A photodetector includes an insulating layer on a substrate, a first graphene layer on the insulating layer, a 2-dimensional (2D) material layer on the first graphene layer, a second graphene layer on the 2D material layer, a first electrode on the first graphene layer, and a second electrode on the second graphene layer. The 2D material layer includes a barrier layer and a light absorption layer. The barrier layer has a larger bandgap than the light absorption layer.

Thin films comprising crystalline Fe.sub.2XY.sub.4, wherein X is Si or Ge and Y is S or Se, are obtained by coating an ink comprised of nanoparticle precursors of Fe.sub.2XY.sub.4 and/or a non-particulate amorphous substance comprised of Fe, X and Y on a substrate surface and annealing the coating. The coated substrate thereby obtained has utility as a solar absorber material in thin film photovoltaic devices.

The invention relates to a material comprising at least one compound having formula Bi.sub.1xM.sub.xAg.sub.1yM.sub.yOS.sub.1zM.sub.z, the methods for producing said material and the use thereof as a semiconductor, such as for photovoltaic or photochemical use and, in particular, for supplying a photocurrent. The invention further relates to photovoltaic devices using said compounds.

Deposition processes are disclosed herein for depositing thin films comprising a dielectric transition metal compound phase and a conductive or semiconducting transition metal compound phase on a substrate in a reaction space. Deposition processes can include a plurality of super-cycles. Each super-cycle may include a dielectric transition metal compound sub-cycle and a reducing sub-cycle. The dielectric transition metal compound sub-cycle may include contacting the substrate with a dielectric transition metal compound. The reducing sub-cycle may include alternately and sequentially contacting the substrate with a reducing agent and a nitrogen reactant. The thin film may comprise a dielectric transition metal compound phase embedded in a conductive or semiconducting transition metal compound phase.

Techniques for achieving band gap grading in CZTS/Se absorber materials are provided. In one aspect, a method for creating band gap grading in a CZTS/Se absorber layer includes the steps of: providing a reservoir material containing Si or Ge; forming the CZTS/Se absorber layer on the reservoir material; and annealing the reservoir material and the CZTS/Se absorber layer under conditions sufficient to diffuse Si or Ge atoms from the reservoir material into the CZTS/Se absorber layer with a concentration gradient to create band gap grading in the CZTS/Se absorber layer. A photovoltaic device and method of forming the photovoltaic device are also provided.

Light-receiving elements and the like that can more simply absorb and transmit light are provided.

A Light-receiving element includes a lens unit condensing incident light to emit the light from an emission surface, an absorption layer arranged on the emission surface of the lens unit to absorb part of the condensed light and transmit the remaining condensed light, and a detection layer placed on the absorption layer to detect intensity of light emitted from the lens unit, on the basis of intensity of light absorbed by the absorption layer.

Provided are a water decomposition apparatus and a water decomposition method that can maintain high gas generation efficiency even in an early stage of light irradiation and even in a case where time has elapsed and that can recover the gas generation amount of hydrogen gas or the like, can generate hydrogen gas or the like stably for a long time on an average, and can increase the integrated amount of generation of hydrogen for a long time, even in a case where time has elapsed and the gas generation amount of hydrogen gas or the like has decreased.

A method for forming a back contact on an absorber layer in a photovoltaic device includes forming a two dimensional material on a first substrate. An absorber layer including CuZnSnS(Se) (CZTSSe) is grown over the first substrate on the two dimensional material. A buffer layer is grown on the absorber layer on a side opposite the two dimensional material. The absorber layer is exfoliated from the two dimensional material to remove the first substrate from a backside of the absorber layer opposite the buffer layer. A back contact is deposited on the absorber layer.

Compound semiconductors, expressed by the following formula: Bi.sub.1-xM.sub.xCu.sub.wO.sub.a-yQ1.sub.yTe.sub.b-zQ2.sub.z. Here, M is at least one element selected from the group consisting of Ba, Sr, Ca, Mg, Cs, K, Na, Cd, Hg, Sn, Pb, Eu, Sm, Mn, Ga, In, Tl, As and Sb; Q1 and Q2 are at least one element selected from the group consisting of S, Se, As and Sb; x, y, z, w, a, and b are 0x<1, 0<w1, 0.2<a<4, 0y<4, 0.2<b<4 and 0z<4. These compound semiconductors may be used for various applications such as solar cells or thermoelectric conversion elements, where they may replace compound semiconductors in common use, or be used along with compound semiconductors in common use.

An electronic device includes a trigonal crystal substrate defining a (0001) C-plane. The substrate may comprise Sapphire or other suitable material. A plurality of rhombohedrally aligned SiGe (111)-oriented crystals are disposed on the (0001) C-plane of the crystal substrate. A first region of material is disposed on the rhombohedrally aligned SiGe layer. The first region comprises an intrinsic or doped Si, Ge, or SiGe layer. The first region can be layered between two secondary regions comprising n+doped SiGe or n+doped Ge, whereby the first region collects electrons from the two secondary regions.