Thermophotovoltaic System Research Articles

Theoretical insights into narrow bandgap CuFeS2 chalcopyrite for thermophotovoltaic applications

CuFeS2 chalcopyrite compound with a parochial direct band-gap of 0.55 eV could be a potential candidate for thermophotovoltaic (TPV) cells. In this paper, a theoretical analysis has been performed on CuFeS2 compound utilizing density functional theory (DFT) to reveal its suitability in TPV applications. The configuration of electrons and their distribution of energy levels indicate the semiconducting nature of the compound. Then, CuFeS2 based single p-n junction TPV cell has been designed and simulated based on the transport equation of the semiconductor device model. The CuFeS2 thermophotovoltaic shows a 5% efficiency achieved with a VOC of 0.261 V, JSC of 10.90 A/cm2, and a fill factor (FF) of 69.49% at a black body temperature (TBB) of 1625 K. The findings can provide valuable insights for producing cost-effective CuFeS2 thermophotovoltaic systems.

Analysis of a photon-recycling optical cavity in a cylindrical thermophotovoltaic system considering thermal load in cells

Thermophotovoltaics (TPVs) hold immense promise for efficient heat-to-electricity conversion via photons, particularly considering advancements in photon-recycling techniques. We investigated the design of an optical cavity for a TPV system in which the emitters were radially surrounded by cells, with the goal of applying the photon-recycling effect in practical TPV systems. Employing ray-trace simulations, we explored the influence of various parameters on TPV system performance. The optimal optical cavity was designed with the same area of emitter and cell under a constant cell temperature. Incorporating the thermal behavior of the cell into the simulation model yielded significantly different system efficiencies, emphasizing the importance of temperature considerations. Despite some discrepancies, experimental validations and theoretical analyses described the thermal behavior of gallium antimonide cells. Optimization under different conditions indicated a potential for the system efficiency of these cells to exceed 40 %. To further enhance the performance of TPVs, future efforts should focus on increasing the cell’s out-of-band reflectance, improving cooling, and optimizing area ratios for specific cell reflectance and heat dissipation situations. This study provides essential insights into the comprehensive design of a TPV system with an optical cavity by combining photon-recycling and the temperature dependence of the cell.

A high-temperature solar selective absorber based on one-dimensional multilayer nanostructures

Selective absorbers play a crucial role in harvesting solar energy and realizing effective solar-thermal energy conversion in concentrated solar power systems and thermophotovoltaic systems. This study focuses on obtaining a high-temperature solar selective absorber which can well balance its thermal performance as well as structural complexity. Based on this, a selective absorber with simple one-dimensional multilayer nanostructures is designed to adapt to the high-temperature operation environments. The obtained absorber exhibits a total solar absorptance of 0.9504 to the AM1.5 solar radiation. Taking into account the infrared radiation loss, the solar-thermal efficiency of the absorber is found to be 91.2% under 1000 suns at 1273 K, and the total emittance is 0.1504 at the corresponding temperature. The absorber shows high insensitivity to both incident polarization angles and wide-angle incidence. Analysis of impedance and electromagnetic field distribution indicates that the selective absorption performance of the absorber is attributed to its impedance matching properties, resulting from the coupling effect of surface plasmon polaritons and magnetic polaritons.

Highly efficient molybdenum nanostructures for solar thermophotovoltaic systems: One-step fabrication of absorber and design of selective emitter

Efficient solar energy harvesting materials or structures have become a topic of great interest in response to the ever-increasing energy demand. Refractory transition metals have been found to exhibit attractive properties in broadband absorptance, making them highly effective in solar thermophotovoltaic (STPV) systems that aim to surpass the Shockley-Queisser limit. Typically, broadband absorbers are made from hybrid materials or complex geometrical structures, which require multi-step fabrication technologies. In this study, we successfully developed a highly efficient broadband absorber based on molybdenum (Mo) nanosheets using a one-step physical vapor deposition process. The nanosheets result in the high absorber efficiencies of 96.1 % for blackbody radiation (BBR) at 5778 K and of 96.4 % for air mass (AM) 1.5 spectrum, and are insensitive to polarization and incident angle. After annealing at 1650 K for 24 h, the Mo nanosheets absorber demonstrates outstanding thermal stability without compromising the efficiency of the STPV system. To complete the STPV system, a selective narrowband Mo-based gratings emitter was further designed with a high emissivity of 96 % at a wavelength of 2.17 μm, resulting in a high PV cell efficiency of 41.8 % around 1723 K. Through a series of theoretical calculations, the proposed STPV system can achieve an overall conversion efficiency of 40.2 % by a trade-off between the structure temperature and the sun concentration. Furthermore, an efficiency of 35.5 % can be achieved at a low temperature of 1073 K with a low solar concentration of 500 suns.The results provide tremendous opportunities for widespread applications of high-performance STPV systems.

Experimental performance comparison of 0.72 eV-GaSb and 0.59 eV-InGaAs thermophotovoltaic cells under different radiation temperatures

The field of Thermophotovoltaic (TPV) has recently exhibited highly promising characteristics. The performance of thermophotovoltaic (TPV) cells with 0.72 eV-GaSb and 0.59 eV-InGaAs varies at different radiation temperatures, as demonstrated in this experimental study. The research evaluates and compares the TPV cell performance under radiation temperatures ranging from 800 to 1200 °C, and analyses the impact of temperature on critical parameters. The maximum efficiencies achieved for GaSb and InGaAs cells were 23.10% and 28.91%, respectively, under tungsten radiation spectrum at a temperature of 1200 °C. This comprehensive analysis provides valuable insights into optimizing TPV systems for efficient thermal-to-electrical energy conversion using GaSb and InGaAs cells.

Exploring combustion characteristics of a novel micro combustor with a fan swirler for thermophotovoltaic system

The combustion and thermal characteristics of non-premixed methane (CH4)–air flames in a swirl micro combustor are numerically investigated for potential use in a thermophotovoltaic (TPV) system. Swirling flows associated with methane–air combustion are simulated using a Reynolds stress model and detailed chemistry of GRI-Mech 3.0. The optimal condition for improved emission and combustion performance is established by taking into account six blade angles and three fuel-lean equivalence ratios, to consider among other geometric features of the fan swirler and operating conditions.The reactive swirling flows in a micro combustor with a fan swirler are modified by altering the blade angle (θb). For θb = 5°, 10°, and 15°, the swirl micro combustor with a two-vortex structure exhibits a significant enhancement of the fuel–air mixing and thermal performance compared to no-swirl combustor. As θb increases, inner vortices close to the fuel stream and outer vortices near the combustor wall behind the fan blades are developed according to the interaction of swirling flows and recirculating flows due to the blockage effect of the fan blades. For θb = 15°, the strong interaction between two vortex regions maximizes combustion efficiency. The combustion efficiency is highest at θb = 15° and lowest at θb = 75°. For three fuel-lean conditions of θb = 15°, the flame zone is enlarged towards the combustion chamber wall, resulting in a high and uniform wall temperature. The resulting radiant emitter efficiencies for a TPV system are increased by 28.3 %–35.1 % compared to that of the no-swirling micro combustor. The results indicate that the fan swirler has recirculation flows for the best emitter and combustion efficiency unlike vane-type swirlers.

Ultra-broadband and wide-angle plasmonic light absorber based on all-dielectric gallium arsenide (GaAs) metasurface in visible and near-infrared region

High-performance and cost-effective broadband light absorbers are crucial for various optical applications, including solar energy harvesting, thermophotovoltaic systems, and integrated photoelectric devices. In this study, an ultra-broadband and wide-angle plasmonic light absorber (PLA) based on an all-dielectric gallium arsenide (GaAs) metasurface in the visible and near-infrared regions is proposed and numerically investigated. The unit-cell of the proposed PLA is consisted of all-dielectric GaAs cylinder resonator (CR) adhered on an ultra-thin GaAs spacer layer backed with a tungsten (W) substrate. Numerical simulation results show that the absorption peak of the proposed PLA is up to 99.85 %, 99.9 % and 99.98 % at 0.452 μm, 0.712 μm and 1.596 μm, respectively. In addition, the ultra-broadband strong absorption of over 90 % also can be achieved from 0.39 μm to 2.09 μm with a relative bandwidth of 137.1 %. The ultrabroadband strong absorption of the proposed PLA is further demonstrated by the equivalent circuit model (ECM), which displays excellent agreement with the results of the full-wave numerical simulation performed using the finite element method (FEM). The simulated electromagnetic (EM) field distributions reveal that the ultra-broadband strong absorption of the designed PLA is mainly from the excited propagating surface plasmon (PSP), located surface plasmon (LSP), cavity resonance modes combined with coupling effect between adjacent CRs. The proposed PLA is also polarization-insensitive and wide incident angles for both transverse electric (TE) and transverse magnetic (TM) modes. The absorption properties of the designed PLA can be adjusted by varying geometric parameters of the unit-cell. The PLA achieves a remarkable short-circuit current density of over 64.75569 mA/cm2 and exhibits nearly perfect solar energy trapping due to the effective coupling of multiple resonances, resulting in enhanced photovoltaic performance. Thus, the proposed PLA can be potential application in the photodetectors, thermal imaging, and solar energy harvesting devices.

Improving the Efficiency of Solar Thermophotovoltaic Energy Conversion System

Solar energy can be directly or indirectly converted into other types of energy such as heat and electricity. However, several obstacles cause the insignificant use of such energy, including scientific and technical weaknesses in conversion due to lack of knowledge and field experiences, variable energy amount due to atmospheric and seasonal changes and radiation direction, as well as a very wide distribution scale. A comprehensive review of methods to improve the performance of solar thermophotovoltaic energy conversion systems in order to enhance efficiency is one of the most important aspects of innovation in this study. Computer modeling of thermal systems has various benefits, such as adjusting the cost of prototype construction, optimizing system components, estimating the amount of output energy, predicting system temperature changes, and other low-priority cases. This study also presents the results of the execution of the relevant files by engineering equation solver (EES) software ©1992-2003 S.A. Klein offers Commercial Version 6.883-3D (09/01/03). The results are represented in the form of tables and comparative plots. The investigations carried out include thermodynamic, exergetic, and economic parameters.

Thermophotovoltaic emitter design with a hyper-heuristic custom optimizer enabled by deep learning surrogates

Micro/nanostructures hold promise for use as emitters to boost the efficiency of thermophotovoltaic (TPV) systems. For example, periodic gratings may alter the spectrum of irradiation on the photovoltaic cell to better match the spectral response of the cell. Photons with energies slightly higher than the bandgap of the semiconductor are the most desired as they generate electron-hole pairs with minimal thermalization losses. This prompts the use of gratings as selective emitters, and the choice of grating geometry has been an active research topic. Even for a one-dimensional (1D) grating, millions of possible geometries exist, and each grating requires computationally intensive full-wave simulation, e.g., the rigorous coupled-wave analysis (RCWA), to calculate the spectral, directional emissivity. Since optimization algorithm performance is problem-dependent, in this work, a hyper-heuristic search enabled by a fully connected neural network surrogate of the native RCWA is employed to select an algorithm for a specific grating design problem. A comparison with existing untuned algorithms for an ideal emitter problem demonstrates that the hyper-heuristically generated algorithm yields superior performance. This algorithm is then employed for the optimization of the emitter for a full TPV system comprising a heated 1D tungsten binary grating paired with a 300 K InGaSb cell. The system is optimized for maximum power or efficiency at 2000 K and 1500 K, respectively, and the grating properties for the optimized cases are analyzed.

On the Performance of Solar Thermophotovoltaics (STPVs) and Wavelength-Selective Thermophotovoltaics (TPVs): Case Study of a High-Rise Residential Building in a Hot and Semi-Arid Climate

Utilizing integrated solar systems and renewable energy sources has the potential to not only decrease the CO2 emissions of buildings but also provide access to more affordable energy alternatives compared to fossil fuels, especially considering the recent rise in prices. Nevertheless, many designers and project decision makers are hesitant to embrace solar technologies due to the uncertainty surrounding the cost–benefit balance. This paper presents a case study of the design process, highlighting the energy-saving and cost–benefit aspects of a solar façade featuring solar thermophotovoltaics (STPVs) and wavelength-selective thermophotovoltaics (TPVs) in a high-rise residential building situated in the semi-arid climate of Tehran, Iran. The simulation methodology consists of EnergyPlus Engines in Rhino, along with the Ladybug and Honeybee plugins throughout the solar façade design process. The solar façade incorporating STPV yielded energy savings of 25 kWh per square meter, marking a 34% reduction compared to a standard façade. In contrast, the TPV demonstrated energy savings of 35 kWh per square meter, indicating a 48% decrease in energy consumption compared to a regular façade. This research indicates that, particularly in semi-arid climatic conditions, TPV systems exhibit a superior performance when integrated into the façades of high-rise structures; yet, due to the low electricity prices in the region, neither STPVs nor TPVs are financially viable. The study contributes to raising awareness, fostering technological innovations, influencing policy discussions, and promoting the adoption of sustainable practices in the field of energy and architecture.

Visible-to-near-infrared asymmetric transmission through a cross grating

Broadband asymmetric transmission (BAT) structures are in high demand for optical devices, computing, and thermal management. While achieving asymmetric transmission in a broad waveband remains challenging. In this work, we propose a simple cross grating made of SiO2 and silver (Ag) and demonstrate its ability to asymmetrically transmit visible-to-near-infrared radiation. Results indicate that the proposed grating achieves a BAT performance in the range of 0.4 – 1.5 μm, with a max forward transmissivity of 0.95 which is larger than the backward one which is always smaller than 0.45. The proposed structure in this work paves a high-performance candidate for achieving BAT in the visible-to-near-infrared wavelength ranges and, thus, has promising applications in thermal management devices such as thermophotovoltaic systems and smart windows.

Performance of new designed meta-material absorbers/emitters reshaping solar spectrum to double-narrowband emissive spectrum for STPV power generation

Solar thermophotovoltaic system can reshape the solar spectrum and improve the conversion efficiency of photovoltaic. In this study, the characteristics of ideal selective absorber for AM0 and AM1.5 solar spectra are compared, and the principles are summarized to design a metamaterial absorber for different spectra. The absorption efficiency can reach more than 80 % at the high temperature of 1700 K. This study innovatively proposes a STPV system that matching a double-narrowband (DNB) emitter with Si/InGaAsSb tandem cells. The theoretical efficiency of STPV with a DNB emitter is about 4 % higher than that with a wide-band (WB) emitter by analyzing thermodynamic model. Accordingly, a metamaterial DNB emitter is designed. The results show that the DNB metamaterial selective emitter designed in this study can achieve a TPV efficiency of near 50 %. The concentrating ratio and temperature have an inverse effect on the absorption efficiency and TPV efficiency. The optimized STPV system efficiencies for AM0 and AM1.5 are 37.29 % and 37.20 % under typical condition, respectively, which are a great improvement compared to the solar PV cell. The proposed metamaterial absorber and DNB emitter have great application potential in power generation for both space and ground conditions.

An elliptical nanoantenna array plasmonic metasurface for efficient solar energy harvesting.

Plasmonic metasurfaces with subwavelength nanoantenna arrays have attracted much attention for their ability to control and manage optical properties. Solar absorbers are potential candidates for effectively converting photons into heat and electricity. This study introduces a novel ultrathin metasurface solar absorber employing elliptical-shaped nanoantenna arrays. We theoretically and numerically demonstrate a near-perfect broadband absorber with over 90% absorption efficiency in a wide range of wavelengths of 300-2500 nm, using finite element (FEM) and finite-difference time-domain (FDTD) methods. The proposed nanostructure configuration enhances light absorption by exciting localized surface plasmon resonances (LSPRs) between elliptical-shaped nanoantenna gaps at many wavelengths, maintaining stability at wide incident angles and insensitivity to light polarization. Compared to other state-of-the-art absorbers with a thickness of less than 300 nm, the designed nanostructure with 260 nm thickness achieves over 90% optical absorption across a broad range of wavelengths of 300-1116 nm in air (or vacuum) environments and performs effectively under water conditions for solar energy harvesting in a range of wavelengths of 300-1436 nm, and therefore can serve as a solar evaporator. Combining refractory plasmonic titanium nitride (TiN) and semiconductor gallium nitride (GaN) nanostructures holds great potential for efficient optoelectronic and photocatalytic applications, especially in harsh and high-temperature environments like thermophotovoltaic systems. The TiN-based metasurface absorber, with its ultrathin nanostructure and suitable spectral absorption in ultraviolet-visible-infrared spectra, offers scalability and cost-effectiveness. The findings in this work will deepen our understanding of LSPRs and pave a novel path for efficient solar energy conversion.

Design of efficient thermophotovoltaic system based on meta-material narrow-band emitter for space power supply

Photovoltaic technology has been widely used in spacecraft power supply, but its efficiency is difficult to be greatly improved by Shockley-Queisser limitation. The thermophotovoltaic technology can convert solar radiation energy or high temperature combustion energy into radiation energy with reshaped spectrum for direct photovoltaic power generation. In this study, a meta-material structure composed of metal tantalum, Ta, and dielectric SiO2 is innovatively proposed for shaping narrowband radiation. The results show that the optimized spectral emittance peak of narrowband emitters reaches 0.9998. Narrowband emitter has advantages at high temperatures above 1000 K. The thermophotovoltaic efficiency of InGaAsSb cell and tandem Si/InGaAsSb cells can reach more than 41.67% and 46.26%, respectively. It is significantly higher than published thermophotovoltaic system with broadband emitter. This study demonstrates the notable advantages and potential of narrowband emitter for spectrum reshaping, which provides an important reference for future spacecraft power supply as well as space solar power generation.

A tungsten-based metamaterial emitter for solar thermophotovoltaic systems.

Solar thermophotovoltaic systems are capable of showing efficient photoelectric conversion and are expected to surpass the Shockley-Queisser limit, owing to the spectrum-selective functionality of metamaterial selective emitters. Generally, metamaterial emitters are manufactured from multifarious materials, which also makes their manufacturing process complicated. Here, we propose a tungsten-only emitter composed of two rectangular bars with different widths and heights arranged in a cruciform structure, featuring a rectangular cavity at the top. Results from the simulations reveal that the emissivity of the metamaterial emitter exceeds 90% at the wavelength of 950-1590 nm and drops below 20% for wavelengths exceeding 2025 nm, which can effectively match GaSb photovoltaic cells. The outstanding emission performance is attributed to the coupling effect of surface plasmon resonance, cavity resonance and guided mode resonance, as evidenced by the analysis of electric and magnetic fields. We also explored the radiation spectrum in the 500-2500 K temperature range and found that it performed best at 1400 K. It is concluded that the emission performance is slightly affected by structural parameters and angles. This study presents a meaningful exploration of efficient solar utilization.

Screening and optimization of metal-insulator-metal selective emitter in thermophotovoltaic system

In thermophotovoltaic (TPV) systems, it is crucial that the selective emitters can tailor emission spectrum to match the bandgap of photovoltaic (PV) cells and largely enhance the system efficiency. In this work, a metamaterial emitter based on the metal-insulator-metal (MIM) structure is proposed to obtain the high energy conversion efficiencies. The geometric parameters of MIM emitter have been investigated to obtain an excellent radiation spectrum of emitter composed of W and HfO2. The excellent emission performance of MIM emitter is attributed to the excitation of surface plasmon polariton (SPP) and cavity resonance, and the structure of MIM emitter is insensitive for different polarization modes. The 21 material combinations of MIM emitters have been screened to obtain the optimal emitter matching GaSb and InGaAsSb cells. This work identifies the crucial role of structure and materials into the emitter of a TPV system. In the evaluation of MIM emitter and TPV System, when the operating temperature of emitter increases from 1400[Formula: see text]K to 2000[Formula: see text]K, the system efficiency of optimal W/HfO2/W MIM emitter increases from 20.26% to 30.41%, while the output electric power increases from 3.59[Formula: see text]kW/m2 to 42.48[Formula: see text]kW/m2. The phenomenon indicates that the MIM emitter with the optimal material combinations and geometric parameters can significantly improve the matching degree with GaSb and InGaAsSb cells. Our results will be helpful to expand the optimization scope of metamaterial emitters in TPV systems.

Efficiency boost and financial analysis of the thermophotovoltaic power system by photonic potential

A hybrid thermophotovoltaic system for thermal-to-electrical energy conversion is a solid-state technique that exclusively utilizes infrared light. However, it faces an upper limit on its conversion efficiency. In this study, its performance is enhanced by integrating concentrated solar energy and a thermal battery. A surface-to-surface radiative analysis in COMSOL is conducted to determine the thermal-to-electrical conversion efficiency. In addition to photon recycling, facilitated by spectral filters, the cells' junction is externally biased to impart a positive photonic chemical potential. This enhances the spectral intensity due to a higher apparent temperature and an increased entropy content. Consequently, it raises the thermal-to-electric energy conversion efficiency to 49% in a real-world scenario and up to 56% in an ideal case. Arbitrage is introduced into this power plant by incorporating an electric grid heater in the system, which bypasses solar heating. It stores electric energy during off-peak hours and provides it during on-peak hours. In this research, financial analysis is carried out using GAMS, and an estimated arbitrage of up to $920/kW-year is achieved from the electricity grid in Pennsylvania, New Jersey, and Maryland (PJM). The thermal battery in the system is also compared with other energy storage devices, proving it to be advantageous compared to Li-Ion and lead-acid batteries, which exhibit higher unit energy storage and conversion costs.

High-Selectivity Planar Thermal Emitter with a Stable Temperature over 1400 K for a Thermophotovoltaic System.

A selective thermal emitter with superior thermal stability and perfect selective thermal emission in specific bands can facilitate the lifting of the thermophotovoltaic (TPV) energy conversion efficiency in TPV systems. Scalable planar selective thermal emitters with superior spectral selectivity and robust high-temperature stability are desired to meet the requirements of large-scale deployments of TPV systems. However, stably reradiating the available thermal photons at above 1273 K remains a significant challenge for selective thermal emitters. In this work, we demonstrated a high-selectivity planar thermal emitter based on the composite ceramic of ZrC and Al2O3. The prepared selective thermal emitter provides an emissivity of around 90% above the photon energy (0.6 eV) at 1423 K, a strong emission suppression effect below 0.6 eV, and superior thermal stability up to at least 1423 K. Therefore, the overall spectral efficiency can reach around 53%. Coupled with an InGaAs PV cell, the TPV system based on the selective thermal emitter demonstrates a predicted heat-to-electricity power conversion efficiency of 29.78% at 1423 K due to the matched spectral response of the emitter with the PV cell. Our work opens a new way forward for TPV systems based on planar selective thermal emitters.

Improved thermophotovoltaic system performance with a novel metamaterial thermal emitter combined with a passive radiative cooling approach

Thermophotovoltaic (TPV) energy conversion systems have gained great interest in recent years as they can directly convert thermal energy into electricity using photovoltaic (PV) cells. The increase of the radiative power and the power conversion efficiency in TPV systems is mainly due to two key factors. The first one deals with the nature of the selective emitter. A new high temperature selective emitter should be designed to have a high emissivity (absorptivity) above the bandgap energy (Eg) and a low emissivity below Eg of the PV cells. The second key factor is related to the cooling mechanism of the PV cell as the conversion efficiency of the latter degrades with increasing temperature. In this work, we first propose and investigate a new efficient metamaterial thermal emitter, to reach a desired emissivity in the wavelength range 0.8−1.72μm. Secondly, to minimize the operating temperature of the TPV system, a passive radiative cooling approach is suggested in which an efficient double-layer coating deposited on the substrate of PV cells is elaborated. It has a high emissivity in the atmospheric transparency windows 8−13μm and low absorptivity in the solar spectrum 0.3−8μm. We show that the high-temperature metamaterial design can achieve high emissivity, over 0.97 in the wavelength range, 0.8−1.72μm, while reducing the sub-band loss of the PV cells. At 1400K, we demonstrate that adding the proposed cooling design to the substrate of a GaSb PV cell panel with an area ratio between the passive radiative cooler and the PV cell panel of γ=20, can improve the efficiency of the latter by 2% and drop its operating temperature by 44K.

Core–shell structure selective emitter doped with rare earth elements for solar thermophotovoltaic system

Aiming at the low utilization of radiation photons in the solar thermophotovoltaic system, a rare earth core–shell (REC) structure selective thermal emitter is designed to achieve selective emission. The 3D symmetrical opal core–shell structure and rare earth elements play an important role in the selective emission characteristic of the REC emitter. The opal core–shell structure of the REC emitter is optimized by finite difference time domain simulation and numerical calculation, and the optimal size is determined. The REC emitter can adjust the characteristic peak of rare earth elements to produce a narrow–band radiation peak with an emissivity approaching 1 at a wavelength just before the cutoff wavelength, and maintain low emissivity in the long and short–wave bands. The conversion efficiency of the solar thermophotovoltaic system based on the REC emitter and InGaAs cell is 17.29 % at 1400 K, and the power density can reach 428.3 mW/cm2. The mechanism of the selective emission characteristic of the REC emitter is revealed, and its emissivity is insensitive to polarization and incidence angle. The REC emitter further improves the selective emission characteristic and makes the radiation spectrum better match the thermophotovoltaic cell. The power density and conversion efficiency of the solar thermophotovoltaic system are increased by improving the utilization of the thermophotovoltaic cell to the radiation photon.