# US 5,700,332 A · Segregated tandem filter for enhanced conversion efficiency in a thermophotovoltaic energy conversion system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,700,332 A - Document ID: US5700332A - Status: Granted - Kind: A - Application number: 08/678,741 - Filed: 1996-07-11 - Granted: 1997-12-23 - Earliest claimed: 1996-07-11 - Assignees: The United States of America as represented by the United States Department of Energy - Inventors: Edward J. Brown; Paul F. Baldasaro; Randolph J. Dziendziel - Web page: https://patentgrep.com/patent/US5700332A ## CPC - H10F 77/311: {for photovoltaic cells} - H02S 10/30: Thermophotovoltaic systems (photovoltaic cells specially adapted for conversion or sensing of infrared [IR] radiation H10F10/00; thermoelectric devices H10N10/00) - Y02E 10/50: Photovoltaic [PV] energy - H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION - H02S: GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES (obtaining electrical energy from radioactive sources G21H1/12; light sensitive inorganic semiconductor devices H10F; light sensitive organic semiconductor devices H10K30/00; thermoelectric devices H10N10/00; pyroelectric devices H10N15/00) - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract A filter system to transmit short wavelength radiation and reflect long wavelength radiation for a thermophotovoltaic energy conversion cell comprises an optically transparent substrate segregation layer with at least one coherent wavelength in optical thickness; a dielectric interference filter deposited on one side of the substrate segregation layer, the interference filter being disposed toward the source of radiation, the interference filter including a plurality of alternating layers of high and low optical index materials adapted to change from transmitting to reflecting at a nominal wavelength .lambda..sub.IF approximately equal to the bandgap wavelength .lambda..sub.g of the thermophotovoltaic cell, the interference filter being adapted to transmit incident radiation from about 0.5.lambda..sub.IF to .lambda..sub.IF and reflect from .lambda..sub.IF to about 2.lambda..sub.IF ; and a high mobility plasma filter deposited on the opposite side of the substrate segregation layer, the plasma filter being adapted to start to become reflecting at a wavelength of about 1.5.lambda..sub.IF. ## Claims ### Claim 1 A filter system to transmit short wavelength radiation and reflect long wavelength radiation for use with a predetermined thermophotovoltaic energy conversion cell, comprising: a) an optically transparent substrate segregation layer at least one coherence length in optical thickness; b) a dielectric interference filter deposited on one side of said substrate segregation layer, said interference filter adapted to being disposed toward the source of radiation, said interference filter including a plurality of alternating layers of high and low optical index materials adapted to change from transmitting to reflecting at a nominal wavelength .lambda..sub.IF approximately equal to the bandgap wavelength .lambda..sub.g of the thermophotovoltaic cell, said interference filter being adapted to transmit incident radiation from about 0.5.lambda..sub.IF to .lambda..sub.IF and reflect from .lambda..sub.IF to about 2.lambda..sub.IF ; and c) a high mobility plasma filter deposited on the opposite side of said substrate segregation layer, said plasma filter being adapted to start to become reflecting at a wavelength about 1.5.lambda..sub.IF. ### Claim 2 (depends on 1) A filter system as in claim 1, wherein: said alternating layers of said interference filter are made of silicon and silicon monoxide. ### Claim 3 (depends on 1) A filter system as in claim 1, wherein: said high optical index material is selected from the group consisting of silicon, zinc selenide, zinc sulfide, and niobium oxide. ### Claim 4 A filter system as in claim, 1, wherein: said low optical index material is selected from the group consisting of silicon monoxide, cryolite, silicon dioxide, alumina, and magnesium fluoride. ### Claim 5 (depends on 1) A filter system as n claim 1, and further comprising: an optical coupling layer disposed between said substrate segregation layer and said plasma filter, said optical coupling layer being adapted to minimize reflection from about 2.0.lambda..sub.IF to 4.0.lambda..sub.IF. ### Claim 6 (depends on 1) A filter system as in claim 1, wherein: said plasma filter comprises a layer of transparent conducting oxide. ### Claim 7 (depends on 6) A filter system as in claim 6, wherein: said plasma filter is selected from the group consisting of indium-tin oxide, indium oxide, and cadmium stannate. ### Claim 8 (depends on 6) A filter system as in claim 6, wherein: said plasma filter layer comprises a highly doped semiconducting material. ### Claim 9 (depends on 8) A filter system as in claim 8, wherein: a) said highly doped semiconducting material is selected from the group consisting of doped gallium arsenide, gallium antimonide, and silicon; b) the dopant is selected from the group consisting of boron, arsenic, and phosphorus. ### Claim 10 (depends on 1) A filter system as in claim 1, wherein: said plasma filter is fabricated by creating a highly doped region within the opposite side of said substrate segregation layer. ### Claim 11 (depends on 1) A filter system as in claim 1, wherein: said segregation layer is chosen from the group consisting of silicon, zinc selenide, zinc sulfide, thorium fluoride, lead chloride, cerium oxide, lead fluoride, and cryolite. ### Claim 12 (depends on 1) A filter system as in claim 1, wherein: said substrate segregation layer is greater than a coherence length in optical thickness. ### Claim 13 A thermophotovoltaic system, comprising: a) a thermophotovoltaic cell; b) a high mobility plasma filter bonded onto said thermophotovoltaic cell, said plasma filter being adapted to start to become reflecting at a wavelength of about 1.5.lambda..sub.IF, where .lambda..sub.IF is approximately equal to said thermophotovoltaic cell bandgap wavelength .lambda..sub.g ; c) an optically transparent substrate segregation layer disposed on top of said plasma filter, said segregation layer having at least one coherence length in optical thickness; and d) a dielectric interference filter deposited on top of said substrate segregation layer, said interference filter being disposed toward the source of radiation, said interference filter including a plurality of alternating layers of high and low optical index materials adapted to change from transmitting to reflecting at a nominal wavelength .lambda..sub.IF, said interference filter being adapted to transmit incident radiation from about 0.5.lambda..sub.IF to .lambda..sub.IF and reflect from .lambda..sub.IF to about 2.lambda..sub.IF. ### Claim 14 (depends on 13) A thermophotovoltaic system as in claim 13, wherein: said plasma filter is bonded to said thermophotovoltaic cell by means of an optical adhesive. ### Claim 15 (depends on 13) A thermophotovoltaic system as in claim 13, wherein: said plasma filter is directly deposited onto said thermophotovoltaic cell.