LIGHT HARVESTING SYSTEM EMPLOYING SURFACE FEATURES FOR EFFICIENT LIGHT TRAPPING
A light harvesting system employing a photoresponsive layer having a plurality of light input ports that are formed in a light input surface of the layer. Light received by the light input ports is admitted into the photoresponsive layer an incidence angle that is greater than a predetermined critical angle, such as the angle of the total internal reflection (TIR). The admitted light is retained in the photoresponsive layer and is propagated within the layer until it is substantially absorbed.
1 . A light harvesting system, comprising:
a generally planar layer of photoresponsive material having a generally smooth light input surface; and
a plurality of light input ports distributed over said light input surface,
wherein each of said light input ports is configured to admit light into said layer at an incidence angle that is greater than a predetermined critical angle.
2 . A system as recited in claim 1 , wherein said predetermined critical angle is an angle of the total internal reflection (TIR) characterizing at least one surface of said layer.
3 . A system as recited in claim 1 , wherein each of said plurality of light input ports is formed by a surface feature selected from the group consisting of surface interruptions, recesses, indentations, cavities, through holes, blind holes, grooves, diffraction gratings, holograms, textured areas, and light scattering elements.
4 . A system as recited in claim 1 , wherein each of said plurality of light input ports is configured to trap light within said layer by at least enhancing the propagation path length through said photoresponsive material.
5 . A system as recited in claim 1 , wherein said layer of photoresponsive material is a part of a photovoltaic cell.
6 . A system as recited in claim 5 further comprising at least one electrical contact.
7 . A system as recited in claim 6 , wherein said electrical contact is made from an optically transmissive electroconductive material.
8 . A system as recited in claim 6 , wherein said electrical contact is made from an opaque electroconductive material.
9 . A system as recited in claim 5 , further comprising a plurality of spaced apart electrical contacts, wherein said light input ports are formed in spaces between said electrical contacts.
10 . A system as recited in claim 1 , further comprising a planar array of light focusing elements disposed in energy exchange relationship with said plurality of light input ports.
11 . A system as recited in claim 10 , wherein said planar array of light focusing elements is formed by an array of micro-lenses made from glass or polymeric material.
12 . A system as recited in claim 11 , wherein each of the micro-lenses has a configuration selected from the group consisting of linear, round, rectangular, square, and hexagonal.
13 . A system as recited in claim 11 , wherein each micro-lens has a convex spherical shape and wherein the thickness T of the micro-lens array is defined by the following expression:
T
≈
nR
n
-
1
,
where R is the radius of curvature of the micro-lens and n is the refractive index of the material of said array of microlenses.
14 . A system as recited in claim 10 , wherein each of said plurality of light input ports is disposed in a predetermined alignment with each of said plurality of light focusing elements.
15 . A system as recited in claim 10 , wherein said plurality of light input ports is disposed at a focal distance from said plurality of light focusing elements.
16 . A system as recited in claim 1 , wherein each of said plurality of light input ports comprises one or more refractive face inclined at an angle with respect to the prevailing plane of said photoresponsive layer.
17 . A system as recited in claim 1 , further comprising an optically transmissive buffer layer disposed between said photoresponsive layer and said focusing array.
18 . A system as recited in claim 1 , further comprising means for scattering light propagating in said photoresponsive layer.
19 . A system as recited in claim 1 , further comprising an anti-reflective layer.
20 . A system as recited in claim 1 , further comprising additional means for trapping light within said photoresponsive layer.