Photovoltaic cell with light trapping for enhanced efficiency
The efficiency of a photovoltaic cell is enhanced by light trapping using Mie-scattering nanostructures. In one embodiment, an array of nanocylinders is formed on the front surface of a silicon film to enhance forward scattering into the film, and an array of nanocylinders is formed on the back surface to enhance backscattering so that more light is absorbed within the silicon film. In an alternate embodiment, a mirror layer is formed on the back surface of the silicon film to reflect light within the film back toward the front-surface nanocylinder array.
1. A photovoltaic cell, comprising:
a semiconductor film having front and back surfaces;
a photodiode structure defined within the semiconductor film;
a front array of Mie scatterers disposed in a layer proximal the front surface of the semiconductor film, wherein the Mie scatterers are nanocylinders dimensioned to provide enhanced forward scattering of externally incident light in a range of wavelengths effective for photovoltaically stimulating the photodiode structure; and
a rear confinement layer proximal the back surface of the semiconductor film, wherein the rear confinement layer defines a real or effective back array of Mie scatterers.
2. The photovoltaic cell of claim 1 , wherein the rear confinement layer is a mirror layer of metallic material that defines an effective back array of Mie scatterers as a reflective image of the front array of Mie scatterers.
3. The photovoltaic cell of claim 1 , wherein the rear confinement layer comprises a rear array of Mie scatterers, and the Mie scatterers in said rear array are nanocylinders.
4. The photovoltaic cell of claim 3 , wherein the nanocylinders of the front and rear arrays of Mie scatterers have the same dimensions.
5. The photovoltaic cell of claim 1 , wherein the nanocylinders are composed of silicon, germanium, a III-V semiconductor, or a II-VI semiconductor.
6. The photovoltaic cell of claim 1 , wherein the semiconductor film and the nanocylinders are composed of silicon, and the nanocylinders have diameters and heights that are both in the range 200-280 nm.
7. The photovoltaic cell of claim 6 , wherein the silicon semiconductor film is at least 200 nm but not more than 1 μm thick.