Structures for increased current generation and collection in solar cells with low absorptance and/or low diffusion length

A solar cell device comprising:

• a substrate comprising a front side surface and a backside surface;
• an epitaxial region overlying the substrate, wherein the epitaxial region comprises a first Bragg reflector disposed below a first solar cell and formed directly on the front side surface of the substrate, wherein the first solar cell comprises a dilute nitride composition and has a first bandgap, the first Bragg reflector is operable to reflect a first range of radiation wavelengths back into the first solar cell and to cool the solar cell device by reflecting a second range of radiation wavelengths that are outside a photogeneration wavelength range of the first solar cell or a third range of radiation wavelengths that are less than 50% absorbed by the first solar cell, and the first Bragg reflector comprises a plurality of repeating and alternating layers having different refractive indexes and a tunnel junction formed between a p-type layer and an n-type layer of the first Bragg reflector, wherein the tunnel junction comprises a p-type doped AlGaAs layer and an n-type doped GaAs layer;
• a capping layer disposed above a top surface of the first solar cell;
• a first metal contact disposed below the backside surface;
• and
• a second metal contact disposed above a top surface of the capping layer.