A stacked multi-junction solar cell with a first subcell having a top and a bottom, and with a second subcell. The first subcell is implemented as the topmost subcell so that incident light first strikes the top of the first subcell and after that strikes the second subcell through the bottom. A first tunnel diode is arranged between the bottom of the first subcell and the second subcell. A window layer is arranged on the top of the first subcell, and the band gap of the window layer is larger than the band gap of the first subcell. A cover layer is arranged below metal fingers and above the window layer, and an additional layer is arranged below the cover layer and above the window layer. A thickness of the additional layer is less than the thickness of the window layer.

A method for fabricating an upright photovoltaic cell comprises growing one or more epitaxial layers on a substrate, thereby forming a diffused active junction on the substrate and one more additional active junctions above the diffused active junction. The method further comprises selectively etching an areal region of the one or more epitaxial layers, thereby forming a mesa on the substrate and exposing a substrate-contact region parallel to the areal region at a base of the mesa. The method further comprises depositing contact material onto the substrate-contact region, to form the first contact, and concertedly onto a mesa-contact region of the mesa, to form the second contact.

A method for fabricating an upright photovoltaic cell comprises growing one or more epitaxial layers on a substrate, thereby forming a diffused active junction on the substrate and one more additional active junctions above the diffused active junction. The method further comprises selectively etching an areal region of the one or more epitaxial layers, thereby forming a mesa on the substrate and exposing a substrate-contact region parallel to the areal region at a base of the mesa. The method further comprises depositing contact material onto the substrate-contact region, to form the first contact, and concertedly onto a mesa-contact region of the mesa, to form the second contact.

Disclosed is a method of manufacturing a III-V group nanorod solar cell so that a substrate can be reused. The method may includes a first growth process of forming an etch stop layer on a substrate, a second growth process of growing a sacrificial layer on the etch stop layer, a third growth process of forming, on the sacrificial layer, a pattern layer including an opening at each location at which each nanorod solar cell is able to be grown, a fourth growth process of growing the nanorod solar cells on the sacrificial layer through the openings within the pattern layer, a forming process of forming a solar cell protection layer on outsides of the nanorod solar cells, a first etching process of etching the sacrificial layer and the pattern layer, and a second etching process of etching the etch stop layer.

A stacked multi-junction solar cell with a back-contacted front side, having a germanium substrate that forms a rear side of the multi-junction solar cell, a germanium sub-cell and at least two III-V sub-cells, successively in the named order, and at least one passage contact opening that extends from the front side of the multi-junction solar cell through the sub-cells to the rear side and a metallic connection contact that is guided through the passage contact opening. A diameter of the passage contact opening decreases in steps from the front side to the rear side of the multi-junction solar cell. The front side of the germanium sub-cell forms a first step having a first tread depth that circumferentially projects into the passage contact opening. The second step with a second tread depth circumferentially projects into the passage contact opening.

A stacked multi-junction solar cell with a back-contacted front side, having a germanium substrate that forms a rear side of the multi-junction solar cell, a germanium sub-cell and at least two III-V sub-cells, successively in the named order, and at least one passage contact opening that extends from the front side of the multi-junction solar cell through the sub-cells to the rear side and a metallic connection contact that is guided through the passage contact opening. A diameter of the passage contact opening decreases in steps from the front side to the rear side of the multi-junction solar cell. The front side of the germanium sub-cell forms a first step having a first tread depth that circumferentially projects into the passage contact opening. The second step with a second tread depth circumferentially projects into the passage contact opening.

A metamorphic multijunction solar cell having a growth semiconductor substrate with a top surface having a doping in the range of 1x10.sup.18 to 1x10.sup.20 charge carriers/cm.sup.3; a window layer for a top (light facing) subcell formed directly on the top surface of the growth substrate; a sequence of layers of semiconductor material forming a solar cell directly on the window layer; a surrogate substrate on the top surface of the sequence of layers of semiconductor material, wherein a portion of the semiconductor substrate is removed so that only the high doped surface portion of the substrate, having a thickness in the range of 0.5 μm to 10 μm, remains.

A multijunction solar cell including an upper first solar subcell having a first band gap and positioned for receiving an incoming light beam; a second solar subcell disposed below and adjacent to and lattice matched with said upper first solar subcell, and having a second band gap smaller than said first band gap; wherein at least one of the solar cells has a graded band gap throughout its thickness.

A method of passive cooling for a high concentrating photovoltaic, the high concentrating photovoltaic, includes a photovoltaic receiver, a parabolic dish reflector and a plurality of thermally conductive heat pipes having a direct thermal contact between the receiver and the reflector to transfer excessive heat. The method includes receiving sunlight by the parabolic dish reflector, reflecting the sunlight towards the photovoltaic receiver that converts the sunlight into electricity and heat, transferring the heat through the thermally conductive heat pipes and absorbing the heat by the reflector serving a dual purpose as a heat sink. A reduction in weight and cost is accomplished by incorporating the flat heat pipes.

A method of passive cooling for a high concentrating photovoltaic, the high concentrating photovoltaic, includes a photovoltaic receiver, a parabolic dish reflector and a plurality of thermally conductive heat pipes having a direct thermal contact between the receiver and the reflector to transfer excessive heat. The method includes receiving sunlight by the parabolic dish reflector, reflecting the sunlight towards the photovoltaic receiver that converts the sunlight into electricity and heat, transferring the heat through the thermally conductive heat pipes and absorbing the heat by the reflector serving a dual purpose as a heat sink. A reduction in weight and cost is accomplished by incorporating the flat heat pipes.