Sub-micrometer gap thermophotovoltaic structure (MTPV) and fabrication method therefor
An MTPV thermophotovoltaic chip comprising a photovoltaic cell substrate, micron/sub-micron gap-spaced from a juxtaposed heat or infrared radiation-emitting substrate, with a radiation-transparent intermediate window substrate preferably compliantly adhered to the photovoltaic cell substrate and bounding the gap space therewith.
1. A sub-micron gap thermophotovoltaic structure for generating electrical power, comprising:
an infrared radiation-emitting substrate having an external surface for receiving energy from a heat source and an opposing infrared radiation-emitting internal surface juxtaposed from a first surface of a radiation-transparent window substrate by a sub-micron gap;
a radiation-transparent window substrate second surface opposing the radiation-transparent window substrate first surface, the radiation-transparent window substrate second surface affixed to a surface of a photovoltaic cell substrate by an adhesion layer having a capability of up-conversion of low-energy photons and high transmissivity in at infrared frequencies;
the radiation-transparent window substrate having a refractive index that is equal to or greater than the refractive index of the infrared radiation-emitting substrate and the photovoltaic cell substrate as a means for improved collection and transmission of infrared energy from the infrared radiation-emitting internal surface of the infrared radiation-emitting substrate to the photovoltaic cell substrate; and
the radiation-transparent window substrate being transparent to the radiation emitted by the infrared radiation-emitting substrate and selected from the group of materials consisting of single crystalline semi-insulating GaAs, single crystalline semi-insulating InP, float-zone Si, and lightly doped Si.
2. The structure of claim 1 wherein said structure is enclosed in an evacuated housing.
3. The structure of claim 1 wherein the adhesive layer attaches the radiation-transparent window substrate second surface outside the gap space to the photovoltaic cell.
4. The structure of claim 3 wherein the radiation-transparent window substrate is transparent to radiation emitted by the infrared radiation-emitting substrate, requiring a band gap larger than the infrared, greater than about 1.0 electron-volt and a low density of free carriers or defects.
5. The structure of claim 3 wherein the adhesive layer is free of voids, cracks or delamination.
6. The structure of claim 3 wherein the radiation-transparent window substrate exhibits a refractive index equal to or larger than that of the infrared radiation-emitting and photovoltaic cell substrates.
7. The structure of claim 6 where the refractive index of the adhesive layer is greater than 1.4 and is highly transmitting at infrared frequencies.
8. The structure of claim 3 wherein a material of the radiation-transparent window substrate is selected from the group consisting of single crystalline semi-insulating GaAs, single crystalline semi-insulating InP, float-zone Si, or lightly doped Si.
9. The structure of claim 7 wherein the adhesive layer exhibits compliancy.
10. The structure of claim 7 wherein a material of the adhesive layer is selected from the group consisting of epoxies, filled elastomers, and solder glasses including those containing lead oxide, and chalcogenide glasses.
11. The structure of claim 7 wherein the adhesive layer serves a further function of enabling up-conversion of incoming photons.
12. The structure of claim 11 wherein material introduced into the adhesive layer to enable up-conversion is selected from the group consisting of rare earth ions based on yttrium and erbium elements, compounds based on yttrium and erbium elements and semiconductor quantum dots.
13. The structure of claim 7 wherein a plurality of photovoltaic cells are attached to a common radiation-transparent window substrate.
14. The structure of claim 1 wherein the affixed to a surface of a photovoltaic cell substrate is effected with an adhesive layer attaching the radiation-transparent window substrate second surface outside the gap to the photovoltaic cell substrate, a means of adjusting uniformity of the gap comprising a means for attaching a common radiation-transparent window substrate to a plurality of photovoltaic cell substrates by an interposed compliant adhesive layer, and a means for adjusting the compliant adhesive layer uniformly over the radiation-transparent window substrate second surface.
15. The structure of claim 14 wherein the adhesive layer is made free of voids, cracks and delaminations.
16. The structure of claim 14 wherein a refractive index of the adhesive layer is greater than 1.4 and is highly transmitting at infrared frequencies.
17. The structure of claim 14 wherein a material of the adhesive layer is selected from the group consisting of epoxies, filled elastomers, and solder glasses including those containing lead oxide, and chalcogenide glasses.
18. The structure of claim 1 , further comprising an array of spacers located between the infrared radiation-emitting substrate internal surface and the first surface of the radiation-transparent window substrate for maintaining the sub-micron gap, the array of spacers being formed on the first surface of the radiation-transparent window substrate.
19. An MTPV thermophotovoltaic chip for generating electrical power, comprising:
a radiation-transparent window substrate having a second surface affixed to a surface of a photovoltaic cell substrate by a high-transmissivity adhesive layer with up-conversion capability for low energy photons;
a first surface opposite the second surface of the radiation-transparent window substrate, the first surface of the radiation-transparent window substrate juxtaposed from an infrared radiation-emitting internal surface of an infrared radiation-emitting substrate by a sub-micron gap; and
the radiation-transparent window substrate having a high index of refraction for improved collection and transmission of infrared energy from the infrared radiation-emitting internal surface of the infrared radiation-emitting substrate, wherein material for the radiation-transparent window substrate is transparent to the radiation emitted by the infrared radiation-emitting substrate and is selected from the group consisting of single crystalline semi-insulating GaAs, single crystalline semi-insulating InP, float-zone Si, and lightly doped Si.
20. The MTPV thermophotovoltaic chip of claim 19 , wherein the high-transmissivity adhesive layer provides the up-conversion of incoming photons from the radiation-transparent window substrate to the photovoltaic cell.
21. The MTPV thermophotovoltaic chip of claim 19 , wherein material included in the adhesive layer to enable up-conversion of photons is selected from the group consisting of rare earth ions based on yttrium and erbium elements, rare earth compounds based on yttrium and erbium elements and semiconductor quantum dots.
22. The MTPV thermophotovoltaic chip of claim 19 , wherein the sub-micron gap is evacuated.
23. The MTPV thermophotovoltaic chip of claim 19 , wherein the radiation-transparent window substrate is a single-crystal wafer with overall flatness for maintaining a uniform gap over a large area.
24. The MTPV thermophotovoltaic chip of claim 23 , wherein a single radiation-transparent window substrate provides a uniform gap for a plurality of photovoltaic cells.
25. The MTPV thermophotovoltaic chip of claim 19 , wherein the adhesive layer provides an insulating base for integrating wires and bypass diodes into the MTPV thermophotovoltaic chip.
26. The MTPV thermophotovoltaic chip of claim 19 , wherein the adhesive layer is compliant for maintaining a uniform gap when affixed to one or more photovoltaic cells having irregular surfaces.