HIGH-EFFICIENCY PHOTOVOLTAIC BACK-CONTACT SOLAR CELL STRUCTURES AND MANUFACTURING METHODS USING SEMICONDUCTOR WAFERS
A back contact back junction solar cell using semiconductor wafers and methods for manufacturing are provided. The back contact back junction solar cell comprises a semiconductor wafer having a doped base region, a light capturing frontside surface, and a doped backside emitter region. A frontside and backside dielectric layer and passivation layer provide enhance light trapping and internal reflection. Backside base and emitter contacts are connected to metal interconnects forming a metallization pattern of interdigitated fingers and busbars on the backside of the solar cell.
1 . A back contact back junction thin solar cell, comprising:
a semiconductor wafer with a thickness in the range of 50 to 250 microns, comprising:
a doped base region,
a light capturing frontside surface, and
a doped backside emitter region with a doping polarity opposite said doped base region;
a frontside dielectric layer on said frontside surface and a backside dielectric layer on said backside emitter region;
a frontside passivation layer on said frontside dielectric layer;
a backside passivation layer on said backside dielectric layer; wherein said backside passivation dielectric layer and said backside dielectric layer form a mirror; and
backside emitter contacts and backside base contacts connected to emitter regions and base regions through laser ablated contact openings in said backside passivation layer and said backside dielectric layer, said backside emitter contacts and backside base contacts connected to metal interconnects forming a metallization pattern of interdigitated fingers and busbars on the backside of said back contact back junction thin solar cell.
2 . The back contact back junction thin solar cell of claim 1 , wherein said doped backside emitter region is an epitaxial emitter region.
3 . The back contact back junction thin solar cell of claim 1 , wherein said doped backside emitter region is an epitaxial in-situ doped emitter region.
4 . The back contact back junction thin solar cell of claim 1 , wherein said frontside dielectric layer and said backside dielectric layer are thermal oxide layers.
5 . The back contact back junction thin solar cell of claim 1 , further comprising a permanent backside grid-shaped support reinforcement.
6 . The back contact back junction thin solar cell of claim 1 , wherein said metallization pattern of interdigitated fingers and busbars is a distributed busbar array.
7 . The back contact back junction thin solar cell of claim 1 , wherein the passivation layers comprise a thin silicon nitride layer.
8 . The back contact back junction thin solar cell of claim 1 , wherein the passivation layers comprise a thin aluminum oxide layer.
9 . A method for the manufacture of a back contact back junction thin solar cell from a doped crystalline semiconductor wafer, said wafer comprising a frontside and backside, the method comprising:
texturing said wafer frontside;
depositing an epitaxial emitter region on said wafer backside;
depositing a surface passivation layer on said wafer frontside and said wafer backside;
forming interdigitated emitter and base contact openings in said wafer backside surface passivation layer by laser ablation of the wafer backside surface passivation layer with a pulsed picosecond laser;
doping the interdigitated pattern of said emitter and base contact openings to form emitter regions and base regions; and
metalizing the cell backside to form backside base and emitter contacts in the pattern of interdigitated fingers and busbars.
10 . The method of claim 9 , wherein said epitaxial emitter region is in-situ doped with a thickness in the range of 0.5 to 5 microns.
11 . The method of claim 9 , wherein said surface passivation layer comprises a thermally grown oxide layer and a silicon nitride layer.
12 . The method of claim 9 , wherein said surface passivation layer comprises a thermally grown oxide layer and an LPCVD silicon nitride layer.
13 . The method of claim 9 , wherein said surface passivation layer comprises a thermally grown oxide layer and a PECVD silicon nitride layer.
14 . The method of claim 9 , wherein said surface passivation layer comprises a thermally grown oxide layer and an aluminum oxide layer.
15 . The method of claim 9 , wherein said step of doping the interdigitated pattern of said emitter and base contact openings to form emitter regions and base regions uses an inkjet printer to print silicon nano-particle inks on said interdigitated pattern of said emitter and base contact openings.
16 . The method of claim 9 , further comprising the step of printing said wafer frontside and backside with an undoped silicon nano-particle ink using an inkjet printer and sintering of said ink to texture said wafer frontside and backside.
17 . The method of claim 9 , wherein said metallization contacts comprise layers of nickel and silver.
18 . The method of claim 9 , wherein said metallization contacts comprise layers formed by aluminum ink.
19 . A back contact back junction thin solar cell, comprising:
semiconductor wafer with a thickness in the range of 50 to 250 microns, comprising:
a doped base region,
a light capturing frontside surface, and
a doped backside emitter region with a doping polarity opposite said doped base region;
a frontside first dielectric layer on said frontside surface and a backside first dielectric layer on said backside emitter region;
a frontside second dielectric layer on said frontside first dielectric layer, the combination serving as frontside passivation layer;
a backside second dielectric layer on said first backside dielectric layer, the combination serving as backside passivation layer;
wherein said backside first and second dielectric layers form a dielectric mirror;
backside emitter contacts and backside base contacts connected to emitter regions and base regions through contact openings in said backside first and second dielectric layers, said backside emitter contacts and backside base contacts connected to metal interconnects forming a metallization pattern of interdigitated fingers and busbars on the backside of said back contact back junction thin solar cell; and
at least one permanent support reinforcement positioned on the frontside or backside of said back contact back junction thin solar cell.
20 . The back contact back junction solar cell of claim 19 , wherein said contact openings are formed by pulsed laser ablation.
21 . The back contact back junction solar cell of claim 19 , wherein said contact openings are formed by sub-nanosecond-pulse duration pulsed-laser ablation.