Monochromatic Efficiency Research Articles

Ge-Based Photovoltaic Laser-Power Converters

The Ge-based photovoltaic laser-power converters (LPCs) for wireless IR energy delivery approach with a wavelength of λ = 1550 nm are studied and developed. It is shown that the doping by diffusion from the gas phase with zinc gives rise to a notable increase in photosensitivity compared with the doping with diborane, phosphine, or antimony (including for two-stage diffusion technology). Four designs and areas of converters are fabricated and investigated under Xe flash lamp, defocused and focused laser beams. For LPCs with an area of 6.25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , a monochromatic efficiency of ∼20% (0.2 W) is obtained at uniform irradiation.

Band-gap material selection for remote high-power laser transmission

High-power laser transmission (HPLT) is attracting a huge interest from both the scientific and industrial community due to its large number of potential applications and future perspectives. This technology consists of the use of a monochromatic light source to power supply a remote system by using a photovoltaic converter. HPLT offers a technological paradigm shift with the possibility of transmitting kilowatts to several kilometres without the use of wires. However, HPLT is still under development and the current efficiency, ≈20%, needs to be improved to achieve the actual potential of the technology. This work is focused on the investigation of the most suitable materials to improve the performance of HPLT systems under a wide range of scenarios. For the first time, the monochromatic efficiency of PV converters, considering the attenuation of the atmosphere with the distance, and for various input light intensities and series resistance scenarios, is deeply investigated. The results indicate that high energy gap materials such as ZnS (3.54 eV) or 6H–SiC (3 eV) could lead to record efficiencies and improve current values in more than 30%. We have investigated the most suitable band-gap materials to transfer kilowatts of laser power to remote systems considering a wide range of scenarios, i.e. energy gap, series resistance, laser power, atmosphere and distance. Our results indicate the high energy gap materials (>2 eV) such as ZnS, SiC, AlP, CdS or InN offer a novel route to improve the efficiency of high-power laser transmission in more than 30%. • The suitable band-gap materials for remote laser high-power are investigated. • Different scenario of energy gap, series resistance and power are selected. • The spectral attenuation of the atmosphere with distance is considered. • High energy gap materials could improve the efficiency in more than 30%.

Module of Laser-Radiation (λ = 1064 nm) Photovoltaic Converters

The results of a study and the development of a module designed for energy transmission via atmospheric channels are presented. The four-cell module based on single-junction metamorphic InGaAs/GaAs converters grown by metal-organic vapor-phase epitaxy has an open-circuit voltage of ~3 V. It is shown that the monochromatic efficiency (at a wavelength of 1064 nm) of this module is 31.5% under exposure to a Xe-lamp with a radiation power of 1.5 W/cm2.

Модуль фотоэлектрических преобразователей лазерного излучения (&amp;lambda;=1064 нм)

AbstractThe results of a study and the development of a module designed for energy transmission via atmospheric channels are presented. The four-cell module based on single-junction metamorphic InGaAs/GaAs converters grown by metal-organic vapor-phase epitaxy has an open-circuit voltage of ~3 V. It is shown that the monochromatic efficiency (at a wavelength of 1064 nm) of this module is 31.5% under exposure to a Xe-lamp with a radiation power of 1.5 W/cm^2.

Modification of Photovoltaic Laser-Power (λ = 808 nm) Converters Grown by LPE

Laser-power converters for the wavelength λ = 808 nm are fabricated by liquid-phase epitaxy (LPE) on the basis of n-Al0.07GaAs–p-Al0.07GaAs–p-Al0.25GaAs single-junction heterostructures. The converters are tested with uniform (pulse simulator) and partly nonuniform (laser beam) illumination distribution over the photoreceiving surface. In the former case, a monochromatic efficiency of η = 53.1% is achieved for samples with an area of S = 4 cm2 at a power of 1.2 W. At S = 10.2 mm2 the efficiency is 58.3% at a laser power of 0.7 W.

Модификация фотоэлектрических преобразователей лазерного излучения (lambda=808 нм), получaемых методом жидкофазной эпитаксии

AbstractLaser-power converters for the wavelength λ = 808 nm are fabricated by liquid-phase epitaxy (LPE) on the basis of n -Al_0.07GaAs– p -Al_0.07GaAs– p -Al_0.25GaAs single-junction heterostructures. The converters are tested with uniform (pulse simulator) and partly nonuniform (laser beam) illumination distribution over the photoreceiving surface. In the former case, a monochromatic efficiency of η = 53.1% is achieved for samples with an area of S = 4 cm^2 at a power of 1.2 W. At S = 10.2 mm^2 the efficiency is 58.3% at a laser power of 0.7 W.

GaSb laser-power (λ = 1550 nm) converters: Fabrication method and characteristics

Photovoltaic converters of laser light with a wavelength of λ = 1550 nm are developed using liquidphase epitaxy (LPE), metal-organic chemical-vapor deposition (MOCVD), and diffusion from the gas phase into the n-GaSb substrate. Photocells with an area of S of 4, 12.2, and 100 mm2 are fabricated and tested. The characteristics of the samples produced by different methods are compared. The monochromatic efficiency is found to be 38.7% for the best converters (with S = 12.2 mm2) at a laser power of 1.4 W.

Photovoltaic laser-power converter based on AlGaAs/GaAs heterostructures

Photovoltaic laser-power converters for a wavelength of λ = 809 nm are developed and fabricated on the basis of single-junction AlGaAs/GaAs structures grown by metal-organic vapor-phase epitaxy. The parameters of the photovoltaic structure constituted by an optical “window” and a cladding layer are optimized by mathematical simulation. Photovoltaic converters with areas of S = 10.2 and 12.2 mm2 and 4 cm2 are fabricated and studied. For photocells with S = 10.2 mm2, the monochromatic efficiency (η) was 60% at a current density of 5.9 A/cm2. A photovoltaic module with a working voltage of 4 V (η = 56.3% at 0.34 A/cm2) is assembled.

Sensor Correction of a 6-Band Multispectral Imaging Sensor for UAV Remote Sensing

Unmanned aerial vehicles (UAVs) represent a quickly evolving technology, broadening the availability of remote sensing tools to small-scale research groups across a variety of scientific fields. Development of UAV platforms requires broad technical skills covering platform development, data post-processing, and image analysis. UAV development is constrained by a need to balance technological accessibility, flexibility in application and quality in image data. In this study, the quality of UAV imagery acquired by a miniature 6-band multispectral imaging sensor was improved through the application of practical image-based sensor correction techniques. Three major components of sensor correction were focused upon: noise reduction, sensor-based modification of incoming radiance, and lens distortion. Sensor noise was reduced through the use of dark offset imagery. Sensor modifications through the effects of filter transmission rates, the relative monochromatic efficiency of the sensor and the effects of vignetting were removed through a combination of spatially/spectrally dependent correction factors. Lens distortion was reduced through the implementation of the Brown–Conrady model. Data post-processing serves dual roles in data quality improvement, and the identification of platform limitations and sensor idiosyncrasies. The proposed corrections improve the quality of the raw multispectral imagery, facilitating subsequent quantitative image analysis.

π-Conjugated molecular heterojunctions with multi[60]fullerene: photophysical, electrochemical, and photovoltaic properties

A series of well-defined D–π-B–A C60 adducts containing three chromophores and their corresponding precursors were facilely developed as organic photovoltaic materials. The photophysical and electrochemical properties indicated that effective photo-induced intramolecular and/or intermolecular energy transfer and charge transfer were formed from the donor chromophores to the C60 moiety in thin films. Solution processed molecular heterojunction solar cells using 12 as active layer were fabricated with 2.0% monochromatic efficiency. Our results showed that further exploration might lead the way toward high-efficient solution-processed single molecular solar cell materials based on conjugated oligomer covalent to fullerene units.

High-Voltage GaAs Photovoltaic Laser Power Converters

The main drawback of photovoltaic (PV) laser power converters based on GaAs material is the low output voltage, which is often insufficient to power electronic circuits directly. Aside from the use of a dc-dc converter in combination with a single PV converter, it is possible to boost the voltage by the monolithic serial interconnection of several converter segments on a single chip, often called multiple converters. Another novel approach introduced in this paper is a multijunction PV cell, where several subcells of the same material are stacked onto a substrate and interconnected by interband tunnel diodes. This paper explores a tandem GaAs-GaAs converter and compares the results with a 2-V multiple PV converter under monochromatic laser illumination. In addition, 4-V multiple PV converters with maximum monochromatic efficiencies (810 nm) of up to 50.1% at 51.6 W/cm2 and 6-V converters are investigated. Thereby, the fabrication technology of the devices is outlined and the influence of inhomogeneous illumination on the performance of these energy converters is discussed.

Correlation between spatially resolved solar cell efficiency and carrier lifetime of multicrystalline silicon

The correlation between the spatially resolved carrier lifetime of multicrystalline silicon and the spatially resolved monochromatic solar cell efficiency is investigated by means of microwave-detected photoconductance decay (MW-PCD) measurements and illuminated lock-in thermography (ILIT). Local monochromatic solar cell efficiencies are determined from ILIT measurements under short-circuit conditions and at the maximum power point of the cell. The resulting efficiency images are compared with efficiency images obtained from MW-PCD lifetime images of unprocessed neighbouring wafers using PC1D simulations. We observe a qualitative correlation between the measured and the simulated efficiency images. Areas with reduced efficiency are found in the same locations using both methods. However, the dynamic range in the monochromatic efficiency is larger for the images obtained from ILIT measurements. Possible explanations for this difference are a change in carrier lifetime during cell processing and varying lifetimes on microscopic scales, leading to averaging faults in the lifetime images.

Carbon Nanotubes in Electron Donor—Acceptor Nanocomposites

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Carbon Nanotubes in Electron Donor−Acceptor Nanocomposites

This Account presents recent advances in the design, synthesis, characterization, and potential applications of new hybrid materials based on carbon nanotube and electron donors. Fast charge separation and slow charge recombination are consistently observed in a variety of composites that contain porphyrin derivatives. The ultimate goal of using these systems to prepare practical photoelectrochemical devices is discussed, and a cell with a monochromatic efficiency of 8.5% conversion of light into current is illustrated.

Eu이 도핑된 LiGdF4의 Down-conversion을 이용한 염료감응형 태양전지의 효율 향상

Down-conversion of Eu<TEX>$^{3+}$</TEX> doped LiGdF<TEX>$_4$</TEX> (LGF) for increasing the cell efficiency on dye-sensitized Ti <TEX>$O_2$</TEX> solar cells has been studied. The dye sensitized solar cell (DSC) consisting of mesoporous Ti <TEX>$O_2$</TEX> electrode deposited on transparent substrate, an electrolyte containing I<TEX>$^{[-10]}$</TEX> /I<TEX>$_3$</TEX><TEX>$^{[-10]}$</TEX> redox couple, and Pt counter electrode is a promising alternative to the inorganic solar cell. The structure of DSC is basically a sandwich type, viz., FTO glass/Ru-red dye-absorbed Ti <TEX>$O_2$</TEX>/iodine electrolyte/sputtered Pt/FTO glass. The cell without down converter had open circuit potential of approximately 0.66 Volt, the short circuit photocurrent density of 1.632 mA/<TEX>$\textrm{cm}^2$</TEX>, and fill factor of about 50 ％ at the excitation wavelength of 550 nm. In addition, 5.6 mW/<TEX>$\textrm{cm}^2$</TEX> incident light intensity beam was used as a light source. From this result, the calculated monochromatic efficiency at the wavelength of 550 nm of this cell was about 9.62 ％. The incident photon to current conversion efficiency (IPCE) of N3 used as a dye in this work is about 80 ％ at around 590 nm and 610 nm, which is the emission spectrum of Eu<TEX>$^{3+}$</TEX> doped LGF, results in efficiency increasing of DSC.C.

Molecular engineering of C60-based conjugated oligomer ensembles: modulating the competition between photoinduced energy and electron transfer processes.

A series of novel and soluble C60-(pi-conjugated oligomer) dyads were synthesized, starting from suitably functionalized oligomer precursors (i.e., dihexyloxynaphthalene, dihexyloxynaphthalene-thiophene, and dihexyloxybenzene-thiophene). A systematic change in the nature of the oligomeric component allowed (i) tailoring the light absorption of the chromophore by shifting the ground-state absorption from the ultraviolet to the visible region and (ii) varying the oxidation potential of the donor. The resulting electro- and photoactive dyads were examined by electrochemical and photophysical means. In general, both singlet-singlet energy transfer and intramolecular electron transfer were found to take place and, most importantly, to compete with each other in the overall deactivation of the photoexcited oligomer. The selection of polar solvents in combination with the dihexyloxybenzene-thiophene donor shifted the reactivity from an all energy (1a; dihexyloxynaphthalene) to an all electron-transfer scenario (1d, dihexyloxybenzene-thiophene). Encouraged by the favorable electron-transfer properties of dyad 1d, we prepared photodiodes by embedding 1d between asymmetric metal contacts, which showed external monochromatic efficiencies (IPCE) close to 10% at the maximum absorption of the molecule.

Overlayer Formation as a Source of Stability in the N‐Type Photoelectrochemical Cell: The Cell

The stability of in a electrolyte is demonstrated to be due to the formation of a overlayer. Mediated hole transfer through the overlayer to solution competes with photoanodic decomposition of the electrode. The charge transfer energetics and kinetics of the overlayer are very sensitive to the supporting electrolyte cation. Variations in supporting electrolyte allow maximization of overlap between the semiconductor states and the filled levels of the surface couple. This leads to enhanced energy conversion efficiencies and minimization of electrode decomposition. For the electrode, a supporting electrolyte containing both K+ and Cs+ is found to maximize cell performance. A surface state responsible for deleterious electron transfer through the barrier is observed ∼600 mV positive of the conduction bandedge. Cells with monochromatic efficiencies in excess of 20% (488 nm) can be obtained by considering the overlayer properties.

High-efficiency organic solar cells

Organic solar cells based on merocyanine dyes have exhibited sunlight efficiencies in excess of 1% at ∼100 mW/cm2. This represents a significant improvement over previously reported values and brings such devices into the realm of practicality. The devices exhibit Voc’s as high as 1.2 V but are presently limited by field-dependent energy-dependent quantum efficiency. Though monochromatic efficiencies approaching 100% occur at high photon energies, these diminish to ∼35% at the main absorption peak in the visible. Based upon sunlight absorption, theoretical efficiencies for these devices appear high.