Distributed bragg reflector structures in multijunction solar cells

A method of forming a multijunction solar cell comprising:

• forming an upper and a lower solar subcell each having an emitter and a base layer forming a photoelectric junction;
• and
• forming a near infrared (NIR) wideband reflector layer disposed below the upper subcell and above the lower subcell for reflecting light in the spectral range of 900 to 1050 nm which represents unused and undesired solar energy and thereby reducing the overall solar energy absorptance in the solar cell and providing thermodynamic radiative cooling of the solar cell when deployed in space outside the atmosphere;
• wherein the wideband reflector layers includes a first distributed Bragg reflector (DBR) structure disposed above a tunnel diode layer, wherein the DBR structure and the tunnel diode layer are disposed between the same pair of solar subcells of the multijunction solar cell, the pair of solar subcells having no other solar subcell disposed between them, wherein the DBR structure is composed of a plurality of alternating layers of different semiconductor materials with discontinuities in their respective indices of refraction and arranged so that light can enter and pass through the upper solar subcell and at least a first portion of said light a first spectral wavelength range can be reflected back into the upper solar subcell and out of the solar cell by the first DBR structure, and a second portion of said light in a second spectral wavelength can be transmitted through the first DBR structure to the layers disposed beneath the first DBR structure, wherein the second spectral wavelength range is greater than 1050 nm.

A method of forming a multijunction solar cell comprising:

• forming an upper and a lower solar subcell each having an emitter and a base layer forming a photoelectric junction;
• and
• forming a near infrared (NIR) wideband reflector layer disposed below the upper subcell and directly above the lower subcell for reflecting light in the spectral range of 900 to 1050 nm which represents unused and undesired solar energy and thereby reducing the overall solar energy absorptance in the solar cell and providing thermodynamic radiative cooling of the solar cell when deployed in space outside the atmosphere;
• wherein the wideband reflector layers includes a first distributed Bragg reflector (DBR) structure disposed between a buffer layer and a tunnel diode layer, wherein the buffer layer is a nucleation layer disposed directly above the lower solar subcell, and wherein the DBR structure, the tunnel diode layer, and the buffer layer are disposed between the upper and lower solar subcells of the multijunction solar cell, the upper and lower pair of solar subcells having no other solar subcell disposed between them, wherein the DBR structure is composed of a plurality of alternating layers of different semiconductor materials with discontinuities in their respective indices of refraction and arranged so that light can enter and pass through the upper solar subcell and at least a first portion of said light a first spectral wavelength range can be reflected back into the upper solar subcell and out of the solar cell by the first DBR structure, and a second portion of said light in a second spectral wavelength can be transmitted through the first DBR structure to the layers disposed beneath the first DBR structure, wherein the second spectral wavelength range is greater than 1050 nm.