Absorption Of High-energy Photons Research Articles

Optical Analysis of Perovskite III-V Nanowires Interpenetrated Tandem Solar Cells.

Multi-junction photovoltaics approaches are being explored to mitigate thermalization losses that occur in the absorption of high-energy photons. However, the design of tandem cells faces challenges such as light reflection and parasitic absorption. Nanostructures have emerged as promising solutions due to their anti-reflection properties, which enhances light absorption. III-V nanowires (NWs) solar cells can achieve strong power conversion efficiencies, offering the advantage of potentially integrating tunnel diodes within the same fabrication process. Metal halide perovskites (MHPs) have gained attention for their optoelectronic attributes and cost-effectiveness. Notably, both material classes allow for tunable bandgaps. This study explores the integration of MHPs with III-V NWs solar cells in both two-terminal and three-terminal configurations. Our primary focus lies in the optical analysis of a tandem design using III-V semiconductor nanowire arrays in combination with perovskites, highlighting their potential for tandem applications. The space offered by the compact footprint of NW arrays is used in an interpenetrated tandem structure. We systematically optimize the bottom cell, addressing reflectivity and parasitic absorption, and extend to a full tandem structure, considering experimentally feasible thicknesses. Simulation of a three-terminal structure highlights a potential increase in efficiency, decoupling the operating points of the subcells. The two-terminal analysis underscores the benefits of nanowires in reducing reflection and achieving a higher matched current between the top and the bottom cells. This research provides significant insights into NW tandem solar cell optics, enhancing our understanding of their potential to improve photovoltaic performance.

Efficient and Stable All-Polymer Solar Cells Enabled by Dual Working Mechanism.

Ternary strategy with integration characteristics and adaptability is a simple and effective method for blooming of the performance of photovoltaic devices. Herein, a novel wideband gap polymer donor PBB2-Hs is synthesized as the guest component to optimize all-polymer solar cells (all-PSCs). High-energy photon absorption and long exciton lifetime of PBB2-Hs constitute efficient energy transfer. Good miscibility and cascade energy levels promote the formation of alloy-like structure between PBB2-Hs and host system. The dual working mechanisms greatly improve photon capture and charge transfer in active layers. Additionally, the introduction of PBB2-Hs also optimizes the ordered molecular stacking of acceptors and suppresses molecular peristalsis. Upon adding 15 wt% PBB2-Hs, the ternary all-PSC achieved a champion efficiency of 17.66%, and can still maintain 82% photostability (24h) and 91% storage stability (1000h) of the original PCE. Moreover, the strong molecular stacking and entanglement between PBB2-Hs and the host material increased the elongation at break of ternary blend film by 1.6 times (16.2%), allowing the flexible device to maintain 83% of the original efficiency after 800 bends (R = 5mm). This work highlights the effectiveness of guest polymer on simultaneously improving photovoltaic performance, photostability and mechanical stability in all-PSCs.

Quasiparticle Poisoning of Superconducting Qubits from Resonant Absorption of Pair-Breaking Photons.

The ideal superconductor provides a pristine environment for the delicate states of a quantum computer: because there is an energy gap to excitations, there are no spurious modes with which the qubits can interact, causing irreversible decay of the quantum state. As a practical matter, however, there exists a high density of excitations out of the superconducting ground state even at ultralow temperature; these are known as quasiparticles. Observed quasiparticle densities are of order 1 μm^{-3}, tens of orders of magnitude greater than the equilibrium density expected from theory. Nonequilibrium quasiparticles extract energy from the qubit mode and can induce dephasing. Here we show that a dominant mechanism for quasiparticle poisoning is direct absorption of high-energy photons at the qubit junction. We use a Josephson junction-based photon source to controllably dose qubit circuits with millimeter-wave radiation, and we use an interferometric quantum gate sequence to reconstruct the charge parity of the qubit. We find that the structure of the qubit itself acts as a resonant antenna for millimeter-wave radiation, providing an efficient path for photons to generate quasiparticles. A deep understanding of this physics will pave the way to realization of next-generation superconducting qubits that are robust against quasiparticle poisoning.

Excitation-Selective and Double-Emissive Lead-Free Binary Hybrid Metal Halides for White Light-Emitting Diode and X-Ray Scintillation.

Zero-dimensional (0D) organic metal halides comprising heterogeneous metal cations in single phase can achieve multiple luminous emissions enabling them toward multifunctional light-emitting applications. Herein, A novel single crystal of (C8H20N)4SbMnCl9 containing two luminescent centers of [SbCl5]2- pentahedrons and [MnCl4]2- tetrahedrons is reported. The large distance between Sb-Sb, Mn-Mn, and Sb-Mn as well as theory calculation indicate negligible interaction between individual centers, thus endowing (C8H20N)4SbMnCl9 with excitation-dependable and efficient luminescence. Under near-UV excitation, only orange emission originates from self-trapped excitons recombination in [SbCl5]2- pentahedron occurs with photoluminescence quantum yield (PLQY) of 91.5%. Under blue-light excitation, only green emission originating from 4T1-6A1 transition of Mn2+ in [MnCl4]2- tetrahedrons occurs with PLQY of 66.8%. Interestingly, upon X-ray illumination, both emissions can be fully achieved due to the high-energy photon absorption. Consequently, (C8H20N)4SbMnCl9 is employed as phosphors to fabricate white light-emitting diodes optically pumped by n-UV chip and blue-chip thanks to its excitation-dependable property. Moreover, it also shows promising performance as X-ray scintillator with low detection limit of 60.79 nGyair S-1, steady-state light yield ≈54% of commerical scintillaotr LuAG:Ce, high resolution of 13.5 lpmm-1 for X-ray imaging. This work presents a new structural design to fabricate 0D hybrids with multicolor emissions.

Novel MCP-Windowed EUV Light Source and Its Mass Spectrometric Application for Detecting Chlorinated Methanes.

Various vacuum ultraviolet (VUV) lamps are simple and convenient VUV light sources for mass spectrometry and other research fields. However, the strong absorption of high-energy photons by window materials limits the application of an extreme ultraviolet (EUV) light. In this study, a novel high-flux EUV light source is developed using a microchannel plate (MCP) window to transmit 73.6 nm (16.9 eV) EUV light generated via the radio frequency (RF) inductive discharge of neon. The MCP used is a 0.5 mm thick glass plate with a regular array of microtubes (12 μm i.d.). The photon fluxes of the EUV light source with the MCP window (12 mm i.d.) and an aperture (1.8 mm i.d.) are ∼1.31 × 1014 and ∼9.80 × 1012 photons s-1, respectively, while their corresponding leakage flow rates of the discharge gas are 0.062 and 0.046 cm3 atom s-1, according to the contrast experiments. The transmission efficiency of the MCP to the EUV light is 30.2%, with a 1.2% deviation. An EUV photoionization time-of-flight mass spectrometer (EUV-PI-TOFMS) is built to validate the practicality of the MCP-windowed EUV light source further. The detection sensitivities in 30 s measurements for methyl chloride (CH3Cl), methylene chloride (CH2Cl2), trichloromethane (CHCl3), and carbon tetrachloride (CCl4) in synthetic air are 4366, 4120, 5854, and 4095 counts ppbv-1, respectively. The corresponding 3σ limits of detection (LODs) are 42, 34, 24, and 15 pptv. This study develops a new feasible method for efficiently utilizing high-energy EUV light, with many application prospects in scientific research.

Molecular-Orbital Framework of Two-Electron Processes: Application to Auger and Intermolecular Coulomb Decay.

States with core- or inner-shell vacancies, which are commonly created by absorption of high-energy photons, can decay by a two-electron process in which one electron fills the core hole and the second one is ejected. These processes accompany many X-ray spectroscopies. Depending on the nature of the initial core- or inner-shell-hole state and the decay valence-hole state, these processes are called Auger decay, intermolecular Coulomb decay, or electron-transfer-mediated decay. To connect many-body wave functions of the initial and final states with the molecular orbital picture of the decay, we introduce the concept of natural Auger orbitals (NAOs). NAOs are obtained by a two-step singular value decomposition of the two-body Dyson orbitals, reduced quantities that enter the expression of the decay rate in the Feshbach-Fano treatment. NAOs afford chemical insight and interpretation of the high-level ab initio calculations of Auger decay and related two-electron relaxation processes.

Review Article : Applicable methods of evaluating peak area of gamma ray spectra

Gamma ray spectra have interesting information about energy and intensity of gamma photons. Normally, this information is available in the peak area and background region. A full energy peak sits on a background continuum and produced by full energy absorption of high energy photons, while background region is produced by Compton scattering of the photons. The most essential concern of errors is in the method of determining the events in both peak and background areas. The uncertainty is low when the background counts are small relative to the peak counts. However, it becomes high when the counts of the peak area are low with respect to that of background. The detection threshold for the peak is ultimately determined by the uncertainty in the background counts. This depends on the technique used and the form of the produced spectra. This paper reviews different methods of determining peak area and their associated uncertainties in terms of the principle and application of the techniques used.

Harnessing Carrier Multiplication in Silicon Solar Cells Using UV Photons

Silicon solar cells are known to suffer from poor emitter performance that is seen as reduced external quantum efficiency at wavelengths below 500 nm. This is due to common tradeoff between electrical and optical performance. Here we demonstrate that no such tradeoff is needed when optimized boron implantation parameters are combined with non-reflective nanostructures and atomic layer deposited Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> surface passivation. As a result, in our solar cells the external quantum efficiency actually increases with decreasing wavelength and reaches even above 100% at short wavelengths. This result indicates that carrier multiplication caused by absorption of high energy photons could be utilized for energy production in solar cells.

Effect of varied number of multilayers, for cadmium sulphide with bismuth-doped zinc oxide buffer layer, on optical properties

Multilayer of Cadmium Sulphide (CdS) and Bismuth-doped Zinc Oxide (ZnO:Bi) is a direct band gap material, capable of use as a window layer material for silicon solar cells. With tuneable energy band gaps (2.41–2.71 eV)the ZnO:Bi/CdS window multilayer can allow for absorption of a wider range of wavelengths. This paper presents the varied number of ZnO:Bi/CdS multilayers and its effect on the optical properties. Samples were prepared using 3–11 layers of CdS and 3 layers of ZnO:Bi. Optical and structural properties were investigated through techniques including UV-Vis, XRD and FTIR analysis. Trends in energy band gaps were visible in relation to the number of layers used. The ZnO:Bi/CdS window layer demonstrated good absorption/transmission properties that make it a potential way of improving existing solar cell technology. Due to the high transmission rates, wavelengths of light (> Energy band gap of 1.1 eV) harnessed by Si cells, would not be hindered, while absorption of high energy photons (UV-Visible) can be improved on bulk Si solar cells.

Energy management in hybrid organic-silicon nanostructured solar cells by downshifting using CdZnS/ZnS and CdZnSe/ZnS quantum dots

Management of the solar spectrum by downshifting has been a key theme in broadband solar cell research over the last few years. The absorption of high-energy photons that exceed the bandgap edge of Si causes thermalization of charge carriers, which is a major loss mechanism by which collected energy is underutilized in silicon solar cells. The spectral response of Si also falls in the UV region. Progress in overcoming these effects achieved by modifying the input spectrum will dramatically enhance power conversion efficiency (PCE). Herein we report the application of highly luminescent CdZnS/ZnS and CdZnSe/ZnS quantum dots (QDs) as downshifting materials for nanostructured silicon. The applied QDs show major potential for shifting the high energy in the ultraviolet region to low energy, which is then transferred to the underlying silicon nanostructures via radiative and nonradiative energy transfer. This energy transfer dramatically improves the cell efficiency from 10.4% to 13.5%, showing this approach to be a reliable solution for improving solar cell properties. A Novel hybrid organic/inorganic silicon nanotips solar cell employing CdZnS/ZnS QDs as a downshifting layer which exhibits a drastic enhancement in the cell characteristics due to the radiative and nonradiative energy transfer (RET & NRET) from the QDs to underlying silicon nanostructure. • Highly emissive CdZnS/ZnS and CdZnSe/ZnS core/shell QDs were prepared by hot injection in two growth steps. • Silicon nanowires were fabricated by metal-catalyzed chemical etching and modified to tapered nanotip structure. • The current QDs show high potential for downshifting in hybrid silicon solar cells and improve the PCE to 13.49%.

Effect of Gold Nanoparticles on Optoelectronic Properties of Thermally Reduced Graphene Oxide

Gold nanoparticles (AuNPs)-decorated reduced graphene oxide (rGO) is a compelling material from both aspects of processing and functionality. This paper presents an alternative method to prepare and alter the optoelectronic properties of the AuNPs-rGO hybrid film. Au was sputtered for a duration of 0–60 s on graphene oxide (GO) film before subjected to thermal reduction at 700∘C. The surface of rGO was decorated by spherical AuNPs with a mean particle size of around 10[Formula: see text]nm due to the solid-state dewetting process. The surface plasmon resonance (SPR) of AuNPs around 550[Formula: see text]nm was intense when the Au sputter duration exceeded 20[Formula: see text]s. Remarkably, the AuNPs layer retarded the de-oxygenation of GO during thermal annealing. The AuNPs-rGO hybrid film with long-duration Au sputtering exhibited low optical constants and thicker rGO film. The AuNPs also played the role in lowering the bandgap, increasing the lattice disorder and assisting the high-energy photon absorption in the thermally reduced rGO film. The sample of 30[Formula: see text]s and 40[Formula: see text]s Au sputtering was optimum to obtain the lowest sheet resistance of 59[Formula: see text]k[Formula: see text]/sq and 56[Formula: see text]k[Formula: see text]/sq, respectively. The sheet resistance was bargained between de-oxygenation retardation and doping by the AuNPs. Both samples of 30 s and 40 s Au sputtering were having a unique and satisfyingly strong absorption band around 260[Formula: see text]nm, 350[Formula: see text]nm and 555[Formula: see text]nm corresponding to [Formula: see text]* transition, [Formula: see text]* transition and SPR of AuNPs, respectively. Such properties are desirable in several applications such as a transparent electrode and optoelectronic sensor.

Effect of SrF2:Pr3+-Yb3+ Nanophosphor on Downconversion of High Energy Photons for Efficient Dye-Sensitized Solar Cells

An emerging important class of photovoltaics for the next generation, the dye sensitized solar cells (DSSCs) has attracted great attention due to its low-cost, simple fabrication process and good performance. Though, one of the major loss mechanisms leads to lowering the power energy conversion efficiency is thermalization of charge carriers generated by the absorption of high energy photons. One promising novel strategy to decrease such thermalization loss is the use of downconversion (DC) luminescent materials as spectral converters. The rare-earth doped downshifting materials can converts higher energy photons into lower energy photons based on energy transfer from lanthanide ions to Yb3+ ions. In addition, the downconversion nanoparticles (DCNPs) are also act as scattering centers which can facilitates the light capture in photo-absorbing layer. With this aim, the rare earth doped downconversion SrF2: Pr3+-Yb3+ nanoparticles were synthesized by facile template free hydrothermal method. X-ray diffraction analysis confirms the formation cubic SrF2 phase. The prepared SrF2: Pr3+-Yb3+ down-shifting nanophosphor shows strong absorption in UV region and broad luminescence band emission in visible region evidenced from absorption and photoluminescence studies respectively. The enhancement in power conversion efficiency (PCE) was achieved by employing the synthesized downconverting nanomaterial as bottom layer in DSSC photoanode (Fig.1). The photovoltaic performance of the device was studied using standard solar simulator at 1 Sun intensity (AM 1.5 G) and DSSC with SrF2: Pr3+-Yb3+ shows improved efficiency of 9.066% than bare TiO2 based device (8.395%). The down-shifting nanophosphor material enhanced the efficiency of DSSC by 7.4% with 7.5% increment in photocurrent density compared to bare TiO2 based device. Figure 1

The origin of the power–law form of the extragalactic gamma–ray flux

The Fermi–LAT telescope has measured the extragalactic gamma–ray background (EGB) generated by the ensemble of all extragalactic sources. The energy distribution of the EGB is well described as a power–law with a spectral index approximately equal to 2.3, and an exponential cutoff, that is consistent with being the effect of absorption of high energy photons assuming an emission that is an unbroken power–law spectrum. The observations of the Fermi telescope have also resolved the EGB, determining that most of it is formed by the sum of the contributions of Active Galactic Nuclei (AGN) of the blazar class. The spectra of the individual AGN sources have a broad range of spectral shapes, and the brightest and most precisely measured sources have curved spectra that can be fitted with the “log–parabola” (or log–normal) form. This suggests that the power law form of the extragalactic gamma–ray flux emerges as a property of the ensemble of all sources, and not as a universal shape generated by each individual source. This result is consistent with the idea that particle acceleration in blazars can be considered as a “critical phenomenon”. A curved log–parabola (log–normal) form is also required to fit the spectra of many Galactic gamma–ray sources, including the emission from the brightest supernova remnants (SNR), and an intriguing possibility is that also the Galactic cosmic rays are injected in interstellar space by their sources not with a single universal power–law spectrum, as predicted by the commonly accepted models, but instead with a broad range of spectral shapes.

Phonon linewidths in InAs/AlSb superlattices derived from first-principles—application towards quantum well hot carrier solar cells

Hot electrons generated by the absorption of high-energy photons typically thermalize by dissipating energy through phonon mediated relaxation pathways. Existence of non-equilibrium optical phonon populations (hot phonons) can suppress thermalization of electrons by facilitating a stable hot carrier population. In this work, we derive optical phonon scattering rates in InAs/AlSb superlattices using first-principles calculations and compare them with bulk InAs. Computations are performed for the two shortest period superlattices with equal widths of InAs and AlSb. While in pure InAs, the highest optical phonon scattering rates reach 5 cm−1; in the superlattice, the peak scattering rates of optical phonons with frequencies above the energy gap, are much smaller, reaching ∼1 cm−1. These lower scattering rates in the superlattice have important implications for design of high efficiency hot carrier solar cells and explain some of the robust hot carriers observed recently in InAs/AlAsSb quantum wells.

Double-layer targets for forming the beams of the high-energy photons on the electron accelerator of M-30 microtron

Purpose. The bremsstrahlung received at electron accelerators is widely used to study the characteristics of photonuclear reactions and to solve a wide spectrum (series) of applied problems. Basically the output of bremsstrahlung depends on the electron energy, the material of the target converter (Ta) and its effective thickness. The optimum thickness of the converter (when the output of the bremsstrahlung is at its maximum) is significantly less than the electron path in it. This is the reason for the presence of high-energy electrons in bremsstrahlung. Therefore, there is a need to clean the bremsstrahlung beams from residual electrons. The aim of the work is to experimentally determine the optimal parameters (thicknesses) of double-layer targets for obtaining separated bremsstrahlung beams for an energy range of 6.5 – 17.75 MeV in electron accelerator M-30 microtron. Methods. Experimental studies of the relative absorption coefficient of electrons in the investigated materials (C (reactor graphite), Al, Ta) were carried out on the M-30 microtron using the transmission method. The measurements of the outputs of the electrons from the accelerator and the residuals that have passed through the layer of absorbing material were carried out using a pass-through chamber and a Faraday cup, respectively. Studies of the absorption of high-energy photons by single-layer targets (C (20 mm), Al (20 mm)) using activation detectors have been carried out. Results. The electron absorption coefficients in single- (C (7 – 46 mm), Al (8 – 48 mm), Ta (0.1 – 1 mm)) and in double-layer targets (Ta (1 mm) + C (7 – 39 mm) and Ta (1 mm) + Al (8 – 40 mm)) were measured for the electron energy 6.5 – 17.75 MeV. The values of the total electron absorption thickness for C, Al, and Ta are in good agreement with the calculated values of the practical electron path (database «ESTAR») for the indicated energy range. The experimentally established values of the thicknesses of materials (C and Al at a thickness of Ta – 1 mm) of doublelayer targets, which ensure the complete absorption of electrons for the indicated energy range. The absorption of high-energy photons by single-layer targets (C (20 mm), Al (20 mm)) for bremsstrahlung energy of 17.5 MeV was evaluated. Conclusions. The optimal parameters (thicknesses) of double-layer targets (Ta (1mm) + C (20 mm) and Ta (1 mm) + Al (20 mm)) or (Ta (1mm) + C (39 mm) and Ta (1 mm) + Al (32 mm)) were established experimentally to form the separated bremsstrahlung beams in the electron accelerator – M-30 microtron for energy region 6.5 ч 17.75 MeV. The use of two-layer targets allows us to carry out procedures to form of high-energy photon beams with the parameters necessary for performing specific experimental studies on electronic accelerators, which will increase the accuracy and reliability of the results.

Ultraviolet Photodissociation Mass Spectrometry for Analysis of Biological Molecules.

The development of new ion-activation/dissociation methods continues to be one of the most active areas of mass spectrometry owing to the broad applications of tandem mass spectrometry in the identification and structural characterization of molecules. This Review will showcase the impact of ultraviolet photodissociation (UVPD) as a frontier strategy for generating informative fragmentation patterns of ions, especially for biological molecules whose complicated structures, subtle modifications, and large sizes often impede molecular characterization. UVPD energizes ions via absorption of high-energy photons, which allows access to new dissociation pathways relative to more conventional ion-activation methods. Applications of UVPD for the analysis of peptides, proteins, lipids, and other classes of biologically relevant molecules are emphasized in this Review.

(Invited) The Impact of Defects on the Efficiency of Rare Earth Doped Oxides Under Vacuum Ultraviolet Excitation

Understanding the factors that govern efficient host-sensitized luminescence remains an important element in the development of more efficient luminescent materials. In a doped phosphor system, absorption of high energy photons leads to the creation of an electron-hole (e-h) pair in the host that must be captured by the dopant for emission to occur. While many materials have been developed for these applications, fundamental questions remain regarding the details of this energy transfer process. One aspect of research in this field that has not received much systematic attention is the study of the role various defects play in decreasing the efficiency of phosphors under host-sensitized excitation. The work presented here focuses on the effect of oxygen vacancies in rare earth doped YBO3 and YPO4, which are created via doping with Ca2+. Excitation and reflectance spectroscopy are combined to quantify the fraction of e-h pairs that are trapped by a dopant. The impact of oxygen vacancies depends on the particular rare earth present in the host, which is likely related to differences in the e-h trapping mechanism.

Double-layer targets for forming the beams of the high-energy photons on the electron accelerator of M-30 microtron

Purpose. The bremsstrahlung received at electron accelerators is widely used to study the characteristics of photonuclear reactions and to solve a wide spectrum (series) of applied problems. Basically the output of bremsstrahlung depends on the electron energy, the material of the target converter (Ta) and its effective thickness. The optimum thickness of the converter (when the output of the bremsstrahlung is at its maximum) is significantly less than the electron path in it. This is the reason for the presence of high-energy electrons in bremsstrahlung. Therefore, there is a need to clean the bremsstrahlung beams from residual electrons. The aim of the work is to experimentally determine the optimal parameters (thicknesses) of double-layer targets for obtaining separated bremsstrahlung beams for an energy range of 6.5 ÷ 17.75 MeV in electron accelerator M-30 microtron. Methods. Experimental studies of the relative absorption coefficient of electrons in the investigated materials (C (reactor graphite), Al, Ta) were carried out on the M-30 microtron using the transmission method. The measurements of the outputs of the electrons from the accelerator and the residuals that have passed through the layer of absorbing material were carried out using a pass-through chamber and a Faraday cup, respectively. Studies of the absorption of high-energy photons by single-layer targets (C (20 mm), Al (20 mm)) using activation detectors have been carried out. Results. The electron absorption coefficients in single- (C (7 ÷ 46 mm), Al (8 ÷ 48 mm), Ta (0.1 ÷ 1 mm)) and in double-layer targets (Ta (1 mm) + C (7 ÷ 39 mm) and Ta (1 mm) + Al (8 ÷ 40 mm)) were measured for the electron energy 6.5 ÷ 17.75 MeV. The values of the total electron absorption thickness for C, Al, and Ta are in good agreement with the calculated values of the practical electron path (database «ESTAR») for the indicated energy range. The experimentally established values of the thicknesses of materials (C and Al at a thickness of Ta – 1 mm) of doublelayer targets, which ensure the complete absorption of electrons for the indicated energy range. The absorption of high-energy photons by single-layer targets (C (20 mm), Al (20 mm)) for bremsstrahlung energy of 17.5 MeV was evaluated. Conclusions. The optimal parameters (thicknesses) of double-layer targets (Ta (1mm) + C (20 mm) and Ta (1 mm) + Al (20 mm)) or (Ta (1mm) + C (39 mm) and Ta (1 mm) + Al (32 mm)) were established experimentally to form the separated bremsstrahlung beams in the electron accelerator – M-30 microtron for energy region 6.5 ÷ 17.75 MeV. The use of two-layer targets allows us to carry out procedures to form of high-energy photon beams with the parameters necessary for performing specific experimental studies on electronic accelerators, which will increase the accuracy and reliability of the results

Modelling of Intrinsic Loss Processes in the Intermediate Band Solar Cells

Abstract For the first time, the formalism of intrinsic loss processes such as below-band gap, thermalisation, angle mismatch, Carnot and emission loss in the intermediate band solar cells (SCs) is obtained by a theoretical framework based on the principle of detailed balance approach, and with the physical origins of losses discussed in terms of photon absorption and emission in the presence of intermediate energy band (IB). Then, the effect of IB position on each intrinsic loss in the intermediate band SCs is investigated. The results show that the introduction of IB reduces the below-band gap loss due to absorption of low energy photons by narrower sub-band gap and reduces the thermalisation loss due to absorption of high energy photons by the band gap of host semiconductor. Furthermore, the thermalisation and angle mismatch losses are dominant fractions of intrinsic loss, while the emission loss presents less than 2.2 % of intrinsic loss.

Enhanced hot electron lifetimes in quantum wells with inhibited phonon coupling

Hot electrons established by the absorption of high-energy photons typically thermalize on a picosecond time scale in a semiconductor, dissipating energy via various phonon-mediated relaxation pathways. Here it is shown that a strong hot carrier distribution can be produced using a type-II quantum well structure. In such systems it is shown that the dominant hot carrier thermalization process is limited by the radiative recombination lifetime of electrons with reduced wavefunction overlap with holes. It is proposed that the subsequent reabsorption of acoustic and optical phonons is facilitated by a mismatch in phonon dispersions at the InAs-AlAsSb interface and serves to further stabilize hot electrons in this system. This lengthens the time scale for thermalization to nanoseconds and results in a hot electron distribution with a temperature of 490 K for a quantum well structure under steady-state illumination at room temperature.