Point contacts for polysilicon emitter solar cell
The present invention relates to electrical contacts in a semiconductor device, and more particularly to methods and apparatuses for providing point contacts in a polysilicon emitter or HIT type solar cell. According to certain aspects, the invention uses a dielectric layer interposed between the substrate and a conductive layer to provide a limited area over which junction current can flow. The benefit is that the metal grid conductors do not need to align to the contacts, and can be applied freely without registration. Another benefit of the invention is that it provides increased efficiency for poly emitter and HIT cells through use of point contacts to increase current density. A further benefit is that patterning can be accomplished using low cost methods such as inclusion masking, screen printing or laser ablation. A still further benefit is that final contacts do not need alignment to the point contacts, eliminating registration required for conventional point contact designs.
1. A method of fabricating a solar cell comprising:
forming a conductive layer over a substrate, the conductive layer providing for junction current flow between the underlying substrate and overlying conductors;
forming a dielectric layer between the conductive layer and the substrate that restricts the junction current flow; and
forming a plurality of point contacts in the dielectric layer that enables the junction current flow through the dielectric layer,
wherein the step of forming the point contacts includes:
applying a resist layer that incorporates inclusions over the substrate; and
etching the dielectric layer, wherein the dielectric layer is etched predominately at the sites of the inclusions,
wherein the inclusions comprise aluminum particles.
2. A method according to claim 1 in which the inclusions dissociate in an etch bath.
3. A method according to claim 1 wherein the step of forming the point contacts includes patterning the point contacts using a laser.
4. A method according to claim 1 wherein the step of forming the point contacts is performed such that the dielectric layer with the point contacts formed therein covers more than 50% of the area between the substrate and the conducting layer.
5. A method according to claim 1 wherein the conductive layer comprises a transparent conductor.
6. A method according to claim 1 wherein the conductive layer comprises doped polysilicon.