Photovoltaic device with an anti-reflective coating and anti-reflective coating for photovoltaic devices

1 . A photovoltaic device comprising an anti-reflective coating on a light incident side of a transparent cover layer, the anti-reflective coating comprising a layer of diatom frustules, each of the frustules comprising two adjacent and connected porous silica layers,

the first porous silica layer having a pore diameter and pore pitch defining a first layer porosity, the second porous silicon layer having a pore diameter and pore pitch defining a second layer porosity, the second layer porosity being less than the first layer porosity, wherein the pore pitch and pore diameter of the first porous silica layer are each less than the pore pitch and pore diameter of the second porous silica layer,

the layer of diatom frustules being arranged such that the first porous silica layer is light incident with respect to the second porous silica layer.

2 . The photovoltaic device according to claim 1 , wherein the diatoms are pennate diatoms.

3 . The photovoltaic device according to claim 1 , wherein the pore pitch and pore diameter of the first porous silica layer are each substantially less than the wavelength range of visible light, such that the first porous silica layer may be represented by an effective index layer.

4 . The photovoltaic device according to claim 1 , wherein the pore pitch and pore diameter of the second porous silica layer are such that the second porous silica layer it cannot be represented as an effective index layer.

5 . The photovoltaic device according to claim 1 , wherein the frustules consist of the two adjacent and connected porous layers.

6 . The photovoltaic device according to claim 1 , wherein the second porous silica layer has a thickness of from about 50 nm to about 500 nm.

7 . The photovoltaic device according to claim 1 , wherein the porosity of the first porous silica layer is greater than about 20%.

8 . The photovoltaic device according to claim 1 , wherein the pitch of pores in the first porous silica layer is less than about 200 nm.

9 . The photovoltaic device according to claim 1 , wherein the diameter of pores in the first porous silica layer is less than about 200 nm.

10 . An anti-reflective coating for a photovoltaic device, the anti-reflective coating comprising a layer of diatom frustules, each of the frustules comprising two adjacent and connected porous silica layers,

the first porous silica layer having a pore diameter and pore pitch defining a first porosity,

the second porous silicon layer having a pore diameter and pore pitch defining a second porosity, the second porosity being less than the first porosity, wherein the pore pitch and pore diameter of the first porous silica layer are each less than the pore pitch and pore diameter of the second porous silica layer,

the layer of diatom frustules being arranged such that the first porous silica layer is the light incident layer of the anti-reflective coating.

11 . The anti-reflective coating according to claim 10 , wherein the pore pitch and pore diameter of the first porous silica layer are each substantially less than the wavelength of visible light such that the first porous silica layer may be represented as a light effective index layer.

12 . The anti-reflective coating according to claim 10 , wherein the diatoms are pennate diatoms.

13 . The anti-reflective coating according to claim 10 , wherein the frustules consist of the two adjacent and connected porous layers.

14 . The anti-reflective coating according to claim 10 , wherein the second porous silica layer has a thickness of from about 50 nm to about 500 nm.

15 . A method for producing a photovoltaic device comprising a transparent cover layer comprising:

providing the anti-reflective coating according to claim 10 to the light incident side of the transparent cover layer.