A photonic bandgap structure having multiple stacked layers has a thickness from the top of its top layer to the bottom of its bottom layer of less than one micron. Metal conducting layers having negative real dielectric constants are positioned between semiconductor layers having positive dielectric constants. The layers are arranged and stacked, and the thicknesses and materials for the semiconductor layers and conductive layers are selected to realize desired absorption, transmission, and reflection characteristics.

An optoelectronic semiconductor device is disclosed. The optoelectronic device comprises a plurality of stacked p-n junctions. The optoelectronic semiconductor device includes a n-doped layer disposed below the p-doped layer to form a p-n layer such that electric energy is created when photons are absorbed by the p-n layer. Recesses are formed on top of the p-doped layer at the top of the plurality of stacked p-n junctions. The junctions create an offset and an interface layer is formed on top of the p-doped layer at the top of the plurality stacked p-n junctions. The optoelectronic semiconductor device also includes a window layer disposed below the plurality stacked p-n junctions. In another aspect, one or more optical filters are inserted into a multi-junction photovoltaic device to enhance its efficiency through photon recycling.

A solar cell that capable of improving light utilization efficiency is disclosed. The solar cell comprises I-VII compound photovoltaic layer, silicon photovoltaic layer, first electrode and second electrode. The I-VII compound photovoltaic layer comprises first and second type I-VII compound layers. The first and second type I-VII compound layer have first and second type impurities, respectively. The second type I-VII compound layer is disposed under the first type I-VII compound layer. The silicon photovoltaic layer comprises first and second type silicon layers. The first and second type silicon layers have first and second type dopants, respectively. The first type and second type silicon layers are disposed under the second type I-VII compound layer and the first type silicon layer, respectively. The first and second electrodes are formed under the second type silicon layer and on a portion of the first type I-VII compound layer, respectively.

A solar cell that capable of improving light utilization efficiency is disclosed. The solar cell comprises I-VII compound photovoltaic layer, silicon photovoltaic layer, first electrode and second electrode. The I-VII compound photovoltaic layer comprises first and second type I-VII compound layers. The first and second type I-VII compound layer have first and second type impurities, respectively. The second type I-VII compound layer is disposed under the first type I-VII compound layer. The silicon photovoltaic layer comprises first and second type silicon layers. The first and second type silicon layers have first and second type dopants, respectively. The first type and second type silicon layers are disposed under the second type I-VII compound layer and the first type silicon layer, respectively. The first and second electrodes are formed under the second type silicon layer and on a portion of the first type I-VII compound layer, respectively.

A germanium single-crystal wafer comprises silicon with an atomic concentration of from 3×10.sup.14 atoms/cc to 10×10.sup.13 atoms/cc, boron with an atomic concentration of from 1×10.sup.16 atoms/cc to 10×10.sup.18 atoms/cc, and gallium with an atomic concentration of from 1×10.sup.16 atoms/cc to 10×10.sup.19 atoms/cc. Further provided are a method for preparing the germanium single-crystal wafer, a method for preparing a germanium single-crystal ingot, and the use of the germanium single-crystal wafer for increasing the open-circuit voltage of a solar cell. The germanium single-crystal wafer has an improved electrical property in that it has a smaller difference in resistivity and carrier concentration.

A method of manufacturing a solar cell comprising: providing a growth substrate depositing on the growth substrate an epitaxial sequence of layers of semiconductor material forming at least a first and second solar subcells depositing a semiconductor contact layer on top of the second solar subcell depositing a reflective metal layer over said semiconductor contact layer such that the reflectivity of the reflective metal layer is greater than 80% in the wavelength range 850 to 2000 nm depositing a contact metal layer composed on said reflective metal layer mounting and bonding a supporting substrate on top of the contact metal layer and removing the growth substrate.

A method of manufacturing a solar cell comprising: providing a growth substrate depositing on the growth substrate an epitaxial sequence of layers of semiconductor material forming at least a first and second solar subcells depositing a semiconductor contact layer on top of the second solar subcell depositing a reflective metal layer over said semiconductor contact layer such that the reflectivity of the reflective metal layer is greater than 80% in the wavelength range 850 to 2000 nm depositing a contact metal layer composed on said reflective metal layer mounting and bonding a supporting substrate on top of the contact metal layer and removing the growth substrate.

Methods and apparatuses for creating solar cell assemblies with bonded interlayers are disclosed. In summary, the present invention describes an apparatus and method for making a solar cell assembly with transparent conductive bonding interlayers. An apparatus in accordance with the present invention comprises a substrate, a first solar cell, coupled to a first side of the substrate, wherein the first solar cell comprises a first Transparent Conductive Coating (TCC) layer coupled to a first polarity electrode of the first solar cell, and a second solar cell, the second solar cell being bonded to the first solar cell by bonding the first TCC layer to the second solar cell.

Methods and apparatuses for creating solar cell assemblies with bonded interlayers are disclosed. In summary, the present invention describes an apparatus and method for making a solar cell assembly with transparent conductive bonding interlayers. An apparatus in accordance with the present invention comprises a substrate, a first solar cell, coupled to a first side of the substrate, wherein the first solar cell comprises a first Transparent Conductive Coating (TCC) layer coupled to a first polarity electrode of the first solar cell, and a second solar cell, the second solar cell being bonded to the first solar cell by bonding the first TCC layer to the second solar cell.

A multijunction solar cell includes an InGaAs buffer layer and an InGaAlAs grading interlayer disposed below, and adjacent to, the InGaAs buffer layer. The grading interlayer achieves a transition in lattice constant from one solar subcell to another solar subcell.