GaSb Cells Research Articles

Performance analysis of near-field thermophotovoltaic system with 2D grating tungsten radiator

The effect of hyperbolic modes on near-field thermophotovoltaic (TPV) system performance is investigated by implementing a hyperbolic metamaterial (HMM) radiator. Specifically, the near-field TPV system consists of a 2D grating tungsten radiator and a gallium antimonide (GaSb) cell separated by a gap thickness varying between 100nm and 500nm. The temperatures of the radiator and the TPV cell are fixed at 2000K and 300K, respectively. The effective medium theory (EMT) is proposed to solve the near-field radiative heat transfer problem with a uniaxial anisotropic radiator. Near-field TPV performance is evaluated via maximum power output and conversion efficiency. Enhanced radiative heat transfer is observed within the spectral band where hyperbolic modes are supported by the radiator. As a result, the radiative heat flux absorbed by the cell is enhanced from broadband tunneling of evanescent waves. Furthermore, near-field TPV maximum power output and conversion efficiency are improved. The highest maximum power output and conversion efficiency are 4.28×105Wm−2 and 35%, respectively. When the gap thickness is smaller than 300nm, the effect of hyperbolic modes is strong, and radiative losses affect the conversion efficiency as radiative flux is enhanced both below and above the cell bandgap. For gap thicknesses larger than 300nm, the effect of hyperbolic modes is weak and the conversion efficiency is mostly affected by the spatial distribution of radiative flux absorbed in the cell. In this study, radiative heat flux enhancement and the improvement of near-field TPV performance are attributed to hyperbolic modes supported by the radiator. These findings will further contribute to the design of near-field TPV experimental systems outperforming their far-field counterparts.

Simple Rectangular Gratings as a Near-Field \u201cAnti-Reflection\u201d Pattern for GaSb TPV Cells

We show theoretically that 2D rectangular gratings on the surface of GaSb can serve as an “anti-reflection” pattern for nano-gap thermophotovoltaic (TPV) devices, which significantly enhances near-field radiative flux from the emitter to a GaSb cell, thus improving output power and conversion efficiency. The system in this study is a 200-nm gap TPV power generation system with a planar infrared plasmonic emitter and GaSb cell. Rigorous coupled-wave analysis is used to calculate the spectral near-field radiative flux involving periodic structures. The simulation shows that when coupled with a near-infrared plasmonic bulk emitter, adding gratings on the GaSb cell surface results in strong spectral enhancement above the cell’s bandgap and suppression for low-energy photon transmission, an effect that cannot be fully predicted by the effective medium theory. The resultant peak spectral heat flux is 2.8 times as high as the case without surface structures and the radiative transfer efficiency increased to 24.8% from the original 14.5% with the emitter temperature at 1800 K. The influence of the grating’s geometry parameters on the enhancement and peak frequency is further discussed with rigorous calculation of the spatial distribution of thermal radiative transfer that provided insight into the physical mechanism.

The Theoretical Performance of GaInAsSb and GaSb Cells Versus IR Emitter Temperature in Thermophotovoltaic Systems

GaInAsSb cells may show better performance than GaSb cells in low-temperature thermophotovoltaic systems due to their lower bandgap energies. In this paper, numerical simulation is used to evaluate GaInAsSb and GaSb cells with similar structures under different radiation temperatures. We find that GaInAsSb cells with n-type emitters show slightly higher output power densities compared with those for GaSb cells with n-type emitters below 1500 K given-blackbody radiation, but the power density of the GaSb cells will surpass the former’s above this temperature point. Furthermore, over the temperature range of $1200\sim 2000$ K, the efficiencies of GaSb cells with n-emitters are $1.31\sim 2.32$ times higher than those of GaInAsSb cells with n-emitters if filters with 10% subbandgap losses are used. Several parameters that affect the GaInAsSb cell were analyzed, such as doping profiles, thicknesses of GaInAsSb epitaxial layer and surface recombination velocity. The n-on-p junctions, i.e., n-type emitters vs p-type emitters are better for GaInAsSb cell fabrication, which is similar to that for the GaSb cell.

Performance assessment of thermophotovoltaic application in steel industry

The potential for using Thermophotovoltaic (TPV) generators as an alternative for recovering energy losses in steel production industry is assessed. A mathematical model for the assessment of the performance of TPV application in the iron and steel industry has been developed. In order to support the mathematical model, a sample TPV apparatus in laboratory scale based on an IR emitter has been designed and assembled. The key modeling parameters of TPV generator include: the open circuit voltage, the short circuit current density and fill factor of the TPV cell. These parameters have been considered in the model as functions of several variables such as: the emitter (hot steel slab) temperature, the cell temperature, the distance between the cells and emitter, the spectral response and the cell energy gap. The External Quantum Efficiency (EQE) as an important indicator of the cell׳s spectral response is included in the model. Moreover, the variation of the emitter temperature has been considered. Several tests have been carried out for different values of the cell-emitter gap. It has been found that when the GaSb cells are used for energy recovery, a minimum temperature of 873°C is required. The upper limit of the emitter temperature is usually determined in steel production process associated with hot rolling process which has a temperature around 1250°C. Finally, the total efficiency of the system was obtained to 4.12%, when GaSb cell with temperature of 27°C and slab emitters with temperature of 1257°C are used. The results of the simulation of the model in a casting process at the Mobarakeh Steel Complex have shown a potential of energy recovery of 26.987MJ per year.

Performance Improvement of the GaSb Thermophotovoltaic Cells With n-Type Emitters

GaSb cells are commonly fabricated using Zn diffusion into n-GaSb, and in this paper they have been designed inversely using Te diffusion into unintentionally p-doped GaSb. Numerical simulation is used to analyze the cell performance. We found that a GaSb cell with n-type emitters showed a significantly higher output power density compared with that of the cell with p-type emitters under 1500 K-blackbody radiation. The performance improvement is owing to the good matching of the diffusion length of minority carriers with the depth of their moving regions. Several parameters that affect the cell performance were analyzed, such as doping depth, substrate thickness, and surface recombination velocity. The cell performance was evaluated under low temperature radiations and found to have huge potentials for the use in low-temperature thermophotovoltaic systems.

Thin-film 'Thermal Well' Emitters and Absorbers for High-Efficiency Thermophotovoltaics.

A new approach is introduced to significantly improve the performance of thermophotovoltaic (TPV) systems using low-dimensional thermal emitters and photovoltaic (PV) cells. By reducing the thickness of both the emitter and the PV cell, strong spectral selectivity in thermal emission and absorption can be achieved by confining photons in trapped waveguide modes inside the thin-films that act as thermal analogs to quantum wells. Simultaneously, photo-excited carriers travel shorter distances across the thin-films reducing bulk recombination losses resulting in a lower saturation current in the PV cell. We predict a TPV efficiency enhancement with near-field coupling between the thermal emitter and the PV cell up to 38.7% using a thin-film germanium (Ge) emitter at 1000 K and an ultra-thin gallium antimonide (GaSb) cell supported by perfect back reflectors separated by 100 nm. Even in the far-field limit, the efficiency is predicted to reach 31.5%, which is over an order of magnitude higher than the Shockley Queisser limit of 1.6% for a bulk GaSb cell and a blackbody emitter at 1000 K. The proposed design approach does not require nanoscale patterning of the emitter and PV cell surfaces, but instead offers a simple low-cost solution to improve the performance of thermophotovoltaic systems.

High-efficiency solar-thermophotovoltaic system equipped with a monolithic planar selective absorber/emitter

We demonstrate a high-efficiency solar-thermophotovoltaic system (STPV) using a monolithic, planar, and spectrally selective absorber/emitter. A complete STPV system using gallium antimonide (GaSb) cells was designed and fabricated to conduct power generation tests. To produce a high-efficiency STPV, it is important to match the thermal radiation spectrum with the sensitive region of the GaSb cells. Therefore, to reach high temperatures with low incident power, a planar absorber/emitter is incorporated for controlling the thermal radiation spectrum. This multilayer coating consists of thin-film tungsten sandwiched by yttria-stabilized zirconia. The system efficiency is estimated to be 16% when accounting for the optical properties of the fabricated absorber/emitter. Power generation tests using a high-concentration solar simulator show that the absorber/emitter temperature peaks at 1640 K with an incident power density of 45 W/cm2, which can be easily obtained by low-cost optics such as Fresnel lenses. The conversion efficiency became 23%, exceeding the Shockley–Queisser limit for GaSb, with a bandgap of 0.67 eV. Furthermore, a total system efficiency of 8% was obtained with the view factor between the emitter and the cell assumed to be 1.

Preparation and performance evaluation of Er2O3 coating-type selective emitter

An Er2O3 coating-type selective emitter for themophotovoltaic application was prepared by plasma spray technology. The test results show that plasma spray technology could be used to prepare the Er2O3 coating-type selective emitter with good stability at 1400°C. Based on the measurements of the high temperature normal spectral emissivity and the spectral hemispherical emissivity of the samples at room temperature, the influence of the coating thickness was discussed, and the selective emission performance of the sample was evaluated using radiative efficiency as the criterion. The results demonstrate that the emission of substrate could not be neglected unless the coating thickness would be larger than the penetration depth, which is around 100 μm. The selective emission peak of the Er2O3 coating occurs at 1550 nm, matching well with the GaSb cells. However, the radiative efficiency is not larger than that of the SiC emitter, because the non-convertible emission of 1.725–5 μm accounts for a large proportion of the total radiation power, especially at high temperature. Effective suppression of this band emission is essential to the improvement of the radiation efficiency of the emitter.

A novel zinc diffusion process for the fabrication of high-performance GaSb thermophotovoltaic cells

This paper reports a novel zinc diffusion method for forming emitters in GaSb thermophotovoltaic cells. A closed quartz-tube diffusion system using Zn–Ga alloys as the diffusion source was designed to realize p-type doping in N-GaSb wafers. The surface diffusion region showing a high concentration of zinc was suppressed by this diffusion method, and the GaSb cells fabricated using this method showed good quantum efficiency in the near-infrared bands. Compared to that of the conventional pseudo-closed-box diffusion method, the controllability of the etch-back process after front-side metallization is significantly improved, and the cost of the cell fabrication is reduced because no protective gas is required during the diffusion process.

The design and numerical analysis of tandem thermophotovoltaic cells

In this paper, numerical analysis of GaSb =(Eg = 0.72 eV)/Ga0.84In0.16As0.14Sb0.86 (Eg = 0.53 eV) tandem thermophotovoltaic (TPV) cells is carried out by using Silvaco/Atlas software. In the tandem cells, a GaSb p-n homojunction is used for the top cell and a GaInAsSb p-n homojunction for the bottom cell. A heavily doped GaSb tunnel junction connects the two sub-cells together. The simulations are carried out at a radiator temperature of 2000 K and a cell temperature of 300 K. The radiation photons are injected from the top of the tandem cells. Key properties of the single- and dual-junction TPV cells, including I–V characteristic, maximum output power (Pmax), open-circuit voltage (Voc), short-circuit current (Isc), etc. are presented. The effects of the sub-cell thickness and carrier concentration on the key properties of tandem cells are investigated. A comparison of the dual-TPV cells with GaSb and GaInAsSb single junction cells shows that the Pmax of tandem cells is almost twice as great as that of the single-junction cells.

Thermophotovoltaic Generation of Electricity through Evanescent Wave Effect Using GaSb Cells

Thermophotovoltaic Generation of Electricity through Evanescent Wave Effect Using GaSb Cells

Ceramic IR Emitter with Spectral Match to GaSb PV Cells for TPV

ABSTRACTA high temperature ceramic selective emitter for thermophotovoltaic (TPV) electric generators is described with a spectral match to GaSb IR cells. While solar cells generate electricity quietly and are lightweight, traditional solar cells are used with sunlight and only generate electricity during the day. Workers at JX Crystals invented the GaSb IR cell as a booster cell to demonstrate a solar cell conversion efficiency of 35%. JX Crystals now makes these IR cells. In TPV, these cells can potentially be used with flame heated ceramic emitters to generate electricity quietly day and night. One of the most important requirements for TPV is a good spectral match between the ceramic IR emitted and the IR PV cells. The first problem is to find, demonstrate, and integrate a doped ceramic IR emitter with a spectral match to these GaSb cells. Recently, nickel oxide and cobalt oxide doped MgO-based ceramics have been shown experimentally and theoretically to have spectral selectivity but no attempts have been made to integrate these ceramic IR emitters into a fully operational TPV generator. Herein, we review the history of TPV and note that a key to future progress will be the integration of an appropriate ceramic emitter with cells and a burner to demonstrate an operational TPV generator. Integrating TPV into a residential boiler is discussed as a potential future large volume commercial market.

Electricity generation from thermal irradiation governed by GaSb active layer

Abstract Electricity generation from thermal irradiation governed by GaSb diode has been systematically investigated in its normal and inverted configuration. It is demonstrated here that there is a critical base doping, 3 × 1017 cm−3, for the normal structure, and the superior output performance of p+/n structure with low base-doping would completely be switched to the n+/p structure when base doping larger than this critical one. Moreover, a spectrum-independent optimal doping concentration, Na = 1.5 × 1017 cm−3, is also observed for n+/p structure, and no doping-dependent thickness compensation between emitter and base layer can be observed for the inverted structure. To save the material consumption and device cost, the reasonable active layer can be constructed by 100–200 nm emitter and 5–7 μm base, offering the useful guideline to fabricate the GaSb cell on the economical but lattice-mismatched hetero-substrate.

Thermophotovoltaic power conversion from a heat-recirculating micro-emitter

Power generation using a novel configuration of a 1–10W micro-thermophotovoltaic (micro-TPV) device is studied experimentally. A micro-emitter as a thermal heat source is a simple cylinder with an annular-type shield that applies a heat-recirculation concept and an expanded exhaust outlet that facilitates ignition, which provides stable burning in the small confinement and uniform distribution of temperature along the wall. The micro-emitter is surrounded by a chamber with cooling fins, the inner wall of which has an installation of gallium antimonide photovoltaic cells (PVCs). The performance of the micro-TPV device is most favorable at reduced length of the cooling fins unless the temperature on the PVCs is higher than the operating limit temperature for the GaSb cells. The relative position of the micro-emitter to the PVCs also affects the performance of the micro-TPV device. These observations imply that the net amount of heat irradiation onto the PVCs is more dominant than the PVC temperature in determining the TPV performance. Under optimized operating conditions, the micro-TPV device produces 2.4 Wwith an overall efficiency of 2.1%, indicating that the efficiency up to the PVC surface is 21% at least if a PVC efficiency of 10% at most is assumed.

D103 エバネッセント波を利用したGaSb熱光起電力発電(OS1 マイクロエネルギー変換)

D103 エバネッセント波を利用したGaSb熱光起電力発電(OS1 マイクロエネルギー変換)

Experimental analysis of cell output performance for a TPV system

The experimental U– I characteristics of a single GaSb cell, a single Si cell and their modules in a TPV system using a SiC radiator were investigated. The influence of the radiator temperature and the radiator–cell distance on the output performances of a single cell and its module was analyzed. The results demonstrate that increasing the radiator temperature or decreasing the radiator–cell distance both lead to the increasing the short-circuit current density and the output power density, but the open-circuit voltage decreases because of the rise of the cell temperature. The maximum output power densities of a single GaSb cell and the corresponding module are 0.26 and 0.28 W/cm 2, respectively, which are approximately 4.3 and 6.0 times that of a single Si cell and its module for a combustion power of 4.2 kW and a radiator–cell distance of 1.1 cm. Furthermore, a mathematical physical model was constructed to analyze the influence of the cell temperature on the output performance of the cells. For a given radiator temperature and radiator–cell distance, the theoretical results indicate that the output power density decreases with cell temperature because of attenuation of the open-circuit voltage.

Gas-fired thermophotovoltaic generator based on metallic emitters and GaSb cells

A prototype compact TPV generator with a propane burner (pressure 2 bar) and a metallic netted emitter has been developed and tested. A photovoltaic generator unit with 24 (1 × 1 cm2) GaSb cells has been fabricated. The fabrication technology of photovoltaic cells has been optimized. It is shown that the data obtained can be used to select the starting bulk material for fabrication of photovoltaic cells with similar output parameters. It has been experimentally demonstrated that, to achieve maximum efficiency, it is necessary, in addition to using photovoltaic cells with similar characteristics, to provide identical conditions of their operation (temperature, illuminance).

Evaluation of thermal radiation dependent performance of GaSb thermophotovoltaic cell based on an analytical absorption coefficient model

Applying the model dielectric function method, we have expressed the absorption coefficient of GaSb analytically at room temperature relating to the contribution of various critical points of its electronic band structure. The calculated absorption spectrum shows good agreement with the reported experimental data obtained by spectral ellipsometry on nominally undoped sample. Based on this analytical absorption spectrum, we have qualitatively evaluated the response of active absorbing layer structure and its photoelectric conversion properties of GaSb thermophotovoltaic device on the perturbation of external thermal radiation induced by the varying radiator temperature or emissivity. Our calculation has demonstrated that desirable thickness to achieve the maximum conversion efficiency should be decreased with the increment of radiator temperature and the performance degradation brought by any structure deviation from its optimal one would be stronger meanwhile. For the popular radiator temperature, no more than 1500 K in a real solar thermophotovoltaic system, and typical doping profile in GaSb cell, a reasonable absorbing layer structure parameter should be controlled within 100–300 nm for the emitter while 3000–5000 nm for the base.

SOLAR ENERGY DELIVERING GREENHOUSE WITH AN INTEGRATED NIR FILTER

The scope of this investigation is the design and development of a new type of greenhouse with an integrated filter for rejecting near infrared radiation (NIR) and a solar energy delivery system. Cooled greenhouses are an important issue to cope with the combination of high global radiation and high outdoor temperatures. As a first measure, the spectral selective cover material, which prevents the entrance of NIR radiation, is investigated. The special spectral selective properties of these materials have to block up to 50% of the solar energy outside the greenhouse, which will reduce the needed cooling capacity. The second measure is the integration of a solar energy system. When the NIR reflecting coating is designed as a parabolic or circular shaped reflector integrated in the greenhouse, the reflected solar energy of a PhotoVoltaic (PV) cell in the focus point delivers electric energy. With a ray tracing computer program the geometry of the reflector was optimally designed with respect to the maximum power level. The PV cells mounted in the focal point require cooling due to the high heat load of the concentrated radiation (concentration factor of 30-40). The properties of different materials, Ge, GaSb, CIS and Si cells were investigated to find the optimal cell for this application. All parts are integrated in a greenhouse structure with a size of about 100m2.

Investigation of one-dimensional Si/SiO2 hotonic crystals for thermophotovoltaic filter

The spectral control is widely incorporated with the thermophotovoltaic (TPV) technology to improve the optical-electric conversion efficiency of the whole system. In order to match with GaSb photovoltaic cell, an 8-layer one-dimensional photonic crystals (PC) filter structure was designed as quarter-wave periodic structure by selecting silicon (Si) and silicon dioxide (SiO2) as candidate materials. The multilayer Si/SiO2 structure was developed for the matching filter to simultaneously realize the optimal matching with the spectral distribution of the high temperature emitter and the quantum efficiency of GaSb cell. The physical vapor deposition (PVD) method was used to fabricate the optical filter and the normal incidence optical property of the filter was measured within the spectral range from 0.7 to 3.3 μm. These experimental data were used to predict the spectral control performance in a TPV system. Finally, temperature performance experiments were carried out to establish its withstanding performance in high temperature environment.