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.

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 transceiver assembly for a wireless power transfer system includes a transceiver system comprising a photodiode assembly, a voltage converter and a light emitting diode and a photodiode. The photodiode assembly may be configured to receive a high-power laser beam from a transmitter and to convert the high-power laser beam to electrical energy. The voltage converter may be configured to adjust an input impedance based on a voltage measure of the photodiode assembly so as to maximize power transfer from the photodiode assembly to an energy storage device electrically coupled to the voltage converter. The light emitting diode and the photodiode may be configured to enable free space optical communication with the transmitter. The light emitting diode may emit signals indicating a presence and a location of the transceiver to the transmitter at least when the energy storage device requires a charge.

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 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 an emitter and base layers forming a photoelectric junction; a second solar subcell disposed under and adjacent to the upper first solar subcell, and having an emitter and base layers forming a photoelectric junction; and a third solar subcell disposed under and adjacent to the second solar subcell and having an emitter and base layers forming a photoelectric junction; wherein at least one of the base and emitter layers of at least a particular solar subcell from among the upper first solar subcell, the second solar subcell, and the third solar subcell has a graded band gap throughout at least a portion of thickness of its active layer adjacent to the photoelectric junction and being in a range of 20 to 300 MeV greater than a band gap in the active layer away from the photoelectric junction.

A multijunction solar cell including an upper first solar subcell having an emitter and base layers forming a photoelectric junction; a second solar subcell disposed under and adjacent to the upper first solar subcell, and having an emitter and base layers forming a photoelectric junction; and a third solar subcell disposed under and adjacent to the second solar subcell and having an emitter and base layers forming a photoelectric junction; wherein at least one of the base and emitter layers of at least a particular solar subcell from among the upper first solar subcell, the second solar subcell, and the third solar subcell has a graded band gap throughout at least a portion of thickness of its active layer adjacent to the photoelectric junction and being in a range of 20 to 300 MeV greater than a band gap in the active layer away from the photoelectric junction.

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 subcells has a graded band gap throughout the thickness of at least a portion of the active layer.

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 subcells has a graded band gap throughout the thickness of at least a portion of the active layer.

Systems and methods of three-terminal tandem solar cells are described. Three-terminal metal electrodes can be formed to contact subcells of the tandem solar cell. The three-terminal tandem cell can improve the device efficiency to at least 30%.