摘要:

To date, ThermoPhotoVoltaic (TPV) technology has been governed by Planck’s Law. To increase the photonic flux from the emitter to the receiver in a TPV system the temperature must be increased. Higher temperatures lead to materials challenges and higher parasitic system level thermal losses. In addition they make it difficult for TPV to compete in many waste heat conversion applications where the available waste heat is at temperatures less than those required for TPV. [1] Planck indicated that his law applies only if the dimensions of the system are large compared to the wavelengths of the radiation. [2] The idea that the electromagnetic energy transfer in a ThermoPhotoVoltaic (TPV) system can be increased by 5 times or more beyond Planck’s Law by placing the emitter in close proximity to the photovoltaic receiver has been proposed and studied theoretically, and has been referred to as Micron‐gap TPV (MTPV). [3] In this paper we discuss the theory, the technology, and the experimental results that obtain when the distance between the emitter and receiver surfaces is reduced to sub‐micron dimensions. The dramatic demonstration of this effect is the initial step in the development of a new class of energy conversion devices. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1539379

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In order to engineer a rare‐earth based selective emitter, having both good optical and mechanical properties, a detailed theoretical study of both the excitation and the decay processes is required at the microscopic level. In this work we present a theoretical model by which the high temperature quantum efficiencies can be evaluated on the basis of the correlation between the local symmetry of the potential around the rare earth atoms and the probability of their non‐radiative decay. The model, based on a point charge approach, provides the electric field and the crystal field parameters (CFPs) and consequently, the non radiative decay rates for a few representative configurations. The main result is that different local symmetries around, for instance, Er3+atoms may provide dramatically different non radiative decay probabilities. An experimental confirmation of the theoretical model was obtained by the analysis of a set of ceramic samples containing the same Erbium fraction and treated at different sintering temperature (in 780K –1400K range) in order to obtain different crystal phases. The radiative transition involving the orbital4I11/2→4I15/2which is expected to be quite sensitive to the different ions configurations, has been studied by means of temperature dependent photoluminescence experiments (in the range of 20K–300K) performed on samples sintered at different temperatures. The results show that the decay rate of4I11/2→4I15/2transition (not observable at room temperature) increases with increasing sintering temperature manly due to the development of a garnet configuration which strongly inhibits non radiative decay processes. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1539380

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Rugate filter technology is relatively unknown to the Solar PV‐ and the TPV community. The objective of this paper is to draw attention to Rugate filters as an enabling technology that may help to realize unprecedented conversion efficiencies in each respective field. Rugate filters are advanced optical interference filters with a continuously varied refractive index that changes periodically in the direction perpendicular to the film plane. The near noise free transmission and reflection quality of these filters, combined with their precision and the durability, promise significant improvements in the photon economy, performance and reliability of TPV devices. This paper reports the analytical modeling results for a set of Rugate filters designed for the subcells of a novel 4‐bandgap cell system with a new architecture. The purpose of this new approach is to circumvent the limitations of multi‐junction cells to achieve ultimate conversion efficiencies. The purpose of these near‐to‐perfect Rugate filters is to induce spectral splitting of concentrated solar radiation trapped in a Photovoltaic Cavity Converter by selective transmission and reflection of photons. Wideband Rugate filter designs developed for InGaP, GaAs, InGaAsP and InGaAs cells exhibit about 99&percent; average transmission over the spectral response range of the respective cells, while reflecting more than 99 &percent; of the solar photons outside their transmission band. Results of first filter deposition trials are briefly discussed in conjunction with TPV applications. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1539381

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A design study was conducted to determine the effect of various parameters on the performance of InGaAs thermophotovoltaic devices. The electrical power output density of the device, and the device efficiency were analyzed by considering different emitter temperatures and materials, various receiver band gap levels, and a range of gap spacings between emitter and receiver. The far spacing model, or spacing of magnitude much greater than the wavelength of the emitted radiation, was based on classical radiative heat transfer equations and standard photovoltaic cell equations. The close spacing model, or spacing with a magnitude on the order of magnitude of the wavelength of the emitted radiation, was based on the fluctuation‐dissipation theorem whereby the energy is transmitted by evanescent waves between the emitter and receiver. The analytical models used realistic property values for both the receiver and the emitter, and the results show the superiority of tungsten and rhenium as emitters for the far spacing case. At close spacing, silicon carbide exceeds the performance of the refractory metals down to the spacing limited by current technology. However, if spacing control technology advances and smaller gaps become feasible, rhenium emitter devices could provide a significant increase in power density, and with similar efficiencies as the far spacing case. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1539382

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Analytical expressions have been derived for the effective radiator emissivity and view factor of a given optical cavity geometry as a function of radiator emissivity and reflectance of the shield and TPV device. Using these expressions, accurate predictions of the device optical response (JSCand Qabs) have been made for two different cavity configurations (Au shield and TPV device shield). Also, the measured and calculated results show that placing a TPV device into an array of TPV devices will lower its output performance by at least 1.7&percent; (relative) compared to that measured using a Au shield. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1539383

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Results of growth, material characterization and device performance of TPV cells based on Ge, Si, InGaAs/InP, GaSb, InGaAsSb, AlGaAsSb, InAsSbP and InAs fabricated by LPE, MOCVD, MBE and diffusion methods are presented. The highest efficiencies have been obtained in TPV cells based on GaSb and InGaAs (lattice matched to InP substrate): external quantum yield as high as 90&percent; in IR‐part of photosensitivity spectrum;Voc=0.45–0.52 V;FF=0.7–0.8 at photocurrent densities of 1–5 A/cm2and efficiency of more than 10&percent; under available matched radiators. A low‐cost Zn‐diffusion technology for reproducible fabrication ofp‐n‐GaSb structures has been developed for producing the high efficiency TPV cells being used for TPV generators. Growth of epitaxial lattice‐matched AlGaAsSb wide‐bandgap windows and InGaAsSb low‐bandgap (0.5–0.6 eV) photoactive layers on GaSb substrates, as well as a fabrication of tandem TPV devices based on GaSb top cells and InGaAsSb bottom cells should allow to improve the GaSb‐based cell performance. Another approach for fabrication of the perspective TPV devices with bandgaps of 0.55–0.74 eV has been realized by growth of the lattice‐matched and mismatched InGaAs layers on InP substrates. Monolithic interconnected modules (MIMs) fabricated on semi‐insulated InP‐substrates by the MOCVD method ensure a decrease of the Joule losses and an increase of the sub‐bandgap photon reflection in the structures with a back‐surface reflector that should contribute to TPV system efficiency owing to photon recirculation. TPV cells based on InAsSbP/InAs are capable to convert radiation with wavelengths up to 2.5–3.5 &mgr;m and ensure operation with IR emitters heated to lower temperatures. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1539384

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The quaternary Sb‐based materials are attractive for use in TPV devices due to the versatility associated with being able to grow InGaAsSb and AlGaAsSb material with a wide range of band gaps lattice matched to a GaSb substrate. Photodiodes (0.60 eV) consisting of an InGaAsSb p/n junction grown on GaSb were fabricated and characterized to establish baseline electrical performance of the material. In order to fabricate monolithic interconnected modules (MIMs) from these photodiodes using a conductive GaSb substrate, an electrical isolation layer must be added between the active layers and the substrate. For this purpose, AlGaAsSb cell isolation diodes (CIDs) were developed and characterized with respect to their ability to block current in reverse bias. These structures were combined in the first MIM structures grown and fabricated from Sb‐based materials on GaSb substrates. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1539385

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The fabrication and performance of InGaAsSb thermophotovoltaic cells are described. The InGaAsSb layers, grown by organometallic vapor‐phase epitaxy in a multi‐wafer reactor, with a 0.53 eV bandgap are lattice‐matched to a GaSb substrate. Growth series with up to thirty 50 mm wafers have been done with good control of material composition and carrier transport properties. With improved materials and metallization and with a modification to the cell edges, fill factors near 70&percent; and a greater than 60&percent; peak external quantum efficiency are obtained. A two order‐of‐magnitude increase in shunt resistance with a consequent 15&percent; improvement in fill factor was achieved with the improved edge structure. Series resistance, about 20 m&OHgr;, is the remaining limitation to cell performance and is closely correlated with fill factor. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1539386

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

High‐performance GaInAsSb/AlGaAsSb/GaSb thermophotovoltaic (TPV) devices with quantum efficiency and fill factor near theoretical limits and open‐circuit voltage within about 15&percent; of the limit are reported. This paper discusses detailed studies of GaInAsSb epitaxial growth, the microstructure, and minority carrier lifetime that have led to these results. For further improvements in TPV cell performance, device structures with either a distributed Bragg reflector or a back‐surface reflector are described. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1539387

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Sarnoff Corporation has developed thermophotovoltaic (TPV) modules using either Sarnoff grown and processed InGaAsSb/GaSb TPV cells or cells fabricated by our co‐workers. The TPV module fabrication includes substrate design, fabrication and module assembly. The substrate comprises an AlN base plate and Al2O3septa. The septa separate the cells and support metal layers to electrically connect the bottom of a cell to the top of the adjacent septum. A welded gold ribbon connects the septum to the topside of the adjacent cell. The detailed structure of the substrate, as well as the module assembly process, is discussed. TPV modules of 1 cm × 1 cm area with two 1 cm × 0.5 cm cells and 2 cm × 2 cm area with eight cells are fabricated routinely. Alternative approaches to the Al2O3/AlN substrate and ribbon connection have been explored for low‐cost, large‐scale production. Silicon based substrates show promising results. KOH wet etching of silicon produces septa with straight walls having perfect 90‐degree angles at the bottom without fillets. Plated gold forming an “air bridge” to connect the cell busbar and septum has the potential to replace the welded ribbon. Packaging p‐on‐n and n‐on‐p cells alternatively can drastically reduce the complexity of the module structure by facilitating all connections on a planar surface without septa. Sarnoff module technology, when combined with Sarnoff TPV‐cell technology and spectral‐control technologies from other organizations, has led to TPV power‐conversion efficiencies exceeding 17 &percent; [1]. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1539388

出版商:AIP    

年代:1903

数据来源: AIP