Submicron gap thermophotovoltaic structure and fabrication method
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 an evacuated 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 adjoined to a first surface of one or more photovoltaic cell substrates by an adhesion layer having a refractive index greater than 1.4 and high transmissivity for infrared radiation; and
the radiation-transparent window substrate having a high refractive index that is equal to or greater than the refractive index of the infrared radiation-emitting substrate and the one or more photovoltaic cell substrates for improved collection and transmission of infrared energy from the infrared radiation-emitting internal surface of the infrared radiation-emitting substrate to the one or more photovoltaic cell substrates.
2. The structure of claim 1 wherein said structure is enclosed in an evacuated housing.
3. The structure of claim 1 wherein the adhesion layer adjoins the radiation-transparent window substrate second surface outside the gap space to the photovoltaic cell first surface.
4. The structure of claim 1 wherein the radiation-transparent window substrate is transparent to radiation emitted by the infrared radiation-emitting substrate, having 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 adhesion layer is free of voids, cracks or delamination.
6. 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.
7. The structure of claim 3 wherein a material of the adhesion layer is selected from the group consisting of epoxies, filled elastomers, and solder glasses including those containing lead oxide, and chalcogenide glasses.
8. The structure of claim 3 wherein a plurality of photovoltaic cells are adjoined to a common radiation-transparent window substrate.
9. The structure of claim 1 wherein the adjoined to a surface of a photovoltaic cell substrate is effected with an adhesion 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 adjoining a common radiation-transparent window substrate to a plurality of photovoltaic cell substrates by an interposed compliant adhesion layer.
10. The structure of claim 9 wherein the adhesion layer is made free of voids, cracks and delaminations.
11. The structure of claim 9 wherein a refractive index of the adhesion layer is greater than 1.4 and is highly transmitting at infrared frequencies.
12. The structure of claim 9 wherein a material of the adhesion layer is selected from the group consisting of epoxies, filled elastomers, and solder glasses including those containing lead oxide, and chalcogenide glasses.
13. The structure of claim 1 wherein the radiation-transparent window substrate is 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.
14. The structure of claim 1 wherein the adhesion layer is a direct bond selected from the group consisting of low temperature bonding, anodic bonding, vacuum bonding and intermolecular bonding.
15. The structure of claim 1 further comprising an array of spacers located between a hot side surface and a cold side surface for maintaining the sub-micron gap, the location of the array of spacers array selected from the group consisting of the cold side surface and the hot side surface.
16. The structure of claim 1 further comprising an array of spacers located between the infrared radiation-emitting 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 infrared radiation-emitting internal surface.
17. The structure of claim 1 further comprising an array of spacers located between the infrared radiation-emitting 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.
18. The structure of claim 1 wherein the infrared radiation-emitting substrate is a refractory material substrate.
19. The structure of claim 1 wherein the infrared radiation-emitting substrate is a zirconia material substrate.
20. The structure of claim 1 wherein the infrared radiation-emitting internal surface is a deposited selective emitting material.
21. The structure of claim 1 wherein the infrared radiation-emitting internal surface is a deposited tungsten silicide material.
22. The structure of claim 1 wherein the radiation-transparent window substrate is transparent to the radiation emitted by the infrared radiation-emitting substrate.
23. The structure of claim 1 wherein a means for adjusting uniformity of the gap comprises the radiation-transparent window substrate second surface affixed to surfaces of a plurality of photovoltaic cells by an adhesive layer, a thickness of the adhesive layer being uniform over the radiation-transparent window substrate second surface.
24. An MTPV thermophotovoltaic chip for generating electrical power, comprising:
a radiation-transparent window substrate having a second surface adjoined to a first surface of one or more photovoltaic cell substrates by an adhesion layer having a refractive index greater than 1.4 and high transmissivity for infrared radiation;
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 an evacuated sub-micron gap; and
the radiation-transparent window substrate having a high index of refraction that is equal to or greater than the refractive index of the infrared radiation-emitting substrate and the one or more photovoltaic cell substrates for improved collection and transmission of infrared energy from the infrared radiation-emitting internal surface of the infrared radiation-emitting substrate to the one or more photovoltaic cell substrates.
25. The MTPV thermophotovoltaic chip of claim 24 , wherein the radiation-transparent window substrate is a single-crystal wafer with overall flatness for maintaining a uniform gap over a large area.
26. The MTPV thermophotovoltaic chip of claim 25 wherein a single radiation-transparent window substrate provides a uniform gap for a plurality of photovoltaic cells.
27. The MTPV thermophotovoltaic chip of claim 24 wherein the adhesion layer provides an insulating base for integrating wires and bypass diodes into the MTPV thermophotovoltaic chip.
28. The MTPV thermophotovoltaic chip of claim 24 wherein the adhesion layer is a direct bond selected from the group consisting of low temperature bonding, anodic bonding and vacuum bonding.
29. The MTPV thermophotovoltaic chip of claim 24 further comprising an array of spacers located between a hot side surface and a cold side surface for maintaining the sub-micron gap, the location of the array of spacers array selected from the group consisting of the cold side surface and the hot side surface.
30. The MTPV thermophotovoltaic chip of claim 24 further comprising an array of spacers located between the infrared radiation-emitting 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 infrared radiation-emitting internal surface.
31. The MTPV thermophotovoltaic chip of claim 24 further comprising an array of spacers located between the infrared radiation-emitting 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.
32. The MTPV thermophotovoltaic chip of claim 24 wherein the infrared radiation-emitting substrate is a refractory material substrate.
33. The MTPV thermophotovoltaic chip of claim 24 wherein the infrared radiation-emitting substrate is a zirconia material substrate.
34. The MTPV thermophotovoltaic chip of claim 24 wherein the infrared radiation-emitting internal surface is a deposited selective emitting material.
35. The MTPV thermophotovoltaic chip of claim 24 wherein the infrared radiation-emitting internal surface is a deposited tungsten silicide material.
36. The MTPV thermophotovoltaic chip of claim 24 wherein the material for the radiation-transparent window substrate is transparent to the radiation emitted by the infrared radiation-emitting substrate.