Electron-hole Pair Generation Rate Research Articles

(Invited) MoS2 Photodetectors for Near-Infrared Biosensing Applications

Device researchers have been actively developing novel diagnostic biosensors using metallic nanoparticle-based plasmonic immunoassays.[1] In these biosensing devices, photodetectors with high photoresponsivity and low internal noise levels are integrated to detect the marginal optical signals change induced by biomarker binding events (i.e., Antigen-antibody binding). Recently, atomically thin layers of molybdenum disulfide (MoS2) have been integrated with plasmonic components to enable fast and sensitive colorimetric monitoring of disease-related biomarkers.[2] However, such biosensors are mostly operated in the ultraviolet/visible range, which needs a purification step to separate out a variety of unwanted biomaterials that absorb visible light and takes several hours of preparation steps. Thus, it would be amenable to develop biosensors for biomolecular detections or immunoassays in the whole blood (WB) analytes without any sample preparations.[3] To address the issues mentioned above, recent studies have demonstrated the engineered gold nanoparticles (AuNPs) that have localized surface plasmonic resonance (LSPR) shift around near-infrared (NIR) wavelength region. However, a high-sensitivity photodetector under NIR region is still required to detect marginal signal changes due to the target biomarker binding events. Meanwhile, the MoS2 material has been reported to exhibits superior photo-response characteristics.[4] MoS2 is a transition metal dichalcogenide material of which single- and multi-layer films exhibit an efficient electron-hole pair generation rate under photoexcitation and therefore high photo absorption as compared to silicon. Therefore, a systematical study on MoS2 photoconductors to optimize the optoelectronic properties under near-infrared (NIR) (λ = 650 nm) operation can enable zero-preparation WB immunoassays combined with specially engineered AuNPs.In this work, we study the photo-response properties (i.e., Photoresponsivity spectrum) of in-plane MoS2 photodetectors as the function of their geometric dimensions and fabrication conditions. Recent study shows that an annealing temperature after exfoliation can etch the upper layers of MoS2 flakes and clean stains on the device and therefore improve device performances (e.g., mobility). [5] This work enables the NIR operation capabilities of plasmonic colorimetric biosensing by introducing the optimized MoS2 photodetector fabrication practice. This approach reduces assay preparation times and mitigate background interference even with WB analytes and thereby enable the WB point-of-care immunoassays.

Optimum Solar Cell Power Conversion Efficiency-Based Patterned Planar Solar Surface Morphology with Various Solar Cell Absorber Structures

This paper simulated the optimum solar cell power conversion efficiency-based planar solar surface morphology with various solar cell absorber structures. The spectral light intensity, reflected, absorbed, and transmission coefficients versus wavelength band spectrum varied from 300[Formula: see text]nm to 1300[Formula: see text]nm through the visible to near-infrared regions. The optimum solar cell performance parameters or key parameters are studied with different solar cell structure designs based on different surface contact and back contact layers. Cumulative generation current, cumulative electron–hole pair generation rate and electron–hole pair generation rate are clarified versus substrate depth for various solar cell structure designs. The absorbed current in substrate is optimized for various solar cell structure designs. Maximum power voltage and current are also optimized for the proposed solar cell structure design. The effective solar cell power efficiency is also demonstrated based on the optimized maximum power current and maximum power voltage.

The organic HTL in highly efficient germanium-alloyed CsSnI3 perovskite solar cell: a modelling and computational analysis

It is usually anticipated that perovskites will be an appealing material for extremely effective solar cells. However, its practical applications are constrained by its hazardous properties and stability. Thus, CsSn0.5Ge0.5I3, a more environmentally benign substitute for toxic lead-based perovskites, provides superior stability in solar cells. This work reports on the numerical modeling and computational analysis of a heterostructure CsSn0.5Ge0.5I3, with TiO2 and D-PBTTT-14 serving as the electron and hole transport layers, respectively. The introduction of D-PBTTT-14 as a hole transport layer was motivated by its superior stability over existing organic HTLs. Furthermore, the higher electron–hole pair generation rate and very favorable absorption coefficients of each layers manifested improved efficiency. Various parameters were examined to enhance the newly designed solar cell performance such as: thickness, defect density, doping density, coefficient of radiative recombination, defect at interface, shunt and series resistance, front and back contacts, and operating temperature. Perovskite solar cells with their current architecture have the potential to achieve a current density (Jsc) of 28.31 mA cm−2, an open-circuit voltage (Voc) of 1.24 V, a fill factor (FF) of 85.90%, and efficiency of 30.27%.

Three-dimensional numerical simulation of single event upset effect based on 55 nm DICE latch unit

With the development of nanoscale circuit technology, the on-track error rate of digital circuit and the effect of single event upset have become more pronounced. The radiation resistance research on DICE SRAM or DICE flip-flop device has been carried out extensively, including 65 nm, 90 nm, and 130 nm. However, the research on 55 nm DICE latch has not been reported. Using a three-dimensional device model of the 55 nm bulk silicon process established by the simulation tool TCAD, we verify the reinforcement performance of the DICE circuit, and clarify the effects of different incident conditions on DICE circuits. At the same time, we carry out a comparison of anti-SEU performance between NMOS transistor and PMOS transistor in the 55 nm process through comparative simulation experiments and quantitative analysis. The result shows that one of the important factors is the LET value which affects the generation rate of electron-hole pairs. A higher LET value will extend the upset recovery time of device and increase the peak of voltage. In addition, the difference in charge-sharing mechanism between transistors leads to the recovery time of PMOS higher than that of NMOS. As the angle of incidence increases, the charge-sharing mechanism between adjacent devices is enhanced, and electron-hole pairs ionized in sensitive regions increase. Due to the difference in charge mobility, the sensitivity of the angle of incidence of Nhit in DICE is much greater than that of Phit. Therefore, strict tilt angle incident test evaluation is required for DICE device before practical application. Finally, the large distance between adjacent MOS tubes will weaken the charge-sharing mechanism and reduce the charge collection of adjacent MOS tubes. Simulation result shows that the distance between the MOS transistors in the 55 nm process cannot be less than 1.2 μm. The relevant simulation results can provide a theoretical basis and data for supporting the study of the physical mechanism of SEU and reinforcement technology, thereby promoting the application of memory devices to the aerospace field.

Laser Voltage Probing Attack Detection With 100% Area/Time Coverage at Above/Below the Bandgap Wavelength and Fully-Automated Design

In this work, a detection scheme signaling the occurrence of laser voltage probing (LVP) attacks in digital designs (e.g., cryptographic circuits) is introduced. The scheme comprises a standard cell-based photosensor fabric and distributed detectors. By construction, the scheme conforms the standard cell design discipline, restricted layout design rules, and commercial place and route tools. This allows seamless integration with automated design flows, and immediate adoption in a design-agnostic fashion. Hundred percentage time and area coverage is achieved for full protection against LVP attacks, while not requiring any calibration. Extensive attacks with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $</tex-math> </inline-formula> 150 h of characterization with a state-of-the-art LVP equipment on a 28-nm testchip demonstrate laser detection at both above-and below-bandgap wavelengths and, hence, even at the very low electron-hole pair generation rate of the former ones. Attacks to an advanced encryption standard (AES) core are shown to be flagged at any practical laser intensity and best-in-class true 220-nm laser spot. Low circuit activity confines its power to leakage, amounting to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 0.1% of the AES power. At the worst case, 150% area overhead is substantially lower in practical cases where the information-sensitive blocks are a portion of it (e.g., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 20% in an advanced reduced instruction set computer machines (ARM) Cortex-M4 processor with a secure AES accelerator). To the best of the authors’ knowledge, this is the first demonstration of a design-agnostic on-chip protection against LVP attacks with full-area coverage under unmodified manufacturing/packaging process.

Rational Synthesis of Au-CdS Composite Photocatalysts for Broad-Spectrum Photocatalytic Hydrogen Evolution.

Incorporation of plasmonic metal nanomaterials can significantly enhance the visible light response of semiconductor photocatalysts via localized surface plasmon resonance (LSPR) mechanisms. However, the surfaces of plasmonic metal nanomaterials are often covered with surfactant molecules, which is undesired when the nanomaterials are used for photocatalytic hydrogen evolution, since surfactant molecules could significantly compromise the nanomaterials' cocatalyst functionalities by blocking the active sites and/or by inhibiting the surface charge transfer process. Herein, we demonstrate a method that assembles Au nanoparticles (NPs) into Au colloidosomes (AuCSs) without modifying their surfaces with surfactants. The resulting AuCSs were then coupled with CdS for the formation of Au-CdS composite photocatalysts through an in situ deposition method. The assembly of Au NPs induced a broader and stronger LSPR response for AuCSs, while the absence of surfactants allowed them to act efficiently as cocatalysts. This essentially enhanced the electron-hole pair generation rate and further their utilization efficiency, leading to an extremely high hydrogen evolution rate of 235.8 mmol·g-1·h-1 under simulated sunlight excitation.

Investigation of carrier transport and collection characteristics for GaAs-based betavoltaic batteries

This paper presents a simulation model to predict the performance of GaAs-based betavoltaic batteries with a p–n junction structure, in which the carrier transport and collection characteristics were studied. First, the electron–hole pair generation rate in the GaAs material under the irradiation of a 63Ni source was calculated using the Monte Carlo codes. Furthermore, by simulating the energy band structure, electric field distribution, and current density distribution in batteries with the finite element analysis software COMSOL Multiphysics, we analyzed the effects of structure parameters on the output performance. Our simulation results showed that the short-circuit current density (Jsc), open-circuit voltage (Voc), maximum output power density (Pm), and energy conversion efficiency (η) of the batteries are significantly affected by the thicknesses and doping concentrations of the p-region and n-region (Hp-GaAs, Hn-GaAs, Na, and Nd). The optimized GaAs-based battery with an Hp-GaAs value of 0.1 μm, an Hn-GaAs value of 9.9 μm, an Na value of 3.98 × 1016 cm−3, and an Nd value of 1 × 1015 cm−3 can achieve a Pm value of 0.080 μW/cm2. The related Jsc, Voc, and η values are 0.234 μA/cm2, 0.49 V, and 1.55%, respectively. When the top and bottom heavily doped layers are introduced, the Pm value of the battery is enhanced by 7.5% compared to that of the battery without heavily doped layers due to the formed drift fields.

Bismuth vanadate/MXene (BiVO4/Ti3C2) heterojunction composite: enhanced interfacial control charge transfer for highly efficient visible light photocatalytic activity.

We have synthesized BiVO4/Ti3C2 nanocomposite via a low-cost hydrothermal method and investigate its photocatalytic degradation activity against monoazo (methyl orange) and diazo dye (Congo red) in an aqueous solution under visible light. The physiochemical characterization exhibited that the addition of MXene in pristine BiVO4 nanocomposite led to an increase in specific surface area and reduction in optical band gap energy. MXene also helps in enhancing visible light response via a higher electron-hole pair generation rate and long lifetime. The synthesized BiVO4/Ti3C2 heterojunction composite exhibited 99.5 % degradation efficiency within 60 min for Congo red and 99.1 % for methyl orange solution in 130 min owed to a large specific surface area (1.79 m2/g), reduced band gap (1.99 eV), and low recombination rate of charge carriers. The chemical mechanism for BiVO4/Ti3C2 nanocomposite proposes that Ti3C2 role-plays as electron capture because of the higher potential of MXenes, tuning band gap energy which paves the way to excellent photocatalytic action. This work opens a new basis for developing Ti3C2 based promising and inexpensive co-catalyst for efficient solar utilization in photocatalytic-related applications in the future.

Influence of a 3D electric field enhancement model on the Monte Carlo calculation of the dark current in pixel arrays

A new three-dimensional (3D) electric field enhanced generation model has been developed to describe the electric field effects on the thermal electron–hole pair generation rate. The originality of this model lies in the full three-dimensional description of the synergetic mechanism between the Poole–Frenkel barrier lowering and the phonon-assisted tunneling mechanism. To do this, a classical one-dimensional (1D) model has been integrated over all possible directions of emission of the carriers. The 3D model has been implemented in a Monte Carlo tool devoted to the simulation of the dark current increase induced by radiations in image sensors. Our three-dimensional simulation has been compared to one-dimensional electric field effects’ simulations and experimental data found in the literature in the context of gold contamination. The consequence of using a three-dimensional electric field enhanced generation (EFEG) model is the reduction of the dispersive effect on the dark current distribution of the electric field; hence, each dark current peak is narrower and shows a higher peak's amplitude. The three-dimensional model needs to slightly change the cross-sectional parameters used for a 1D EFEG case to keep a realistic description of each dark current peak of the histogram. In the rest of the paper, we extended our work on constraints relative to space applications. The histograms of the simulated dark current taking into account one- and three-dimensional electric field enhancement effects have been estimated and compared to experimental data acquired after a proton irradiation at room temperature. The use of a three-dimensional model tends to give a more realistic prediction of the dark current non-uniformity in an irradiated pixel array.

Design and optimization of nanowire betavoltaic generators

A model used to simulate and optimize the performance of nanowire-based betavoltaic generators is developed. The optimum nanowire array geometry is established for devices made of silicon, gallium arsenide, and gallium phosphide for both nickel-63 and tritium sources by computing the energy capture efficiency for each case. The captured power for nanowire devices is shown to be drastically greater compared to planar betavoltaic generators with maximum improvement factors of approximately 7, 3, 5, and 9 for devices utilizing radioisotope sources of nickel-63, nickel citrate, tritium, and tritiated butyl, respectively. In addition, nanowire devices do not suffer from self-shielding effects, a large limitation in conventional, planar betavoltaics. By coupling the spatial distribution of electron–hole pair generation rate calculated from Monte Carlo simulations and a semiconductor charge-transport model, the diode design is optimized for the maximum power output. The top performing devices, utilizing a tritium source, exhibited an output power of approximately 4, 6, and 2 μW cm−2 for silicon, gallium arsenide, and gallium phosphide, respectively. Overall device efficiencies were found to range from 4% to 10%, surpassing several betavoltaic devices reported in the literature. It was also found that, contrary to the traditional betavoltaic design, semiconductors with higher bandgaps do not necessarily result in the best device performance due to additional material parameters, such as surface recombination velocity. Potential improvements for nanowire-based betavoltaic generators are suggested for additional investigation.

Effects of Incoherent Front Cover Glass on Current-Voltage Characteristics of Cu(In,Ga)Se2 Solar Cells: Investigation into Calculation Accuracy for Cover Glass Modeled as Optically Coherent or Incoherent

We numerically investigate the effects of an incoherent front cover glass on the current–voltage (J–V) characteristics of a Cu(In,Ga)Se2 (CIGS) solar cell using an integrated optoelectronic model. A 3-mm cover glass—the thickness of which was larger than the coherence length of sunlight—was incoherently modeled based on the equispaced thickness averaging method, where coherent simulation results of the wave equation were averaged over a set of equispaced phase thicknesses. The changes in optical power dissipation, absorptivity and electron–hole pair generation rate were calculated depending on the variation of the equispaced phase thickness. The calculation results of the J–V curves were obtained through numerical solutions of the coupled Poisson and continuity equations. By comparing the J–V curves calculated between coherently and incoherently modeled cover glass, we obtained a maximum ±0.54% deviation of the short-circuit current density. This demonstrates that the front cover glass should be modeled as optically incoherent to improve the calculation accuracy of the electrical J–V curves as well as the optical absorption characteristics in the optoelectronic modeling of CIGS solar cells.

La- and Mn-Codoped Bismuth Ferrite/Ti3C2 MXene Composites for Efficient Photocatalytic Degradation of Congo Red Dye.

Over the years, scarcity of fresh potable water has increased the demand for clean water. Meanwhile, with the advent of nanotechnology, the use of nanomaterials for photocatalytic degradation of pollutants in wastewaters has increased. Herein, a new type of nanohybrids of La- and Mn-codoped bismuth ferrite (BFO) nanoparticles embedded into transition-metal carbide sheets (MXene–Ti3C2) were prepared by a low-cost double-solvent sol–gel method and investigated for their catalytic activity in dark and photoinduced conditions. The photoluminescence results showed that pure BFO has the highest electron hole recombination rate as compared to all the codoped BFO/Ti3C2 nanohybrids. The higher electron–hole pair generation rate of the nanohybrids provides a suitable environment for fast degradation of organic dye molecules. The band gap of the prepared nanohybrid was tuned to 1.73 eV. Moreover, the BLFO/Ti3C2 and BLFMO-5/Ti3C2 degraded 92 and 93% of the organic pollutant, respectively, from water in dark and remaining in the light spectrum. Therefore, these synthesized nanohybrids could be a promising candidate for catalytic and photocatalytic applications in future.

Optical study on intrinsic exciton states in high-quality CH3NH3PbBr3 single crystals

Organolead halide perovskites have emerged as potential building blocks for photovoltaic and optoelectronic devices. Yet the underlying fundamental physics is not well understood. There is lack of agreement on the electronic band structures and binding energies of coupled electron-hole pairs (excitons), which drive the photophysical processes. In this work, we conducted temperature-dependent reflectance and photoluminescence experiments on high-quality ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbBr}}_{3}$ single crystals. Two direct optical transitions corresponding to intrinsic free-excitons are clearly resolved, showing excellent consistence between the low-temperature ($T=10$ K) reflectance and photoluminescence spectra. Remarkably, the excitons have different binding energies and behave oppositely with temperature, suggesting distinctive origins. Moreover, the asymmetric photoluminescence profile is counterintuitively dominated by the high-energy exciton that is explained by a long relaxation time between levels and by the favorable generation rate of electron-hole pairs at the high-energy band. Our study opens access to the intrinsic properties of ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbBr}}_{3}$ and sheds light to reconcile the large range of binding energies reported on these emergent direct band-gap semiconductors.

Synthesis of Spherical Carbon Nitride-Based Polymer Composites by Continuous Aerosol-Photopolymerization with Efficient Light Harvesting.

Here we report a novel, facile, and sustainable approach for the preparation of spherical submicrometer carbon nitride-based polymer composites by a continuous aerosol-photopolymerization process. In this regard, spherical mesoporous carbon nitride (SMCN) nanoparticles were initially prepared via a nanocasting approach using spray-drying synthesized spherical mesoporous silica (SMS) nanoparticles as hard templates. In addition to experimental characterization, the effect of porosity on the light absorption enhancement and consequently the generation rate of electron-hole pairs inside the SMCN was simulated using a three-dimensional finite difference time-domain (FDTD) method. To produce the carbon nitride-based polymer composite, SMCN nanoparticles exhibit excellent performance in photopolymerization of butyl acrylate (PBuA) monomer in the presence of n-methyldiethanolamine (MDEA) as a co-initiator in a continuous aerosol-based process. In this one-pot synthesis, SMCN nanoparticles act not only as photoinitiators but at the same time as fillers and templates. The average aerosol residence time in the photoreactor is about 90 s. The presented aerosol-photopolymerization process avoids the need for solvent and surfactant, operates at room temperature, and, more importantly, is suitable to produce the spherical composite with hydrophobic polymers. Furthermore, we simulated the condition of SMCN nanoparticles during illumination in the gas phase process, which can freely rotate. The results demonstrated that the hole (h(+)) density is almost equally distributed in the whole part of the SMCN nanoparticles due to their rotation, leading to efficient light harvesting and more homogeneous photoreaction. The combination of the outstanding features of environmentally friendly SMCN, photopolymerization, and aerosol processing might open new avenues, especially in green chemistry, to produce novel polymer composites with multifunctional properties.

Quantitative modeling of betavoltaic microbattery performance

This paper presents a simulation model to predict the power generation of p–n junction-based betavoltaic devices. The model provides two key aspects of information for device evaluation: electron–hole pair generation rate and device power output. A Monte-Carlo model was used to simulate generation rate and the device performance was simulated using the generation rate with Synopsys® Medici. We investigated the effects of the temperature, semiconductor materials with different bandgap energies (Si, Ge and SiC) and different isotope sources (Ni-63 and tritium) on the performance of betavoltaic microbatteries. Our simulation results indicate that a homojunction structure with wide bandgap semiconductor is more favorable for betavoltaic device performance. A simple wide bandgap p–n junction cell with an embedded radioisotope source could be the most promising candidate for betavoltaic applications.

Mechanisms of charge carriers nonequilibrium in transport processes in bipolar semiconductors

The interplay between physical origins of the nonequilibrium and their influence on the linear steady state transport processes in bipolar semiconductors are under investigation. Particular attention is paid to the influence of the energy nonequilibrium on the generation-recombination processes under various conditions. It is shown that in the case of the same (even if coordinate-dependant) temperature of the charge carriers and the phonons the volume recombination rate of the charge carriers in the steady state is completely determined by the splitting of the quasi-Fermi levels.Particular emphasis has been placed on the manifestation of the energy nonequilibrium in the presence of hot charge carriers in a semiconductor. It is shown that in this case the generation-recombination balance shifts, being completely equivalent to the appearance of an additional external generation of electron-hole pairs. The two-temperature model (with electron temperature being different from the single temperature of holes and phonons) of the Dember photovoltaic effect is used to illustrate that the electromotive force (emf) may differ significantly from its corresponding values with no hot electrons. This additional contribution to the emf does not depend neither on the Seebeck coefficient nor on the temperature gradient and the electron-hole pair generation rate. This contribution to the emf is exclusively determined by the magnitude of the electron heating.

Electron beam induced current in the high injection regime

Electron beam induced current (EBIC) is a powerful technique which measures the charge collection efficiency of photovoltaics with sub-micron spatial resolution. The exciting electron beam results in a high generation rate density of electron–hole pairs, which may drive the system into nonlinear regimes. An analytic model is presented which describes the EBIC response when the total electron–hole pair generation rate exceeds the rate at which carriers are extracted by the photovoltaic cell, and charge accumulation and screening occur. The model provides a simple estimate of the onset of the high injection regime in terms of the material resistivity and thickness, and provides a straightforward way to predict the EBIC lineshape in the high injection regime. The model is verified by comparing its predictions to numerical simulations in one- and two-dimensions. Features of the experimental data, such as the magnitude and position of maximum collection efficiency versus electron beam current, are consistent with the three-dimensional model.

High-Efficiency Plasmon-Enhanced and Graphene-Supported Semiconductor/Metal Core–Satellite Hetero-Nanocrystal Photocatalysts for Visible-Light Dye Photodegradation and H2 Production from Water

Solar-driven photocatalytic process based on electron-hole pair production in semiconductors is a long sought-after solution to a green and renewable energy and has attracted a renaissance of interest recently. The relatively low photocatalytic efficiency, however, is a main obstacle to their practical applications. A promising attempt to solve this problem is by combined use of metal nanoparticles, by taking advantage of strong and localized plasmonic near-field to enhance solar absorption and to increase the electron-hole pair generation rate at the surface of semiconductor. Here, we report a semiconductor/metal visible-light photocatalyst based on CdSe/CdS-Au (QD-Au) core-satellite heteronanocrystals, and assemble them on graphene nanosheets for better photocatalytic reaction. The as-synthesized photocatalyst exhibits excellent plasmon-enhanced photocatalytic activities toward both photodegradation of organic dye and visible-light H2 generation from water. The H2 evolution rate achieves a maximum of 3113 μmol h(-1) g(-1) for the heteronanocrystal-graphene composites, which is about 155% enhancement compared to nonplasmonic QD-G sample and 340% enhancement compared to control QD-Au-G sample, and the apparent quantum efficiency (QE) reaches to 25.4% at wavelength of 450 nm.

Integrated optical and electrical modeling of plasmon-enhanced thin film photovoltaics: A case-study on organic devices

The nanoscale light control for absorption enhancement of organic photovoltaic (OPV) devices inevitably produces strongly non-uniform optical fields. These non-uniformities due to the localized optical modes are a primary route toward absorption enhancement in OPV devices. Therefore, a rigorous modeling tool taking into account the spatial distribution of optical field and carrier generation is necessary. Presented here is a comprehensive numerical model to describe the coupled optical and electrical behavior of plasmon-enhanced polymer:fullerene bulk heterojunction (BHJ) solar cells. In this model, a position-dependent electron-hole pair generation rate that could become highly non-uniform due to photonic nanostructures is directly calculated from the optical simulations. By considering the absorption and plasmonic properties of nanophotonic gratings included in two different popular device architectures, and applying the Poisson, current continuity, and drift/diffusion equations, the model predicts quantum efficiency, short-circuit current density, and desired carrier mobility ratios for bulk heterojunction devices incorporating nanostructures for light management. In particular, the model predicts a significant degradation of device performance when the carrier species with lower mobility are generated far from the collecting electrode. Consequently, an inverted device architecture is preferred for materials with low hole mobility. This is especially true for devices that include plasmonic nanostructures. Additionally, due to the incorporation of a plasmonic nanostructure, we use simulations to theoretically predict absorption band broadening of a BHJ into energies below the band gap, resulting in a 4.8% increase in generated photocurrent.

Complete optoelectronic simulation of patterned silicon solar cells

In this paper, patterned silicon solar cells are fully modelled optically and electrically using Lumerical Solutions’ optical simulation software, FDTD Solutions and electrical simulation solver, DEVICE. The optical simulation calculates the spatial distribution of photon absorption in the silicon when the cell is illuminated by unpolarized sunlight with the AM1.5 solar spectral intensity. The photon absorption data is converted into a spatial generation rate of electron-hole pairs. The electrical simulation uses this generation rate to calculate the collection efficiency of electron and hole carriers, accurately accounting for surface and bulk recombination in silicon. Two main designs are simulated, each with periodic structures: a grating structure and a square pyramid structure. The short-circuit current as well as the overall conversion efficiency for the two devices are calculated.