WO2023101973A1

WO2023101973A1 - Bandpass assembly for thermo-photovoltaic devices

Info

Publication number: WO2023101973A1
Application number: PCT/US2022/051264
Authority: WO
Inventors: Jon William STEWART; John REIFENBERG; Kegan James BAIRD
Original assignee: Sierra Nevada Corporation
Priority date: 2021-11-30
Filing date: 2022-11-29
Publication date: 2023-06-08

Abstract

Methods, devices, and systems are described for a bandpass assembly configured to filter light from an emitter in a TPV system. The apparatus includes a substrate configured to pass light from a first side to a second side in which the second side is approximately parallel to the first side. The apparatus includes a first multilayered structure coupled to the first side of the substrate. The first multilayered structure has at least two layers comprising at least one of a dielectric multilayer, a semiconductor multilayer, a metallic-dielectric multilayer, a semiconductor-dielectric multilayer, a metallic-semiconductor multilayer, a metallic- semiconductor-dielectric multilayer. The apparatus includes a second multilayered structure coupled to the second side of the substrate. The second multilayered structure has at least two layers including at least one of a dielectric multilayer, a semiconductor multilayer, a metallic- dielectric multilayer, a semiconductor-dielectric multilayer, a metallic-semiconductor multilayer, a metallic-semiconductor-dielectric multilayer.

Description

BANDPASS ASSEMBLY FOR THERMO-PHOTOVOLTAIC DEVICES

CROSS-REFERENCE TO APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63/284,262 entitled “BANDPASS ASSEMBLY FOR THERMO-PHOTOVOLTAIC DEVICES” and filed on November 30, 2021, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates generally to generating energy, and more particularly, to a bandpass assembly for thermo-photovoltaic devices.

BACKGROUND

[0003] Thermo-photovoltaic (TPV) power generation systems use the photovoltaic (PV) effect to convert heat into thermal radiation and electrical power. TPV systems comprise an emitter configured to deliver heat and thermal radiation, and a PV cell configured to receive the thermal radiation from the heated emitter. The PV cell converts the thermal radiation or thermally-emitted photons into electrical power by utilizing a semiconductor with an appropriate bandgap. The thermally-emitted photons of higher energy than the bandgap excite electron-hole pairs in the semiconductor to generate electricity for an external electrical system. Emitters of TPV systems radiate a greater range of photon energies than what can be efficiently absorbed and converted to electricity by the PV cell.

SUMMARY

[0004] The present disclosure relates generally to the fields of generating energy, including systems and methods useful for a bandpass assembly for filtering light from an emitter in a TPV system.

[0005] In one aspect, disclosed herein are apparatuses for a bandpass assembly configured to filter light from an emitter in a TPV system. The apparatus includes a substrate configured to pass light from a first side to a second side in which the second side is approximately parallel to the first side. The apparatus includes a first multilayered structure coupled to the first side of the substrate. The first multilayered structure has at least two layers comprising at least one of a dielectric multilayer, a semiconductor multilayer, a metallic- dielectric multilayer, a semiconductor-dielectric multilayer, a metallic-semiconductor multilayer, a metallic-semiconductor-dielectric multilayer. The apparatus includes a second multilayered structure coupled to the second side of the substrate. The second multilayered structure has at least two layers including at least one of a dielectric multilayer, a semiconductor multilayer, a metallic-dielectric multilayer, a semiconductor-dielectric multilayer, a metallic- semiconductor multilayer, a metallic-semiconductor-dielectric multilayer. At least a portion of the light is configured to pass light from the first multilayered structure to the second multilayered structure. The apparatus is configured to pass light having a wavelength above a first wavelength cutoff, and the apparatus is configured to pass light having a wavelength below a second wavelength cutoff.

[0006] In some variations, the second side of the substrate has a small angular offset up to 5 degrees relative to the first side of the substrate and wherein the substrate further comprises at least one of silicon, glass, ZnSe, Sapphire, and GaAs. Further, the substrate includes a plurality of substrates with each substrate of the plurality of substrates having a different structure, and wherein the glass may include at least one of silicon dioxide, borofloat, UV grade glass, and IR grade glass. Additionally, the at least two layers of the first multilayered structure includes at least one of a highly-doped semiconductor layer and a transparent conducting oxide layer.

[0007] In some variations, the at least two layers of the second multilayered structure includes at least one of a highly-doped semiconductor layer and a transparent conducting oxide layer. Further, the first multilayered structure is a shortpass filter and wherein the second multilayered structure is at least one of a bandpass filter and a longpass filter. Additionally, the first multilayered structure is a bandpass filter and wherein the second multilayered structure is at least one of a shortpass filter, a bandpass filter, a longpass filter, and an antireflection coating.

[0008] In some variations, the first multilayered structure is a longpass filter and wherein the second multilayered structure is at least one of a shortpass filter and a bandpass filter. Further, the first multilayered structure is an antireflection coating and wherein the second multilayered structure is a bandpass filter. Additionally, the apparatus is configured to be interposed between a light emitter and a photovoltaic cell. In some variations, the first wavelength cutoff is greater than or equal to 0.7 pm and the second wavelength cutoff is less than or equal to 10 pm and the difference between the second wavelength cutoff and the first wavelength cutoff is less than or equal to 1.5 pm.

[0009] In another aspect, disclosed herein are systems for a bandpass assembly configured to filter light from an emitter in a TPV system. The apparatus includes a substrate configured to pass light from a first side to a second side in which the second side is approximately parallel to the first side. The apparatus includes a first multilayered structure coupled to the first side of the substrate. The first multilayered structure faces a source of light and has at least two layers comprising at least one of a dielectric multilayer, a semiconductor multilayer, a metallic-dielectric multilayer, a semiconductor-dielectric multilayer, a metallic- semiconductor multilayer, a metallic-semiconductor-dielectric multilayer. The apparatus includes a second multilayered structure coupled to the second side of the substrate. The second multilayered structure faces a photovoltaic cell and has at least two layers including at least one of a dielectric multilayer, a semiconductor multilayer, a metallic-dielectric multilayer, a semiconductor-dielectric multilayer, a metallic-semiconductor multilayer, a metallic- semiconductor-dielectric multilayer. At least a portion of the light is configured to pass light from the first multilayered structure to the second multilayered structure. The apparatus is configured to pass light having a wavelength above a first wavelength cutoff, and the apparatus is configured to pass light having a wavelength below a second wavelength cutoff.

[0010] In some variations, the second side of the substrate has a small angular offset up to 5 degrees relative to the first side of the substrate, wherein the substrate includes a plurality of substrates with each substrate of the plurality of substrates having a different structure, and wherein the substrate further comprises at least one of silicon, glass, ZnSe, Sapphire, and GaAs. Further, the first wavelength cutoff is greater than or equal to 0.7 pm and the second wavelength cutoff is less than or equal to 10 pm and the difference between the second wavelength cutoff and the first wavelength cutoff is less than or equal to 1.5 pm. Additionally, wherein the at least two layers of the first multilayered structure includes at least one of a highly-doped semiconductor layer and a transparent conducting oxide layer.

[0011] In some variations, the at least two layers of the second multilayered structure includes at least one of a highly-doped semiconductor layer and a transparent conducting oxide layer. Further, the first multilayered structure is a shortpass filter and wherein the second multilayered structure is at least one of a bandpass filter and a longpass filter. Additionally, the first multilayered structure is a bandpass filter and wherein the second multilayered structure is at least one of a shortpass filter, a bandpass filter, a longpass filter, and an antireflection coating.

[0012] In some variations, the first multilayered structure is a longpass filter and wherein the second multilayered structure is at least one of a shortpass filter and a bandpass filter. Further, the first multilayered structure is an antireflection coating and wherein the second multilayered structure is a bandpass filter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The embodiments herein may be better understood by referring to the following description in conjunction with the accompanying drawings in which like reference numerals indicate identically or functionally similar elements, of which:

[0014] FIG. 1 depicts a bandpass assembly interposed between an emitter and a PV cell in a TPV system;

[0015] FIG. 2 depicts a bandpass assembly having a substrate with a first multilayered structure on one side and a second multilayered structure coupled to the second side;

[0016] FIG. 3 depicts a bandpass assembly configured to transmit light between a first wavelength cutoff and a second wavelength cutoff and configured to reflect or absorb light below the first wavelength cutoff and light above the second wavelength cutoff;

[0017] FIG. 4 depicts a table of desirable combinations for a bandpass assembly selected from a shortpass filter, a bandpass filter, a longpass filter, and an anti reflection coating;

[0018] FIG. 5 depicts a bandpass assembly coupled to a front side of a PV cell and interposed between an emitter and the PV cell in a TPV system;

[0019] FIG. 6 depicts a bandpass assembly interposed between an emitter and a PV cell in a TPV system in which the PV cell is located in a recess and situated to only receive a portion of the thermal radiation from the emitter based on the TPV system structure;

[0020] FIG. 7 depicts a bandpass assembly interposed between an emitter and a PV cell in a TPV system including reflective surfaces between the emitter and the PV cell; and [0021] FIG. 8 depicts a table representative of the efficiency of the TPV system based on various input components.

DETAILED DESCRIPTION

[0022] The methods, systems, and apparatuses described herein are for a bandpass assembly for a TPV system. In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols generally identify similar components, unless context dictates otherwise. The illustrative alternatives described in the detailed description, drawings, and claims are not meant to be limiting. Other alternatives may be used and other changes may be made without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this application.

[0023] Distributed electrical generation is becoming increasingly important. Common challenges for conventional generators and distributed electricity generation include efficiency, noise, and maintenance demands. TPV generators are uniquely positioned to address many of these demands due to their scalable efficiency, few moving parts, and near silent operation. Additionally, TPV systems may be relatively fuel agnostic, permitting hydrogen and other carbon-free fuels to be used. In the relevant power regime for TPV systems (~10s of kW and lower), TPV systems can potentially outperform any technology in its class with respect to gravimetric/volumetric energy densities including lithium-ion batteries. TPV systems are commonly incorporated with different high-grade heat sources (with their own ewergy-heat efficiencies) including but not limited to concentrated solar power, radioisotope heaters, electrical heaters, or chemical combustors.

[0024] But one drawback of TPV systems is the emitter tends to radiate more thermal energy than what can be efficiently absorbed and converted to electricity by the PV cell. This causes various efficiency problems including the potential overheating of the PV cell. Additionally, PV cells have a myriad of specifications to effectively absorb incident photons and convert them into electrical energy. These specifications may lead to a mismatch between the emitted photon energies and the energies that can be efficiently converted by the PV cell. For example, spectral losses arise from a mismatch between the PV cell’s bandgap energy and the energy of the thermally-emitted photons. Photons with energy less than the PV bandgap cannot be converted into electrical energy due to the photovoltaic effect. Photons with energy greater than the PV bandgap may also lose energy due to band edge relaxation and cause overheating of the PV cell. The quantum efficiency of the PV cell also influences spectral losses. A high quantum efficiency means that most or all photons incident to the PV cell generate a charge carrier that may be extracted externally from the PV cell. The quantum efficiency of the PV cell will vary with the photon energy incident on the cell, where lower quantum efficiency may be caused by non-ideal absorption and carrier recombination. Spectral losses arise when the energy of the thermally-emitted photons aligns with a lower quantum efficiency in the PV cell meaning that the generated charge carriers are not extracted from the PV cell.

[0025] The concepts described herein improve the TPV system efficiencies with a novel bandpass assembly for TPV systems. The bandpass assembly may be independently tuned to the heat flux/temperature relationship between the emitter and the PV cell. Unlike previous solutions, the bandpass assembly here may enable a flexible temperature and heat flux design across a range of heat sources (e.g., flame, hot radiant surfaces, conductive surfaces) and heat transfer conditions. Additionally, the bandpass assembly may have a configurable thermal impedance that may be easily designed to alter the relationship between the emitter temperature and net energy flux to the PV cell. Additionally, the bandpass filter may be simultaneously optimized for the heat source or cooling load and independently designed for the spectrum and power incident requirements of the PV cell.

[0026] The bandpass assembly may control the spectrum incident on the PV cell by passing a range of wavelengths of light and reflecting or absorbing light outside the wavelength range. That is, the bandpass assembly may filter and/or reflect light outside of the wavelength range required by the PV cell. Additionally, the bandpass assembly may recycle photons by reflecting them back at the emitter to be absorbed. Unlike previous bandpass filter solutions, the bandpass assembly described herein may be configured to have independent control over the magnitude, shape, and angle dependence of the transmittance/reflectance windows of the radiated energy from the emitter. Unlike the nano- and micro-structured metallic bandpass filters that inherently limit the design space for TPV systems, the bandpass assembly described herein has a flexible design and adaptability for a variety of heat sources.

[0027] The bandpass assembly may include a reflective bandpass filter. The reflective bandpass filter may enable only a select range of wavelengths to transmit to the PV cell, and all wavelengths outside this range may be reflected back to the emitter. In some embodiments, the reflective bandpass optical assembly may include an optical system that reduces the angle of incidence for the thermal radiation as well as mitigates losses from thermal radiation with high angles of incidence. The reflective bandpass optical assembly may include a reflective or scattering baffle around the extremities of the optical system to mitigate losses from thermal radiation or thermal radiation with high angles of incidence. The reflective bandpass optical assembly may include a concentrating optical system to focus the emitted light onto a smaller PV cell. The reflective bandpass optical assembly may be a stand-alone filter or it may be situated on the front surface of the PV cell. The optical system may include a lens that reduces the angle of incidence for the thermal radiation.

[0028] FIG. 1 depicts a bandpass assembly 125 interposed between an emitter 110 and a PV cell 115 in a TPV system 100. The TPV system 100 may be configured to convert the thermal radiation emitted from an emitter 110 into electrical energy via a PV cell 115. TPV power systems require no moving parts, which allows them to be inherently quiet and reduces maintenance requirements relative to engines in the same design space. To increase the thermodynamic efficiency of the TPV system 100, a bandpass assembly 125 may be interposed between the emitter 110 and the PV cell 115.

[0029] The emitter 110, PV cell 115, and the bandpass assembly 125 may be placed into a housing 105. The bandpass assembly 125 may be interposed between emitter 110 and the PV cell 115 in the housing 105. The housing 105 may enclose the PV cell 115 and the bandpass assembly 125. In some embodiments, the PV cell 115 may be positioned in the bottom portion of the housing 105 and configured to only receive light emitted from the emitter 110. In some embodiments, the bandpass assembly 125 may be situated within the housing 105 such that only light from the emitter 110 within a specific wavelength range may pass through the bandpass filter. Vacuum 130 may exist between the PV cell 115 and the bandpass assembly 125 and between the emitter 110 and the bandpass assembly 125. Vacuum 130 may be created by the housing 105 being airtight to the external environment. Insulation 150 may be interposed along the edges and crevices of the housing 105 to make the housing 105 airtight or to reduce parasitic thermal and optical losses. Additionally, the insulation 150 may include a porous or semi-porous material to make the TPV system 100 more efficient.

[0030] The emitter 110 may be a broadband thermal emitter 110. The emitter 110 may be configured to have an operating temperature of at least 1250K. The emitter 110 may be a gray body emitter 110, a black body emitter 110, or a spectrally-selective emitter 110. The spectrally-selective emitter 110 may be configured to radiate energy at the bandgap determined by the PV cell 115. For example, the emitter 110 may be configured to emit a majority of thermal radiation within a wavelength range between 0.7 pm and 10 pm. In some embodiments, the emitter 110 may emit a minimal amount of thermal radiation outside the wavelength range between 0.7 pm and 10 pm. In some embodiments, the emitter 110 may radiate more thermal energy than what can be efficiently absorbed at the PV cell 115.

[0031] The PV cell 115 may be configured to absorb the thermal radiation from the emitter 110 and convert the thermal radiation to electricity. The PV cell 115 may have a myriad of specifications to effectively absorb incident photons from the emitter 110 and convert them into electrical energy. These specifications of the emitter 110 should match the specifications of the PV cell 115. For example, spectral losses may be minimized as the thermally-emitted photons from the emitter 110 match the PV cells bandgap energy. Otherwise, thermally-emitted photons with energy less than the PV cell 115 bandgap cannot be converted into electrical energy due to the photovoltaic effect and thermally-emitted photons with energy greater than the bandgap of the PV cell 115 may also lose energy due to band edge relaxation and cause overheating of the PV cell 115. In another example, the conversion efficiency of the PV cell 115 may be maximized when the emitter 110 matches the highest quantum efficiency of the PV cell 115. A high quantum efficiency results from most or all photons incident to the PV cell 115 generating an electron that is extracted externally from the PV cell 115.

[0032] The bandgap assembly may be configured to control the spectrum incident on the PV cell 115 by passing a range of wavelengths of light and reflecting or absorbing light outside the wavelength range. That is, the bandpass assembly 125 may filter and/or reflect light outside of the wavelength range required by the PV cell 115. Additionally, the bandpass assembly 125 may recycle photons by reflecting them back at the emitter 110 to be absorbed. The bandpass assembly 125 may transmit a select band of wavelengths to the PV cell 115 with an independently designable wavelength range and transmission magnitude.

[0033] FIG. 2 depicts a bandpass assembly 125 having a substrate 210 with a first multilayered structure 220 on one side and a second multilayered structure 230 coupled to the second side. The multilayered structures may be configured to reflect or filter out certain wavelengths of light thereby filtering light outside of the energy bandgap of the PV cell 115. The bandpass assembly 125 may be spaced by vacuum 130 between the emitter 110 and the PV cell 115. In some embodiments, the substrate may be a plurality of substrates where each substrate of the plurality of substrates includes a separate structure.

[0034] A substrate 210 may have a disk shape or a cylindrical shape and may be rigid or flexible. In some embodiments, the substrate 210 may be a wafer. In some embodiments, the substrate 210 may be a flexible sheet or roll. The substrate 210 may be configured to deposit or adhere the first multilayered structure to one side and mount the second multilayered structure 230 to the opposing side. The substrate 210 may be configured to pass light from a first side to a second side where the second side is approximately parallel to the first side. In some embodiments, the substrate 210 may be configured such that the second side has a small angular offset up to 5 degrees relative to the first side. That is, a portion of the light is configured to pass through the substrate 210 from the first multilayered structure 220 to the second multilayered structure. The substrate 210 may be transparent to enable light to pass from the first side to the second side. In some embodiments, the first side may face the emitter 110 and the second side may face the PV cell 115. The substrate 210 may be made from at least one of silicon, glass, ZnSe, Sapphire, GaAs, or other low-cost substrates. In embodiments in which the substrate 210 includes glass, the glass may include at least one of silicon dioxide, borofloat, UV grade glass, and IR grade glass. In some embodiments, the substrate 210 having a curved or cylindrical shape may be manufactured by applying a roll-to-roll processing technique to a flexible substrate.

[0035] The first multilayered structure 220 may be coupled to the first side of the substrate 210. In some embodiments, the first multilayered structure 220 may be deposited directly onto the substrate 210 using a physical vapor deposition technique. The first multilayered structure 220 may have at least two layers. The at least two layers may comprise at least one of a dielectric multilayer, a semiconductor multilayer, a metallic-dielectric multilayer, a semiconductor-dielectric multilayer, a metallic-semiconductor multilayer, a metallic-semiconductor-dielectric multilayer. The at least two layers of the first multilayered structure 220 may include at least one of a highly-doped semiconductor layer and/or a transparent conducting oxide layer. The at least two layers may include alternating materials. For example, a metal layer and a dielectric layer may be arranged in an alternating pattern. In another example, a metallic-semiconductor layer may be arranged in an alternating pattern with a dielectric layer. In yet another example, a highly-doped semiconductor or transparent conducting oxide layer may be included into an alternating multilayer structure. [0036] A second multilayered structure 230 may be coupled to the second side of the substrate 210. In some embodiments, the first multilayered structure 220 may be deposited directly onto the substrate 210 using a physical vapor deposition technique. The second multilayered structure 230 may have at least two layers. The at least two layers may comprise at least one of a dielectric multilayer, a semiconductor multilayer, a metallic-dielectric multilayer, a semiconductor-dielectric multilayer, a metallic-semiconductor multilayer, a metallic-semiconductor-dielectric multilayer. The at least two layers of the second multilayered structure 230 may include at least one of a highly-doped semiconductor layer and/or a transparent conducting oxide layer. The at least two layers may include alternating materials. For example, a metal layer and a dielectric layer may be arranged in an alternating pattern. In another example, a metallic-semiconductor layer may be arranged in an alternating pattern with a dielectric layer. In yet another example, a highly-doped semiconductor or transparent conducting oxide layer may be included into an alternating multilayer structure.

[0037] The bandpass assembly 125 may include a reflective bandpass filter. The reflective bandpass filter may enable only a select range of wavelengths to transmit to the PV cell 115 and all other wavelengths are reflected back to the emitter 110. In some embodiments, the reflective bandpass optical assembly may include an optical system that reduces the angle of incidence for the thermal radiation as well as mitigates losses from thermal radiation with high angles of incidence. The reflective bandpass optical assembly may include a reflective or scattering baffle around the extremities of the optical system to mitigate losses from thermal radiation or thermal radiation with high angles of incidence. The reflective bandpass optical assembly may include a concentrating optical system to focus the emitted light onto a smaller PV cell. The reflective bandpass optical assembly may be a stand-alone filter or the reflective bandpass optical assembly may be situated on the front surface of the PV cell 115. The optical system may include a lens that reduces the angle of incidence for the thermal radiation.

[0038] FIG. 3 depicts a bandpass assembly 125 configured to transmit light between a first wavelength cutoff and a second wavelength cutoff and configured to reflect or absorb light below the first wavelength cutoff and light above the second wavelength cutoff. The bandpass assembly 125 may maximize reflection of wavelengths between 0.7 and 10 microns back to the emitter 110. The select wavelength range may be based on the efficiency and power density requirements of the PV cell 115 or the emitter 110, the heat source temperature, the heat flux available to the emitter 110, and other factors. In some embodiments, the narrower the select band of wavelengths, the higher the parasitic losses are relative to the transmitted power. The parasitic losses may alter where the peak efficiency of the TPV system 100 will occur relative to the energy transmitted in the select band of wavelengths.

[0039] The bandpass assembly 125 may be configured to pass light having a wavelength above a first wavelength cutoff. The apparatus may be configured to pass light having a wavelength below a second wavelength cutoff. In some embodiments, the first wavelength cutoff is greater than or equal to 0.7 pm and the second wavelength cutoff is less than or equal to 10 pm. In some embodiments, the bandpass assembly 125 may be enabled to only permit light to pass through a transmission window of wavelengths. The transmission window may be less than or equal to 1.5 pm. Put another way, the transmission window may be the difference between the second wavelength cutoff and the first wavelength cutoff, which measures less than or equal to 1.5 pm. The bandpass assembly 125 may reflect or absorb light outside of this transmission window.

[0040] FIG. 4 depicts a table of desirable combinations for a bandpass assembly 125 selected from a shortpass filter, a bandpass filter, a longpass filter, and an antireflection coating. The table may be organized by desirable combinations of first multilayered structures 220 and second multilayered structures 230 that will create bandpass filter. A shortpass filter may be an optical structure configured to reflect or attenuate wavelengths above a threshold value and transmit wavelengths below the threshold value. A longpass filter may be an optical structure configured to reflect or attenuate wavelengths below a threshold value and transmit wavelengths above the threshold value. An antireflection coating may be configured to be applied to a surface of an optical structure to reduce reflection of transmittable light.

[0041] In some embodiments, the first multilayered structure 220 may be a shortpass filter and the second multilayered structure 230 may be at least one of a bandpass filter and a longpass filter. In some embodiments, the first multilayered structure 220 may be a bandpass filter and the second multilayered structure 230 may be at least one of a shortpass filter, a bandpass filter, a longpass filter, and an antireflection coating. In some embodiments, the first multilayered structure 220 may be a longpass filter and the second multilayered structure 230 may be at least one of a shortpass filter and a bandpass filter. In some embodiments, the first multilayered structure 220 may be an antireflection coating and wherein the second multilayered structure 230 may be a bandpass filter. [0042] In some embodiments, the second multilayered structure 230 may be a shortpass filter and the first multilayered structure 220 may be at least one of a bandpass filter and a longpass filter. In some embodiments, the second multilayered structure 230 may be a bandpass filter and the first multilayered structure 220 may be at least one of a shortpass filter, a bandpass filter, a longpass filter, and an antireflection coating. In some embodiments, the second multilayered structure 230 may be a longpass filter and the first multilayered structure 220 may be at least one of a shortpass filter and a bandpass filter. In some embodiments, the second multilayered structure 230 may be an antireflection coating and wherein the first multilayered structure 220 may be a bandpass filter.

[0043] FIG. 5 depicts a bandpass assembly 125 coupled to a front side of a PV cell 115 and interposed between an emitter 110 and the PV cell 115 in a TPV system 100. The bandpass assembly 125 may be a reflective bandpass optical assembly. The reflective bandpass optical assembly may be a stand-alone filter or reflective bandpass optical assembly may be situated on the front surface of the PV cell 115.

[0044] As shown in FIG. 5, the bandpass assembly 125 may be coupled to a side of the PV cell 115. The bandpass assembly 125 may be coupled to the side of the PV cell 115 facing the emitter 110. In some embodiments, the reflective bandpass optical assembly may include a longpass filter and a back reflector. The longpass filter may be situated between the emitter 110 and the PV cell 115 and the back reflector may be situated at the PV cell 115. The back reflector may be equivalent to a shortpass filter configured to reflect sub-bandgap radiation back to the emitter 110 and absorb photons with higher energies than the PV cell bandgap. The longpass filter and the back reflector may be designed to create an effective bandpass filter by tuning the cut-on wavelength of the longpass filter relative to the bandgap wavelength. In some embodiments, the reflective bandpass optical assembly may include an optical system that reduces the angle of incidence for the thermal radiation as well as mitigates losses from thermal radiation with high angles of incidence. The reflective bandpass optical assembly may include a reflective or scattering baffle around the extremities of the optical system to mitigate losses from thermal radiation or thermal radiation with high angles of incidence. The reflective bandpass optical assembly may include a concentrating optical system to focus the emitted light onto a smaller PV cell. The reflective bandpass optical assembly may be a stand-alone filter or reflective bandpass optical assembly may be situated on the front surface of the PV cell 115. The optical system may include a lens that reduces the angle of incidence for the thermal radiation.

[0045] In some embodiments, the reflective bandpass optical assembly may include a reflective metallic grating to angularly separate the select band of wavelengths to be transmitted to the PV cell 115 and the other wavelengths to be reflected back to the emitter 110. The reflective bandpass optical assembly may include a mirror to reflect the angularly separated wavelengths to the PV cell 115 after they have been transmitted through the reflective bandpass optical assembly. In some embodiments, the reflective bandpass optical assembly may include an optical assembly that reduces the angle of incidence for the thermal radiation as well as mitigates losses from thermal radiation with high angles of incidence. The reflective bandpass optical assembly may include a reflective or scattering baffle around the extremities of the optical system to mitigate losses from thermal radiation or thermal radiation with high angles of incidence. The reflective bandpass optical assembly may include a concentrating optical system to focus the emitted light onto a smaller PV cell. The reflective bandpass optical assembly may be a stand-alone filter or it may be situated on the front surface of the PV cell 115. In some variations, a reflector may be added to receive the reflected wavelengths from the mirror and reflect the sub-bandgap wavelengths to the emitter 110.

[0046] In some embodiments, the reflective bandpass optical assembly may include a reflective metallic grating to angularly separate the select band of wavelengths to be transmitted to the PV cell 115 and to be reflected back to the emitter 110. The reflective bandpass optical assembly may include a mirror to reflect the angularly separated wavelengths to the PV cell 115 after they have been transmitted to through the reflective bandpass optical assembly. In some embodiments, the reflective bandpass optical assembly may include an optical assembly that reduces the angle of incidence for the thermal radiation as well as mitigates losses from thermal radiation with high angles of incidence. The reflective bandpass optical assembly may include a reflective or scattering baffle around the extremities of the optical system to mitigate losses from thermal radiation or thermal radiation with high angles of incidence. The reflective bandpass optical assembly may include a concentrating optical system to focus the emitted light onto a smaller PV cell. The reflective bandpass optical assembly may be a stand-alone filter or it may be situated on the front surface of the PV cell 115. In some variations, a reflector may be added to receive the reflected wavelengths from the mirror and reflect the sub-bandgap wavelengths to the emitter 110. [0047] The housing 105 may include a reflective side surface 145. The reflective side surface 145 may be situated at a first side and a second side of the recess in the housing 105. The reflective side surface 145 may extend from the bottom of the recess to the top of the recess. The reflective side surface 145 may maximize the likelihood that the transmitted light from the bandpass assembly 125 is absorbed by the PV cell 115. In some embodiments, the reflective side surface 145 may extend through the vacuum 130 between the emitter 110 and the PV cell 115.

[0048] FIG. 6 depicts a bandpass assembly 125 interposed between an emitter 110 and a PV cell 115 in a TPV system 100 in which the PV cell 115 is located in a recess and situated to only receive a portion of the thermal radiation from the emitter 110 based on the TPV system 100 structure.

[0049] The emitter 110, PV cell 115, and the bandpass assembly 125 may be placed into a housing 105 including a recess. The bandpass assembly 125 may be interposed between emitter 110 and the PV cell 115 in the recess of the housing 105. The housing 105 may envelop the PV cell 115 and the bandpass assembly 125. The bandpass assembly 125 may include a concentrating optical system to focus the emitted light onto a smaller PV cell. In some embodiments, the PV cell 115 may be positioned in the bottom portion of the recess of the housing 105 and configured to only receive a portion of light emitted from the emitter 110. In some embodiments, the bandpass assembly 125 may be situated within the recess of the housing 105 such that only a portion of the light from the emitter 110 within a specific wavelength range may pass through the bandpass filter. Vacuum 130 may exist between the PV cell 115 and the bandpass assembly 125 and between the emitter 110 and the bandpass assembly 125. Vacuum 130 may be created by the housing 105 being airtight to the external environment. Insulation 150 may be interposed along the edges and crevices of the housing 105 to make the housing 105 airtight or to reduce parasitic thermal and optical losses. Additionally, the insulation 150 may include a porous or semi-porous material to make the TPV system 100 more efficient.

[0050] The housing 105 may include a reflective side surface 145. The reflective side surface 145 may be situated at a first side and a second side of the recess in the housing 105. The reflective side surface 145 may extend from the bottom of the recess to the top of the recess. The reflective side surface 145 may maximize the likelihood that the transmitted light from the bandpass assembly 125 is absorbed by the PV cell 115. In some embodiments, the reflective side surface 145 may extend through the vacuum 130 between the emitter 110 and the PV cell 115.

[0051] FIG. 7 depicts a bandpass assembly 125 interposed between an emitter 110 and a PV cell 115 in a TPV system 100 including reflective surfaces 155 between the emitter 110 and the PV cell 115. The emitter 110, PV cell 115, and the bandpass assembly 125 may be placed into a housing 105 including a recess with reflective surfaces 155. The bandpass assembly 125 may be interposed between emitter 110 and the PV cell 115 in the recess of the housing 105. The housing 105 may envelop the PV cell 115 and the bandpass assembly 125. The bandpass assembly 125 may include a concentrating optical system to focus the emitted light onto a smaller PV cell. In some embodiments, the PV cell 115 may be positioned in the bottom portion of the recess of the housing 105 and configured to only receive a portion of light emitted from the emitter 110. This portion of light may be maximized by the reflective surfaces 155 located at the sides of the bandpass assembly 125 and the PV cell 115. The reflective surfaces 155 may maximize the likelihood that the transmitted light from the bandpass assembly 125 is absorbed by the PV cell 115. In some embodiments, the bandpass assembly 125 may be situated within the recess of the housing 105 such that only a portion of the light from the emitter 110 within a specific wavelength range may pass through the bandpass filter. Vacuum 130 may exist between the PV cell 115 and the bandpass assembly 125 and between the emitter 110 and the bandpass assembly 125. Vacuum 130 may be created by the housing 105 being airtight to the external environment. Insulation 150 may be interposed along the edges and crevices of the housing 105 to make the housing 105 airtight or to reduce parasitic thermal and optical losses. Additionally, the insulation 150 may include a porous or semi-porous material to make the TPV system 100 more efficient.

[0052] The housing 105 may include a reflective side surface 145. The reflective side surface 145 may be situated at a first side and a second side of the recess in the housing 105. The reflective side surface 145 may extend from the bottom of the recess to the top of the recess. The reflective side surface 145 may maximize the likelihood that the transmitted light from the bandpass assembly 125 is absorbed by the PV cell 115. In some embodiments, the reflective side surface 145 may extend through the vacuum 130 between the emitter 110 and the PV cell 115.

[0053] FIG. 8 depicts a table representative of the efficiency of the TPV system 100 based on various input components. The table may demonstrate that the heat transfer coefficient and the heat-electricity efficiency may be controlled nearly independently through design of the filter’s bandwidth (lines 1-5) and transmission magnitude (lines 6-9). For instance, by tuning the bandpass filter’s bandwidth (lines 1-5), the heat transfer coefficient can be varied between 47-105 W7(m^A2K) while the heat-electricity efficiency only changes between 42-45%. Furthermore, the bandpass assembly’s transmission magnitude (lines 6-9) may also be varied to tune the heat transfer coefficient nearly independently of the heatelectricity efficiency. The effective heat transfer coefficient or thermal resistance of the TPV system 100 may also be controlled almost independently from the system efficiency.

[0054] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

[0055] Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” may be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

[0056] The many features and advantages of the disclosure are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the disclosure which fall within the true spirit and scope of the disclosure. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the disclosure to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the disclosure.

[0057] In the descriptions above and in the claims, phrases such as “at least one of’ or “one or more of’ may occur followed by a conjunctive list of elements or features. The term “and/or” may also occur in a list of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which it is used, such a phrase is intended to mean any of the listed elements or features individually or any of the recited elements or features in combination with any of the other recited elements or features. For example, the phrases “at least one of A and B;” “one or more of A and B;” and “A and/or B” are each intended to mean “A alone, B alone, or A and B together.” A similar interpretation is also intended for lists including three or more items. For example, the phrases “at least one of A, B, and C;” “one or more of A, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together.” Use of the term “based on,” above and in the claims is intended to mean, “based at least in part on,” such that an unrecited feature or element is also permissible.

[0058] The implementations set forth in the foregoing description do not represent all implementations consistent with the subject matter described herein. Instead, they are merely some examples consistent with aspects related to the described subject matter. Although a few variations have been described in detail herein, other modifications or additions are possible. In particular, further features and/or variations can be provided in addition to those set forth herein. For example, the implementations described above can be directed to various combinations and sub-combinations of the disclosed features and/or combinations and subcombinations of one or more features further to those disclosed herein. In addition, the logic flows depicted in the accompanying figures and/or described herein do not necessarily require the particular order shown, or sequential order, to achieve desirable results. The scope of the following claims may include other implementations or embodiments.

[0059] The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. [0060] While the foregoing is directed to implementations of the present disclosure, other and further implementations of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for filtering light in a thermo-photovoltaic system, the apparatus comprising: a substrate configured to pass light from a first side to a second side, the second side approximately parallel to the first side; a first multilayered structure coupled to the first side of the substrate, the first multilayered structure having at least two layers, the at least two layers comprising at least one of a dielectric multilayer, a semiconductor multilayer, a metallic-dielectric multilayer, a semiconductor-dielectric multilayer, a metallic-semiconductor multilayer, a metallic- semiconductor-dielectric multilayer; and a second multilayered structure coupled to the second side of the substrate, the second multilayered structure having at least two layers, the at least two layers comprising at least one of a dielectric multilayer, a semiconductor multilayer, a metallic-dielectric multilayer, a semiconductor-dielectric multilayer, a metallic-semiconductor multilayer, a metallic- semiconductor-dielectric multilayer, wherein at least a portion of the light is configured to pass through the substrate from the first multilayered structure to the second multilayered structure, and wherein the apparatus is configured to pass light having a wavelength above a first wavelength cutoff, and the apparatus is configured to pass light having a wavelength below a second wavelength cutoff.

2. The apparatus of claim 1, wherein the second side of the substrate has a small angular offset up to 5 degrees relative to the first side of the substrate and wherein the substrate further comprises at least one of silicon, glass, ZnSe, Sapphire, and GaAs.

3. The apparatus of claim 2, wherein the substrate includes a plurality of substrates with each substrate of the plurality of substrates having a different structure, and wherein the glass may include at least one of silicon dioxide, borofloat, UV grade glass, and IR grade glass.

4. The apparatus of claim 1, wherein the at least two layers of the first multilayered structure includes at least one of a highly-doped semiconductor layer and a transparent conducting oxide layer.

5. The apparatus of claim 1, wherein the at least two layers of the second multilayered structure includes at least one of a highly-doped semiconductor layer and a transparent conducting oxide layer.

6. The apparatus of claim 1, wherein the first multilayered structure is a shortpass filter and wherein the second multilayered structure is at least one of a bandpass filter and a longpass filter.

7. The apparatus of claim 1, wherein the first multilayered structure is a bandpass filter and wherein the second multilayered structure is at least one of a shortpass filter, a bandpass filter, a longpass filter, and an antireflection coating.

8. The apparatus of claim 1, wherein the first multilayered structure is a longpass filter and wherein the second multilayered structure is at least one of a shortpass filter and a bandpass filter.

9. The apparatus of claim 1, wherein the first multilayered structure is an antireflection coating and wherein the second multilayered structure is a bandpass filter.

10. The apparatus of claim 1, wherein the apparatus is configured to be interposed between a light emitter and a photovoltaic cell.

11. The apparatus of claim 1, wherein the first wavelength cutoff is greater than or equal to 0.7 pm and the second wavelength cutoff is less than or equal to 10 pm and the difference between the second wavelength cutoff and the first wavelength cutoff is less than or equal to 1.5 pm.

12. A system for filtering light in a thermo-photovoltaic system, the system comprising: a substrate configured to pass light from a first side to a second side, the second side approximately parallel to the first side; a first multilayered structure coupled to the first side of the substrate, the first multilayered structure facing a source of light and having at least two layers, the at least two layers comprising at least one of a dielectric multilayer, a semiconductor multilayer, a metallic-dielectric multilayer, a semiconductor-dielectric multilayer, a metallic- semiconductor multilayer, a metallic-semiconductor-dielectric multilayer; and a second multilayered structure coupled to the second side of the substrate, the second multilayered structure facing a photovoltaic cell and having at least two layers, the at least two layers comprising at least one of a dielectric multilayer, a semiconductor multilayer, a metallic-dielectric multilayer, a semiconductor-dielectric multilayer, a metallic- semiconductor multilayer, a metallic-semiconductor-dielectric multilayer, wherein at least a portion of the light from the source of light is configured to pass through the substrate from the first multilayered structure to the second multilayered structure, and wherein the system is configured to pass light having a wavelength above a first wavelength cutoff and light having a wavelength below a second wavelength cutoff to the photovoltaic cell.

13. The system of claim 12, wherein the second side of the substrate has a small angular offset up to 5 degrees relative to the first side of the substrate, wherein the substrate includes a plurality of substrates with each substrate of the plurality of substrates having a different structure, and wherein the substrate further comprises at least one of silicon, glass, ZnSe, Sapphire, and GaAs.

14. The system of claim 12, wherein the first wavelength cutoff is greater than or equal to 0.7 pm and the second wavelength cutoff is less than or equal to 10 pm and the difference between the second wavelength cutoff and the first wavelength cutoff is less than or equal to 1.5 pm.

15. The system of claim 12, wherein the at least two layers of the first multilayered structure includes at least one of a highly-doped semiconductor layer and a transparent conducting oxide layer.

16. The system of claim 12, wherein the at least two layers of the second multilayered structure includes at least one of a highly-doped semiconductor layer and a transparent conducting oxide layer.

17. The system of claim 12, wherein the first multilayered structure is a shortpass filter and wherein the second multilayered structure is at least one of a bandpass filter and a longpass filter.

18. The system of claim 12, wherein the first multilayered structure is a bandpass filter and wherein the second multilayered structure is at least one of a shortpass filter, a bandpass filter, a longpass filter, and an antireflection coating.

19. The system of claim 12, wherein the first multilayered structure is a longpass filter and wherein the second multilayered structure is at least one of a shortpass filter and a bandpass filter.

20. The system of claim 12, wherein the first multilayered structure is an antireflection coating and wherein the second multilayered structure is a bandpass filter.

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