BACK SURFACE FIELD FORMATION IN SILICON MICROSPHERES IN A PHOTOVOLTAIC PANEL
A PV panel is manufactured using a monolayer of small silicon sphere diodes (10-300 microns in diameter) connected in parallel. The spheres are embedded in an uncured aluminum-containing layer on an aluminum foil substrate in a roll-to-roll process, and the aluminum-containing layer is heated to anneal the aluminum-containing layer as well as p-dope the bottom surface of the spheres. The diffusion of the p-type dopants also creates a back surface field in the spheres to improve efficiency. A dielectric layer is formed, and a phosphorus-containing layer is deposited over the spheres to dope the top surface n-type, forming a pn junction. The phosphorus layer is then removed. A conductor is deposited to contact the top surface. Conformal, index-graded lenses are then formed over each of the spheres to form a thin and flexible PV panel.
1 . A process for forming a solar cell structure comprising:
providing a substantially flat substrate containing aluminum;
depositing an aluminum-containing ink over the substrate, the aluminum-containing ink forming an uncured aluminum-containing layer;
depositing a plurality of semiconductor particles on the uncured aluminum-containing layer so that the particles are partially embedded in the aluminum-containing layer, the particles having a top surface portion for being exposed to the sun to generate electricity and having a bottom surface portion;
heating the aluminum-containing layer to diffuse p-type dopants into the bottom surface portion to create a back surface field, wherein the aluminum-containing layer is a conductor electrically contacting the bottom surface portion, wherein the semiconductor particles form a monolayer over the aluminum-containing layer;
depositing a dielectric layer over exposed portions of the aluminum-containing layer; and
depositing a conductor over the dielectric layer electrically contacting the top surface portion, the top surface portion being of an n-type,
wherein, at least after the step of depositing the conductor over the dielectric layer, the semiconductor particles are a plurality of diodes adapted to convert sunlight to electricity.
2 . The process of claim 1 wherein the semiconductor particles comprise silicon spheres, the process further comprising:
forming a mechanical bond where the aluminum-containing layer alloys with the silicon spheres, while creating a p+ region in the silicon spheres by: 1) diffusion of silicon from the silicon spheres into the aluminum-containing layer, and 2) aluminum diffusion from the aluminum-containing layer into the silicon spheres proximate to an interface of the silicon spheres and the aluminum-containing layer.
3 . The process of claim 1 wherein the semiconductor particles comprise silicon spheres and the aluminum-containing ink also contains silicon, the process further comprising:
forming a bond where the aluminum-containing layer alloys with the substrate by: 1) diffusion of silicon from the aluminum-containing ink into the substrate, and 2) diffusion of aluminum from the substrate into the aluminum-containing layer.
4 . The process of claim 1 where the substrate comprises an aluminum-containing foil.
5 . The structure of claim 1 where the substrate comprises at least one of aluminum, silicon, steel, copper, or brass.
6 . The process of claim 1 wherein the semiconductor particles comprise silicon spheres, wherein the aluminum-containing ink is coated on a moving substrate, and wherein the silicon spheres are subsequently coated on the moving substrate on top of the aluminum-containing layer.
7 . The process of claim 1 wherein the semiconductor particles comprise silicon spheres, wherein a bottom of the silicon spheres opposing the substrate is p-type, the method further comprising doping at least a top surface of the silicon spheres n-type subsequent to the step of depositing a dielectric layer over exposed portions of the aluminum-containing layer.
8 . The process of claim 1 wherein the semiconductor particles comprise silicon spheres, wherein the silicon spheres have an average diameter less than 300 microns.
9 . The process of claim 1 wherein all steps are performed under atmospheric pressures.