There is provided a photovoltaic device that comprises a photoactive region, the photoactive region comprising a perovskite material of general formula A.sub.1-xA′.sub.xBX.sub.3-yX′.sub.y, wherein A is a formamidinium cation (HC(NH).sub.2).sub.2.sup.+), A′ is a caesium cation (Cs.sup.+) B is at least one divalent inorganic cation, X is iodide and X is bromide, and x is greater than 0 and equal to or less than 0.4 and y is greater than 0 and less than or equal to 3. There is also provided a method of producing a photovoltaic device comprising a photoactive region comprising the perovskite material, and formulations for use in the formation of the perovskite material.

There is provided a photovoltaic device that comprises a photoactive region, the photoactive region comprising a perovskite material of general formula A.sub.1-xA′.sub.xBX.sub.3-yX′.sub.y, wherein A is a formamidinium cation (HC(NH).sub.2).sub.2.sup.+), A′ is a caesium cation (Cs.sup.+) B is at least one divalent inorganic cation, X is iodide and X is bromide, and x is greater than 0 and equal to or less than 0.4 and y is greater than 0 and less than or equal to 3. There is also provided a method of producing a photovoltaic device comprising a photoactive region comprising the perovskite material, and formulations for use in the formation of the perovskite material.

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 forming a photovoltaic device that includes ion implanting a first conductivity type dopant into first regions of a semiconductor layer of an SOI substrate, wherein the first regions are separated by a first pitch; and ion implanting a second conductivity type dopant into second regions of the semiconductor layer of the SOI substrate. The second regions are separated by a second pitch. Each second conductivity type implanted region of the second regions is in direct contact with first conductivity type implanted region of the first regions to provide a plurality of p-n junctions, and adjacent p-n junctions are separated by an intrinsic portion of the semiconductor layer to provide P-I-N cells that are horizontally oriented.

A method of forming a photovoltaic device that includes ion implanting a first conductivity type dopant into first regions of a semiconductor layer of an SOI substrate, wherein the first regions are separated by a first pitch; and ion implanting a second conductivity type dopant into second regions of the semiconductor layer of the SOI substrate. The second regions are separated by a second pitch. Each second conductivity type implanted region of the second regions is in direct contact with first conductivity type implanted region of the first regions to provide a plurality of p-n junctions, and adjacent p-n junctions are separated by an intrinsic portion of the semiconductor layer to provide P-I-N cells that are horizontally oriented.

A multijunction solar cell including a substrate and a top (or light-facing) solar subcell having an emitter layer, a base layer, and a window layer adjacent to the emitter layer, the window layer composed of a material that is optically transparent, has a band gap of greater than 2.6 eV, and includes an appropriately arranged multilayer antireflection coating on the top surface thereof.

A multijunction solar cell including a substrate and a top (or light-facing) solar subcell having an emitter layer, a base layer, and a window layer adjacent to the emitter layer, the window layer composed of a material that is optically transparent, has a band gap of greater than 2.6 eV, and includes an appropriately arranged multilayer antireflection coating on the top surface thereof.

A multijunction solar cell comprising a first solar subcell having a first band gap; a second solar subcell disposed adjacent to said first solar subcell and including an emitter layer, and a base layer having a second band gap less than the first band gap, and being lattice mismatched with the upper first solar subcell, and an intermediate layer directly adjacent to and disposed between first and the second solar subcells and compositionally graded to lattice match the first solar subcell on one side and the second solar subcell on the other side, and arranged so that light can enter and pass through the first solar subcell and at least a portion of which can be reflected back into the first solar subcell by the intermediate layer, and is composed of a plurality of layers of materials with discontinuities in their respective indices of refraction.

A multijunction solar cell comprising a first solar subcell having a first band gap; a second solar subcell disposed adjacent to said first solar subcell and including an emitter layer, and a base layer having a second band gap less than the first band gap, and being lattice mismatched with the upper first solar subcell, and an intermediate layer directly adjacent to and disposed between first and the second solar subcells and compositionally graded to lattice match the first solar subcell on one side and the second solar subcell on the other side, and arranged so that light can enter and pass through the first solar subcell and at least a portion of which can be reflected back into the first solar subcell by the intermediate layer, and is composed of a plurality of layers of materials with discontinuities in their respective indices of refraction.

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.