Contact fabrication of emitter wrap-through back contact silicon solar cells
Back contact solar cells including rear surface structures and methods for making same. The rear surface has small contact areas through at least one dielectric layer, including but not limited to a passivation layer, a nitride layer, a diffusion barrier, and/or a metallization barrier. The dielectric layer is preferably screen printed. Large grid areas overlay the dielectric layer. The methods provide for increasing efficiency by minimizing p-type contact areas and maximizing n-type doped regions on the rear surface of a p-type substrate.
1. A method of making a back-contact solar cell, the method comprising the steps of:
forming a plurality of holes extending from a front surface of a semiconductor substrate to a rear surface of the substrate, the substrate comprising having a first conductivity type;
depositing a patterned diffusion barrier on the rear surface;
forming a diffusion zone on the front surface, regions of the rear surface not covered by the diffusion barrier, and on surfaces enclosing the holes, wherein the diffusion zone has a second conductivity type opposite to that of the first conductivity type;
disposing a first conductive grid on the diffusion barrier in electrical contact with the substrate in a subset of the regions of the rear surface not covered by the diffusion barrier; and
disposing a second conductive grid on the rear surface in electrical contact with the diffusion zone.
2. The method of claim 1 further comprising the step of changing the conductivity type of the subset of the regions substantially to the first conductivity type.
3. The method of claim 1 wherein the depositing step comprises using screen printing.
4. The method of claim 1 wherein the first conductive grid comprises aluminum.
5. The method of claim 1 wherein material comprising the second conductive grid at least partially fills the holes.
6. The method of claim 1 wherein a width of a grid line of the first conductive grid is wider than a width of one of the regions.
7. The method of claim 1 wherein the first conductive grid is interdigitated with the second conductive grid.
8. The method of claim 1 wherein at least one of the first conductive grid or the second conductive grid comprise grid lines having a tapered width.