VERTICAL PILLAR STRUCTURED PHOTOVOLTAIC DEVICES WITH WAVELENGTH-SELECTIVE MIRRORS

1 . A photovoltaic device operable to convert light to electricity, comprising a substrate, one or more structures essentially perpendicular to the substrate, and a wavelength-selective layer disposed on the substrate, wherein the structures comprise a crystalline semiconductor material.

2 . The photovoltaic device of claim 1 , wherein the structures comprise a doped semiconductor material.

3 . The photovoltaic device of claim 1 , wherein the single crystalline semiconductor material is selected from a group consisting of silicon, germanium, group III-V compound materials, group II-VI compound materials, and quaternary materials.

4 . The photovoltaic device of claim 1 , wherein the structures are cylinders or prisms with a cross-section selected from a group consisting of elliptical, circular, rectangular, and polygonal cross-sections, strips, or a mesh.

5 . The photovoltaic device of claim 1 , wherein the structures are pillars with diameters from 50 nm to 20 μm, heights from 1 μm to 100 μm, a center-to-center distance between two closest pillars of 300 nm to 15 μm.

6 . The photovoltaic device of claim 1 , wherein at least one region the one or more structures has a sidewall, a bottom wall, and a rounded, tapered or beveled inner edge between the sidewall and the bottom wall.

7 . The photovoltaic device of claim 1 , wherein the wavelength-selective layer is electrically conductive.

8 . The photovoltaic device of claim 1 , wherein the wavelength-selective layers are connected.

9 . The photovoltaic device of claim 1 , wherein the wavelength-selective layer is configured as an electrode of the photovoltaic device.

10 . The photovoltaic device of claim 1 , wherein wavelength-selective layer is operable to substantially transmit light of wavelengths above a threshold wavelength and substantially reflect light of wavelengths below the threshold wavelength.

11 . The photovoltaic device of claim 9 , wherein the threshold wavelength is a wavelength between 300 nm and 1100 nm.

12 . The photovoltaic device of claim 1 , wherein the wavelength-selective layer comprises a material selected from a group consisting of ZnO, Al, Au, Ag, Pd, Cr, Cu, Ti, and a combination thereof.

13 . The photovoltaic device of claim 1 , wherein the wavelength-selective layer has a thickness of 15 nm to 30 nm.

14 . The photovoltaic device of claim 1 , wherein the wavelength-selective layer comprises a dichroic mirror and an electrically conductive layer.

15 . The photovoltaic device of claim 1 , wherein the wavelength-selective layer comprises an alternating stack dielectric and electrically conducting layers.

16 . The photovoltaic device of claim 9 , wherein the wavelength-selective layer is configured to substantially reflect light of wavelengths below the threshold wavelength incident on the wavelength-selective layer to the structures so that the light is absorbed by the structures.

17 . The photovoltaic device of claim 1 , further comprising a junction layer, wherein:

the junction layer is a doped semiconductor; and

the junction layer is disposed on the sidewall, on the bottom wall under the wavelength-selective layer, and on a top surface of the structures.

18 . The photovoltaic device of claim 17 , wherein

the structures comprise a doped semiconductor and the structures and the junction layer have opposite conduction types.

19 . The photovoltaic device of claim 17 , wherein the junction layer has a thickness from 5 nm to 200 nm.

20 . The photovoltaic device of claim 17 , wherein the junction layer has a bandgap higher than a bandgap of the structures.

21 . The photovoltaic device of claim 17 , wherein the junction layer is amorphous silicon.

22 . The photovoltaic device of claim 17 , wherein the junction layer is effective to passivate surfaces of the structures.

23 . The photovoltaic device of claim 17 , wherein the junction layer and the structures form a p-n junction.

24 . The photovoltaic device of claim 17 , further comprising an intrinsic layer deposited between the junction layer and the structures, wherein the intrinsic layer is an intrinsic semiconductor.

25 . The photovoltaic device of claim 24 , wherein the intrinsic semiconductor is intrinsic amorphous silicon.

26 . The photovoltaic device of claim 24 , wherein the junction layer, intrinsic layer and the structures form a p-i-n junction.

27 . The photovoltaic device of claim 17 , further comprising, a cladding layer disposed over an entire exposed portion of the junction layer and the wavelength-selective layer.

28 . The photovoltaic device of claim 27 , wherein the cladding layer is substantially transparent to visible light with a transmittance of at least 50%; the cladding layer is made of an electrically conductive material; the cladding layer is a transparent conductive oxide; the cladding layer is a material selected from a group consisting of indium tin oxide, aluminum doped zinc oxide, zinc indium oxide, and zinc tin oxide; the cladding layer has a thickness from 10 nm to 500 nm; the cladding layer forms an Ohmic contact with the wavelength-selective layer; the cladding layer forms an Ohmic contact with the junction layer; and/or the cladding layer is configured as an electrode of the photovoltaic device.

29 . The photovoltaic device of claim 27 , further comprising a coupling layer disposed on the cladding layer.

30 . The photovoltaic device of claim 29 , wherein a refractive index of the structures is greater than a refractive index of the cladding layer; and the refractive index of the cladding layer is greater than refractive index of the coupling layer.

31 . The photovoltaic device of claim 1 , wherein the substrate has a surface opposite the structures, the surface having recesses.

32 . The photovoltaic device of claim 31 , further comprising a doped layer conformally coated on the surface, a passivation layer disposed conformally on some but not all areas of the doped layer, and a metal layer disposed conformally on the doped layer and the passivation layer and forming an Ohmic contact with the doped layer.

33 . The photovoltaic device of claim 32 , wherein the doped layer has the same conduction type from the structures;

the doped layer is electrically connected to at least some of the structures.

34 . The photovoltaic device of claim 32 , wherein the metal layer is configured to reflect essentially all light passing through the substrate back towards the structures.

35 . The photovoltaic device of claim 1 , wherein the substrate has a flat surface opposite the structures.

36 . The photovoltaic device of claim 35 , wherein the flat surface has a doped layer, a passivation layer deposited on the doped layer and a metal layer disposed on and forming an Ohmic contact with the doped layer.

37 . The photovoltaic device of claim 35 , wherein the passivation layer has a plurality of openings.

38 . The photovoltaic device of claim 35 , wherein the metal layer is configured to reflect essentially all light passing through the substrate back towards the structures.

39 . A method of making the photovoltaic device of claim 1 , comprising:

generating a pattern of openings in a resist layer using a lithography technique, wherein locations and shapes of the openings correspond to location and shapes of the structures;

forming the structures by etching the substrate;

depositing the wavelength-selective layer to the bottom wall.

40 . The method of claim 39 , further comprising ion implantation.

41 . The method of claim 39 , wherein the structures are formed by deep etch.

42 . A method of making the photovoltaic device of claim 31 , comprising: anisotropical wet etching.

43 . A method of converting light to electricity comprising:

exposing a photovoltaic device to light, wherein the photovoltaic device comprises a substrate, one or more structures essentially perpendicular to the substrate, and a wavelength-selective layer disposed on the substrate, wherein the structures comprise a single crystalline semiconductor material;

selectively reflecting light to the structures and selectively transmitting light into the substrate, using the wavelength-selective layer;

absorbing the light and converting the light to electricity using the structures and the substrate;

drawing an electrical current from the photovoltaic device.

44 . The method of claim 43 , wherein the electrical current is drawn from the wavelength-selective layer.

45 . A photo detector comprising the photovoltaic device of claim 1 , wherein the photo detector is configured to output an electrical signal when exposed to light.

46 . A method of detecting light comprises:

exposing the photovoltaic device of claim 1 to light;

measuring an electrical signal from the photovoltaic device.

47 . The method of claim 46 , wherein the electrical signal is an electrical current, an electrical voltage, an electrical conductance and/or an electrical resistance.

48 . The method of claim 46 , wherein a bias voltage is applied to the structures in the photovoltaic device.

49 . The photovoltaic device of claim 1 , wherein the crystalline semiconductor material is a single-crystal.