Spectral Quantum Efficiency Research Articles

Improved Efficiency in WSe2 Solar Cells Using Amorphous InOx Heterocontacts.

van der Waals (vdW) layered materials have been shown to have excellent optoelectronic properties relevant to photovoltaics. Despite their promise, the demonstrated efficiencies of vdW material solar cells remain low and are seldom supported by statistics or spectral quantum efficiency analysis. In this study, we utilize a p-type WSe2 absorber, forming a solar cell with a transparent front InOx electron contact, and a rear Pd reflector/hole contact. We fabricate multiple devices providing statistics for 10 devices with an average 1 sun conversion efficiency above 5%, among which a champion efficiency of 6.37% is achieved. This is the highest AM 1.5G 1 sun efficiency reported for a vdW material solar cell, with a current density supported by external quantum efficiency analysis. This cell is also shown to have near unity quantum efficiency around λ = 600 nm. This work provides support to vdW materials being considered as serious candidates for future thin-film solar cells.

Systematic approach to measure the performance of microchannel-plate photomultipliers

In this paper, we present our approach to systematically measure numerous performance parameters of microchannel plate photomultiplier tubes. The experimental setups, the analyses and selected results are discussed. Although the techniques used may be different in other locations, the document is intended as a guide for comparable measurements with other types of microchannel plate photomultiplier tubes. Measurements are shown for the following performance parameters: spectral and spatial quantum efficiency, collection efficiency, gain as a function of voltage, position and magnetic field, time resolution, rate capability and lifetime. By using a dedicated 3-axis stepper and an FPGA-based data acquisition system, also inner PMT parameters are measured as a function of the active area, such as relative detection efficiency, dark count rate, time resolution, recoil electron and afterpulse distributions, as well as charge sharing and electronic crosstalk. In addition, some of the parameters are investigated inside a strong magnetic field. For many of these measurements, the change of most setup parameters and the subsequent analysis can be controlled semi-automatically by software scripts.

Independently Accessible Dual-Band Barrier Infrared Detector Using Type-II Superlattices

We report a novel dual-band barrier infrared detector (DBIRD) design using InAs/GaSb type-II superlattices (T2SLs). The DBIRD structure consists of back-to-back barrier diodes: a “blue channel” (BC) diode which has an nBp architecture, an n-type layer of a larger bandgap for absorbing the blue band infrared/barrier/p-type layer, and a “red channel” (RC) diode which has a pBn architecture, a p-type layer of a smaller bandgap for absorbing the red band infrared/barrier/n-type layer. Each has a unipolar barrier using a T2SL lattice matched to a GaSb substrate to impede the flow of majority carriers from the absorbing layer. Each channel in the DBIRD can be independently accessed with a low bias voltage as is preferable for high-speed thermal imaging. The device modeling of DBIRDs and simulation results of the current–voltage characteristics under dark and illuminated conditions are also presented. They predict that the dual-band operation of the DBIRD will produce low dark currents and 45–56% quantum efficiencies for the in-band photons in the BC with λc = 5.58 μm, and a nearly constant 32% in the RC with λc = 8.05 μm. The spectral quantum efficiency of the BC for 500 K blackbody radiation is approximately 50% over the range of λ = 3–4.7 μm, while that of the RC has a peak of 42% at 5.9 μm. The DBIRD may provide improved high-speed dual-band imaging in comparison with NBn dual-band detectors.

A Steady-State Spectral Response and Quantum Efficiency Determination of a Bifacial Silicon Solar Cell under Monochromatic Illumination and Constant Magnetic Field Effects by Using the Photoconductivity Method

A Steady-State Spectral Response and Quantum Efficiency Determination of a Bifacial Silicon Solar Cell under Monochromatic Illumination and Constant Magnetic Field Effects by Using the Photoconductivity Method

Comparative study of commercial crystalline solar cells

In this research article, a comparative study of different types, i.e., conventional (Multicrystalline & Monocrystalline) and Passivated Emitter Rear Cell (PERC) of commercially available crystalline silicon solar cells have been carried out in terms of their spectral response (SR), quantum efficiency (QE) and current–voltage (I-V) characteristics. The SR, Internal Quantum Efficiency (IQE), and External Quantum Efficiency (EQE) measurements have been utilized for analyzing the internal parameters such as diffusion length (L) and dead layer (dl) thickness values in all types of solar cells using Medium Wavelength Spectral Response (MWSR) and Short Wavelength Spectral Response (SWSR) methods respectively. The effect of surface passivation on the diffusion length has also been studied for mono, multi, and PERC crystalline solar cells. The results indicate that the PERC solar cells have a higher L and lower dl value and the probable reason for the high performance of this technology. The different types of solar cells are also converted into modules, and the I-V characterization is done with the Sun simulator and indicates the high performance of PERC modules. The paper also highlights one of the probable reasons for the recent PV market shift towards PERC technology.

Modulating the Quantum Efficiency of Sb2S3‐Based Photodiodes Based on Conventional and Inverted Structures

AbstractAntimony sulfide (Sb2S3), a binary chalcogenide, has recently emerged as a promising candidate for photovoltaics due to its high absorption coefficient, facile processing, and lower toxicity. However, high‐performance photodiodes based on Sb2S3 have not been achieved and systematically investigated. Herein, Sb2S3‐based photodiodes based on conventional and inverted structures are developed, and their charge transport and spectral dependent quantum efficiency of these two types of devices are carefully modulated. After optimization, the conventional photodetectors achieve broadband responsivity up to 0.3 A W−1, high specific detectivity of 1.25 × 1012 Jones, and fast response speed of 6.4 µs with a small bias voltage of −0.5 V. On the other hand, the inverted devices exhibit imbalanced charge transport and color discrimination, which is promising for narrowband photodetection. These distinct device performances are highly dependent on the device architecture, which is crucial for designing efficient chalcogenide‐based optoelectronic devices.

Manufacturing Br:CO3O4 /Si Heterojunction For Photodetector Applications

This research including, CO3O4 was prepared by the chemical spry pyrolysis, deposited film acceptable to assess film properties and applications as photodetector devise, studying the optical and optoelectronics properties of Cobalt Oxide and effect of different doping ratios with Br (2, 5, 8)%. the optical energy gap for direct transition were evaluated and it decreases as the percentage Br increase, Hall measurements showed that all the films are p-type, the current–voltage characteristic of Br:CO3O4 /Si Heterojunction show change forward current at dark varies with applied voltage, high spectral response, specific detectivity and quantum efficiency of CO3O4 /Si detector with 8% of Br ,was deliberate, extreme value with 673nm.

Modeling electron transport and multiplication in photomultiplier tubes using COMSOL Multiphysics®

Combining stochastic and finite element methods, a modeling approach was executed that will inform new photomultiplier tube and scintillation detector designs. Time-dependent signal formation within a commercially available photomultiplier tube was modeled including the release and transport of electrons from the photocathode through the dynode stages. An ET Enterprises 9214B photomultiplier tube was digitally reproduced using Computed Tomography, X-ray radiography, and SolidWorks solid-modeling software. Simulations were executed with COMSOL Multiphysics® finite element solving package. Stochastic models of electron emission from the photocathode and dynodes were integrated within the COMSOL framework. Photoelectron emission energy was modeled by combining NaI(Tl) spectral emission characteristics and K2CsSb photocathode quantum efficiency. Secondary electron emission yields were produced to follow nominal photomultiplier gain, while secondary electron energies were sampled from the Chung-Everhart distribution. Electron emission trajectories were sampled according to Lambert's cosine law. Coupling stochastic and finite element models, simulation reproduced signal formation for the commercial photomultiplier tube including timing characteristics within 9.5% and gain within 3% over a voltage range of 900–1250 V.

Systematic Crystallization of NH4Ln(MoO4)2 as a Family of Layered Compounds (Ln = La-Lu and Y), Derivation of Ln2Mo4O15, Crystal Structure, and Photoluminescence.

NH4Ln(MoO4)2 (Ln = La-Lu lanthanide, Y) was crystallized via hydrothermal reaction as a new family of layered materials, from which phase-pure Ln2Mo4O15 was successfully derived via subsequent annealing at 700 °C for the series of Ln elements excluding Ce and Lu. Detailed structure analysis revealed that the ionic size of Ln3+ decisively determined the crystal structure and Mo/Ln coordination for the two families of compounds. NH4Ln(MoO4)2 was analyzed to be orthorhombic (Pbcn space group, no. 60) and monoclinic (P2/c, no. 13) for the larger and smaller Ln3+ of Ln = La-Gd and Ln = Tb-Lu (including Y), respectively, where both the crystal structures have a layered topology featured by the alternative stacking of a [Ln(MoO4)2]- three-tier infinite anionic layer and interlayer NH4+. Four types of crystal structures were found for the Ln2Mo4O15 series, which are monoclinic (P21/a, no. 14) for Ln = La, triclinic (P1̅, no. 2) for Ln = Pr-Sm, triclinic (P1̅, no. 2) for Ln = Eu and Gd, and monoclinic (P21/c, no. 14) for Ln = Tb-Yb (including Y). The photoluminescence of NH4Ln(MoO4)2 (Ln = Eu, Tb) and Ln2Mo4O15:Eu3+ (Ln = La, Gd, Y) was thoroughly investigated in terms of spectral features, quantum efficiency, fluorescence decay, and CIE chromaticity. The thermal stability of luminescence was also studied for Ln2Mo4O15:Eu3+, and the observed charge-transfer excitation components were successfully correlated with the features of the Mo-O polyhedron/unit.

Apparatus for Calibration of Photovoltaic Cells at National Institute of Standards

The Egyptian National Institute of Standards (NIS) has established and developed a system for calibrating reference solar cells using photodiode detectors traceable to the absolute cryogenic radiometer (ACR). This research discusses an experimental procedure for measuring spectral responsivity, external quantum efficiency, and internal quantum efficiency of reference solar cells from the range of 340 nm to 930 nm. The associated uncertainty budget is also estimated. Additionally, this paper shows the NIS's calibration facility for pyranometers at different irradiance levels (200 W/m², 800W/m², and 1000W/m²). The measurement of the spectral responsivity and quantum efficiency of reference solar cells using two techniques is converged with each other with an uncertainty of about ±1% (at 900 nm). Also, the sensitivity of the pyranometer at 800W/m² is 15.97µV/W/m² ±1.9%.

Effect of nitrogen on the properties of nanostructured zinc nitride heterojunction prepared by reactive magnetron sputtering

In this work, zinc nitride (Zn3N2) thin film was deposited on glass and silicon substrates by DC reactive magnetron sputtering technique. The structural, optical and electrical properties of Zn3N2 films at various nitrogen gas concentration were investigated. XRD results of the as-deposited films confirm the formation of crystalline cubic anti-bixbyite Zn3N2 structure with a preferred orientation along (400) plane. AFM and SEM have used to study the surface topography and morphology of the deposited film. Raman analysis of the as-grown films show two broad peaks at 265 and 567 cm−1 related to the Raman-active modes in the Zn3N2 compound. The highest optical transmittance of the film was 62% for the film deposited with pure nitrogen and decreased to 1% at 40% N2. There was a blueshift in the absorption edge with increasing the N2 gas concentration. The direct optical band gap of the films ranged from 1.27 to 2.1 eV with increasing N2 gas flow. The I–V characteristics of Zn3N2/p-Si heterojunctions showed rectification characteristics. C–V results showed that the built-in-potential of the heterojunctions was in the range of 0.51–0.82V. A broad responsivity has been observed for all of Zn3N2/p-Si heterojunction photodetectors and the highest spectral responsivity and quantum efficiency of the photodetector are 0.15 A/W and 35% at 600 nm, respectively.

Quantum Efficiency and Crosstalk in Subwavelength HgCdTe Dual Band Infrared Detectors

This work investigates the spectral quantum efficiency and inter-pixel crosstalk of a MWIR-LWIR dual band, HgCdTe-based focal plane array (FPA) photodetector (MWIR and LWIR stand for mid- and long-wavelength infrared bands). Pixels are 10 μm-wide with truncated pyramid geometry and separated by deep trenches. Three-dimensional combined full-wave electromagnetic and electrical simulations in the drift-diffusion approximation allowed to describe the complex, standing-wave-like spectral features resulting from the light interference and diffraction due to the pixels and illuminating beam aperture. The inter-pixel crosstalk for the MWIR operation demonstrated to be very sensitive to the trench depth, in contrast to the LWIR electrooptical response, left almost unchanged. The present work also investigates the causes of performance worsening in the two IR bands when pixel pitch is reduced to 5 μm, hence well below typical LWIR wavelengths and close to the diffraction limited operation.

SiOx films deposited by HFCVD: Their conduction response to light and intrinsic photovoltaic effect

In this work, the presence of photoconduction and photovoltaic effects in MOS-type structures manufactured using off-stoichiometric silicon oxide (SiOx) deposited by HFCVD technique is reported. Current-voltage measurements under dark and illumination conditions were carried out. A photoconductive response of 1µA was found under illumination conditions, such current is about 4 orders of magnitude greater than its value in dark condition which was about 100pA. The reported MOS-type structures with SiOx as dielectric layer undergo a change in the charge conduction mechanisms of the injection current, exhibiting a transition from the Hopping to Schottky mechanism, which is dependent on the hydrogen amount and the deposition parameters of SiOx films. A starting charge conduction state identified as the Space Charge Limited Conduction mechanism (SCLC) is found when applying low voltages. Additionally, the photovoltaic effect was obtained and studied for these types of structures, being corroborated by current-time and voltage-time measurements in dark and illuminations conditions without applied bias. The spectral response and quantum efficiencies were also obtained, where the best internal quantum efficiency was 25.59%. The photoconductive effect is present for structures with SiOx films without annealing, while the ones with SiOx films that have thermal annealing exhibit the photovoltaic effect. The studied structures are suitable for photovoltaic applications and they have additional advantages namely: a short time of deposit (3 min) by using the HFCVD technique, and a single MOS-type structure.

Commercial-off-the-shelf event-based cameras for space surveillance applications

Event-based cameras (EBCs) are of interest for potential application to space domain awareness (SDA). EBC attributes, including asynchronous response and low latency provide data reduction, break the trade-off between latency and power, and enable consideration of additional algorithms and processing architectures due to individual timestamps for each event. Potential data reduction by a factor of 10 or greater is particularly attractive for SDA from satellite platforms with constraints on system power, processing, and communication bandwidth. Here we report our initial evaluation of Prophesee third-generation commercial-off-the-shelf (COTS) EBCs, including development of, and comparison with, a limiting magnitude model. The analytic model is a function of sky background radiance; EBC parameters including contrast threshold, dark current, pixel pitch, and spectral quantum efficiency; and the optic aperture diameter and focal length. Using an 85 mm f/1.4 lens, the measured detection limits for the half-size video graphics array (HVGA) and video graphics array (VGA)-format EBCs are 6.9 and 9.8 visual magnitudes (mV), respectively, at a sky background level of about 20.3mV per square arcsecond. The empirical sensitivity limit for the VGA differs by 0.1mV from our analytic prediction of 9.7 (less than 10% difference in flux). The limiting magnitude model assumes slow motion of point objects across the EBC focal plane array. Additional experiments exploring temporal behavior show that no stars are detected while scanning across the night sky faster than 0.5 deg per second using the VGA-EBC mounted to a 200 mm f/2.0 lens. The limited sensitivity of the evaluated COTS EBCs prevents their use as a replacement for typical CCD/CMOS framing sensors, but EBCs show clear promise for small-aperture, large-field persistent SDA in terms of their efficient capture of temporal information.

InAsSb-based detectors on GaSb for near-room-temperature operation in the mid-wave infrared

III-Sb barrier detectors suitable for the mid-wave infrared were grown on GaSb by molecular beam epitaxy. Using both bulk-InAsSb and an InAsSb–InAs strained layer superlattice, operation close to room temperature was demonstrated with cutoff wavelengths of 4.82 and 5.79 μm, respectively, with zero-bias operation possible for the bulk-InAsSb detector. X-ray diffraction, temperature dependent dark current, and spectral quantum efficiency were measured, and an analysis based on calculated specific detectivity was carried out. 1/f noise effects are considered. Results indicate that these optimized devices may be suitable as alternatives to InSb, or even HgCdTe, for many applications, especially where available power is limited.

Study The Responsory And Quantum Efficiency of Silicon P-N Junction by Using Pulse Plasma

In this work we have used plasma pulsed injector to prepare a P-N junction. Antimony was deposited on P-type silicon wafer and Indium was deposited on N-type silicon wafer. They were considered as thin film which was bombarded with accelerated hydrogen-ions from the pulsed plasma injector. Optical tests were conducted for the both junctions to evaluate their performance as optical detectors. These include the spectral response quantum efficiency and detectivity. They showed high response and efficiency for the long wavelength in the near IR region. It showed a relatively higher detectivity which increased with the number of discharges. For antimony and indium implanted samples we have noticed an increase in the response time of the detector with the number of discharges. These findings allow the possibility to use them in the near IR-detector and semiconductor lasers in the wavelength range 850-950nm as well as in the applications of optical communication systems. This work also revealed the possibility of using the pulsed plasma injection to modify the material surfaces as well as the ultering the semiconductor surfaces.

Establishment and evaluation of photovoltaic quantum efficiency system at central metallurgical research and development institute

A system for measuring the spectral responsivity and quantum efficiency of solar cells is described. We have developed and characterized a traceable measurement setup for measuring the spectral responsivity S(λ) and photovoltaic quantum efficiency at Central Metallurgical Research and Development Institute (CMRDI); we report experimental measurements for spectral responsivity, reflectance, and quantum efficiency measurements covering the wavelength from 300 nm to 1800 nm. For this purpose, we adapted and improved a system designed to measure the External Quantum Efficiency (EQE) and the Internal Quantum Efficiency (IQE) of different types of solar cells as the determination of the spectral responsivity is an essential part of solar cell characterization. Furthermore, this research discusses a procedure for measuring the spectral responsivity of Si and InGeAs detectors used as a reference cell for spectral responsivity and photovoltaic quantum efficiency measurements of solar cells. The system construction and its associated uncertainty budget are described as estimated in detail.

Photoelectric properties of SnO2: Ag/P–Si heterojunction photodetector

N-type Tin dioxide thin films with thickness (350 nm) prepared by thermal evaporation method. The thin film SnO2 was doped with Ag by the rate (0.01, 0.02 and 0.03). Atomic Force Microscopic (AFM) was adopted to determine the grain size and roughness of the film surface. The electrical properties were determined by mean of Hall Measurement system and mobility was calculated. SnO2: Ag/P–Si​ photodetectors demonstration the highest described visible responsivity of (0.287 A/W) with the Ag ratio of (0.03). I–V characteristics with different power density were measured. The best sensitive value of the spectral response, specific detectivity and quantum efficiency at wavelength (422 nm).

Current Noise and Efficiency Droop of Light-Emitting Diodes in Defect-Assisted Carrier Tunneling from an InGaN/GaN Quantum Well

The current dependences of the spectral noise density and quantum efficiency in green and blue light-emitting diodes with InGaN/GaN quantum wells (QWs) are measured. It is shown that the noise level greatly increases at high currents at which there is a quantum efficiency droop. The mechanism by which the current noise is formed is associated with hopping transport via the deep states of color centers in GaN across the n barrier of an InGaN/GaN QW. The source of the noise is the hopping resistance of the space-charge region, which limits the current of thermally activated electrons into the QW. The efficiency droop and the increase in noise level are attributed to a change in the electric-field direction near the QW at high injection levels and to an increase in the tunneling leakage of holes from the QW. It is shown that the experimental frequency-related noise spectra having the shape of a Lorentzian spectrum at the working currents are related to the frequency of hopping between deep centers near the InGaN/GaN QW and to Maxwell relaxation in the space-charge region.

Токовый шум и падение эффективности светодиодов при туннелировании носителей из квантовой ямы InGaN/GaN с участием дефектов

AbstractThe current dependences of the spectral noise density and quantum efficiency in green and blue light-emitting diodes with InGaN/GaN quantum wells (QWs) are measured. It is shown that the noise level greatly increases at high currents at which there is a quantum efficiency droop. The mechanism by which the current noise is formed is associated with hopping transport via the deep states of color centers in GaN across the n barrier of an InGaN/GaN QW. The source of the noise is the hopping resistance of the space-charge region, which limits the current of thermally activated electrons into the QW. The efficiency droop and the increase in noise level are attributed to a change in the electric-field direction near the QW at high injection levels and to an increase in the tunneling leakage of holes from the QW. It is shown that the experimental frequency-related noise spectra having the shape of a Lorentzian spectrum at the working currents are related to the frequency of hopping between deep centers near the InGaN/GaN QW and to Maxwell relaxation in the space-charge region.