MULTI-JUNCTION POWER CONVERTER WITH PHOTON RECYCLING
A multi-junction power converter system illuminated by an incident light source includes a multi-layer stack having a plurality of junctions defined by materials having different bandgaps, with an upper junction having a higher bandgap, and junctions therebelow having smaller bandgaps. The upper junction absorbs more of the incident light, whereas lower junctions successively absorb less of the remaining incident light. The junctions below the upper junction are supplied with additional illumination that has been reemitted from previous cells due to photon recycling. Related devices and methods of operation are also discussed.
1 . A multi-junction power converter, said multi-junction power converter comprising:
a multi-junction photovoltaic cell including n junctions defining a stack of n cells, wherein n is an integer greater than 1,
wherein the n junctions have different bandgaps from one another;
wherein one of the n junctions that is positioned in the stack to be closer to an incident light source has a higher bandgap than ones of the n junctions positioned therebelow, which have progressively smaller bandgaps with distance from the incident light source;
wherein the one of the n junctions that is positioned to be closer to the incident light source is configured to absorb more than 1/n of incident light, and wherein a next one of the n junctions positioned therebelow in the stack is configured to absorb more than 1/(n−1) of remaining incident light, such that the ones of the n junctions are configured to progressively absorb reduced incident light with distance from the incident light source; and
wherein the ones of the n junctions are configured to be supplied with additional illumination that has been reemitted from one of the n junctions thereabove to produce photon recycling.
2 . The multi-junction power converter of claim 1 , wherein said photon recycling in said multi-junction power converter is configured to distribute current generation substantially equally among the n cells.
3 . The multi-junction power converter of claim 1 , wherein said incident light source is a laser.
4 . The multi-junction power converter of claim 1 , wherein the incident light source is a broad band light source comprising an LED or an LED in combination with a phosphor.
5 . The multi-junction power converter of claim 1 , wherein the n junctions comprise InGaP, GaAs, and InGaAsN, respectively.
6 . The multi-junction power converter of claim 1 , wherein the n junctions comprise InGaP, GaAs, and Ge, respectively.
7 . A multi-junction power converter, comprising:
a multi-junction photovoltaic cell that includes n junctions that define a stack of cells,
wherein the n junctions have similar bandgaps;
wherein outer ones of the n junctions in the stack are configured to absorb less than 1/n of incident light;
wherein inner ones of the n junctions in the stack are configured to absorb more than 1/n of the incident light;
wherein the outer ones of the n junctions are configured to be supplied with additional illumination that has been reemitted from the inner ones of the n junctions to produce photon recycling; and
wherein current generation responsive to said incident light and said photon recycling is substantially equal among the cells of the stack.
8 . The multi-junction power converter of claim 7 , wherein said incident light is provided by a laser light source.
9 . The multi-junction power converter of claim 7 , wherein said incident light is provided by an LED light source or an LED plus phosphor light source.
10 . The multi-junction power converter of claim 7 , wherein said photon recycling is configured to provide a higher efficiency than that provided by cells having respective thicknesses optimized for a single illumination wavelength.
11 . A multi-junction photovoltaic cell, comprising:
a multi-layer stack comprising a plurality of photovoltaic cells that are electrically connected, wherein the photovoltaic cells respectively comprise materials having different bandgaps and are vertically stacked in order of decreasing bandgap relative to a surface of the multi-layer stack that is configured to receive incident illumination,
wherein one of the photovoltaic cells closer to the incident illumination is configured to emit photons responsive to the incident light, and wherein one of the photovoltaic cells further from the incident illumination is configured to absorb the photons emitted from the one of the photovoltaic cells closer to the incident illumination,
and wherein the photovoltaic cells are configured to generate respective output currents that are substantially equal.
12 . The multi-junction photovoltaic cell of claim 11 , wherein the photovoltaic cells are configured to generate respective currents that are unequal in response to the incident illumination, and wherein the respective currents comprise portions of the respective output currents.
13 . The multi-junction photovoltaic cell of claim 12 , wherein at least one of the photovoltaic cells comprises a bandgap that is substantially mismatched with respect to a wavelength of the incident illumination such that absorption of the incident illumination is unequal among the photovoltaic cells.
14 . The multi-junction photovoltaic cell of claim 13 , wherein the incident illumination comprises narrowband or single-wavelength light.
15 . The multi-junction photovoltaic cell of claim 13 , wherein the incident illumination comprises broadband light.
16 . The multi-junction photovoltaic cell of claim 12 , wherein at least one of the photovoltaic cells comprises a thickness such that absorption of the incident illumination is unequal among the photovoltaic cells.
17 . The multi-junction photovoltaic cell of claim 12 , wherein the photovoltaic cells are lattice-matched with ones of the photovoltaic cells thereabove and therebelow in the multi-layer stack.
18 . The multi-junction photovoltaic cell of claim 11 , wherein the photovoltaic cells comprise InGaP, GaAs, and GaInNAsSb, respectively.
19 . The multi-junction photovoltaic cell of claim 11 , wherein the photovoltaic cells comprise AlGaAs, InGaAlP, and Ge, respectively.