection of chemical and biological molecules with different mass concentrations but also the in situ reaction monitoring of biochemical molecules.

Colloidal transfer printing method for periodically textured thin films in flexible media with greatly enhanced solar energy harvesting

The successful fabrication of high-performance flexible thin film solar cells (TFSCs) directly on diverse substrates is intrinsically limited by the processing temperature and substrate property. In this work, a colloidal transfer-printing (CTP) method is developed to fabricate large-area flexible thin-film absorbers with an antireflection coating and periodic configurations. Compared with a planar film, such structures exhibit much lower reflectance due to the antireflection introduced by the textured polydimethylsiloxane and the enhanced scattering introduced by the periodic back-scattering reflector. Optical simulation using the finite-element method indicates the structural periodicity for maximum light absorption is of 300 nm for an ultrathin amorphous silicon (a-Si) film with a thickness of 160 nm. The patterned a-Si film yields an overall absorption of 64.8%, which is much larger than the planar counterpart of 38.5%. This new approach to thin-film transfer can be readily extended to other material systems and device structures, opening up an effective alternative to traditional fabrication of the low-cost and high-performance optoelectronic devices.

Directed dewetting of amorphous silicon film by a donut-shaped laser pulse

Irradiation of a thin film with a beam-shaped laser is proposed to achieve site-selectively controlled dewetting of the film into nanoscale structures. As a proof of concept, the laser-directed dewetting of an amorphous silicon thin film on a glass substrate is demonstrated using a donut-shaped laser beam. Upon irradiation of a single laser pulse, the silicon film melts and dewets on the substrate surface. The irradiation with the donut beam induces an unconventional lateral temperature profile in the film, leading to thermocapillary-induced transport of the molten silicon to the center of the beam spot. Upon solidification, the ultrathin amorphous silicon film is transformed to a crystalline silicon nanodome of increased height. This morphological change enables further dimensional reduction of the nanodome as well as removal of the surrounding film material by isotropic silicon etching. These results suggest that laser-based dewetting of thin films can be an effective way for scalable manufacturing of patterned nanostructures.

Plasmonic effects in ultrathin amorphous silicon solar cells: performance improvements with Ag nanoparticles on the front, the back, and both.

Thin-film hydrogenated amorphous silicon (a-Si:H) solar cells that are free-standing over a 2x2 mm area have been fabricated with thicknesses of 150 nm, 100 nm, and 60 nm. Silver nanoparticles (NPs) created on the front and/or back surfaces of the solar cells led to improvement in performance measures such as current density, overall efficiency, and external quantum efficiency. The effect of changing silver nanoparticle size and incident light angle was tested. Finite-Difference Time-Domain simulations are presented as a way to understand the experimental results as well as guide future research efforts.

Neutron Reflectometry to Measure In Situ Li Permeation through Ultrathin Silicon Layers and Interfaces

High-intensity specular neutron reflectometry was used to measure atomic transport processes in the solid state in-situ. As a model system, Li transport through ultrathin amorphous silicon layers (5 nm) and adjacent lithium silicate interfaces relevant for battery applications is studied. For the experiments a multilayer structure consisting of five [Si/natLiNbO3/Si/6LiNbO3] units was investigated, which was produced by ion beam sputtering. LiNbO3 is solely used as a tracer reservoir. Thin lithium silicate layers are formed at Si/LiNbO3 interfaces during sputtering. Two types of Bragg peaks are detectable in the neutron reflectivity pattern. One originates from the double layer periodicity introduced by the LiNbO3/Si chemical contrast, the other from the four-layer periodicity introduced by the Li isotope contrast of the natLiNbO3 and 6LiNbO3 layers. If the multilayer arrangement is annealed at 240°C, Li diffusion through the silicon layer between the two isotope reservoirs is induced and only the Bragg peak due to Li isotope contrast variation is reduced, while the peak due to chemical contrast variation remains constant. High-intensity specular neutron reflectometry allows to record reflectivity patterns within some minutes, which is the base for continuous in-situ measurements during annealing. Simulation tools allow to derive the Li permeability (diffusivity x solubility) in silicon.

Ultrathin amorphous silicon thin-film solar cells by magnetic plasmonic metamaterial absorbers

Energy harvesting in metamaterial-based solar cells containing an ultrathin α-Si film sandwiched between a silver (Ag) substrate and a square array of Ag nanodisks and combined with an indium tin oxide (ITO) anti-reflection layer is investigated.

Optical Simulation of Periodic Surface Texturing on Ultrathin Amorphous Silicon Solar Cells

In this paper, we study the effect of sinusoidal textures on light absorption properties in an ultrathin amorphous silicon (a-Si) solar cell with conductive transparent layer composed of dielectric/metal/dielectric layers by using 2-D optical simulation. We found that the absorption at visible region can be enhanced at an optimized period (P) and height (H) combination, despite the weakening of a cavity resonance at the a-Si layer. The short- circuit current density for the structure with P = 300 nm and H = 180 nm showed a 52% higher value than that of the reference. A random texture was also simulated, and the absorption spectrum of the a-Si layer was reproduced by superposition of those with sinusoidal textures weighted by power spectrum density of the random texture, which implies the superiority of sinusoidal texture over random texture.

Colored ultrathin hybrid photovoltaics with high quantum efficiency

Most current solar panels are fabricated via complex processes using expensive semiconductor materials, and they are rigid and heavy with a dull, black appearance. As a result of their non-aesthetic appearance and weight, they are primarily installed on rooftops to minimize their negative impact on building appearance. The large surfaces and interiors of modern buildings are not efficiently utilized for potential electric power generation. Here, we introduce dual-function solar cells based on ultrathin dopant-free amorphous silicon embedded in an optical cavity that not only efficiently extract the photogenerated carriers but also display distinctive colors with the desired angle-insensitive appearances. Light-energy-harvesting colored signage is demonstrated. Furthermore, a cascaded photovoltaics scheme based on tunable spectrum splitting can be employed to increase power efficiency by absorbing a broader band of light energy. This study pioneers a new approach to architecturally compatible and decorative thin-film photovoltaics. Ultrathin solar cells that can also act as coloured signs and displays have been developed by scientists in the USA. Kyu-Tae Lee and co-workers from the University of Michigan fabricated them by embedding a very thin (10–30 nm) layer of amorphous silicon within a metal–semiconductor–metal optical cavity. The cavity acts as a Fabry–Perot resonator that reflects a particular colour; importantly, it is insensitive to the polarization state or angle (up to 60°) of the incident light. By combining cells of different thickness (and hence different colours), arbitrary patterns or images can be created. The design has yielded solar cells with power conversion efficiencies of around 3%, despite using an amorphous silicon layer that is ten times thinner than those usually found in solar cells.