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Photovoltaic modules comprise solar cells having doped domains of opposite polarities along the rear side of the cells. The doped domains can be located within openings through a dielectric passivation layer. In some embodiments, the solar cells are formed from thin silicon foils. Doped domains can

Photovoltaic modules comprise solar cells having doped domains of opposite polarities along the rear side of the cells. The doped domains can be located within openings through a dielectric passivation layer. In some embodiments, the solar cells are formed from thin silicon foils. Doped domains can be formed by printing inks along the rear surface of the semiconducting sheets. The dopant inks can comprise nanoparticles having the desired dopant.

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1. A method for forming a doped semiconductor structure, the method comprising: printing a dopant ink in a pattern onto a first surface of a semiconductor sheet comprising silicon, wherein the dopant ink comprises doped silicon nanoparticles having an average primary particle diameter of no more tha

1. A method for forming a doped semiconductor structure, the method comprising: printing a dopant ink in a pattern onto a first surface of a semiconductor sheet comprising silicon, wherein the dopant ink comprises doped silicon nanoparticles having an average primary particle diameter of no more than about 100 nm; andforming a first doped contact localized in a region along the semiconductor surface by heating the doped silicon nanoparticles patterned on the semiconductor surface, wherein dopant from the printed ink patterned on the first surface of the semiconductor is driven into the semiconductor sheet during the heating and the doped silicon nanoparticles are incorporated into the first doped contact having a doped silicon structure extending into the semiconductor sheet and protruding as a local structure above the semiconductor sheet. 2. The method of claim 1 wherein the printing comprises inkjet printing. 3. The method of claim 2 wherein the ink has viscosity from about 0.1 mPa·s to about 100 mPa·s. 4. The method of claim 1 wherein the ink comprises no more than about 20 weight percent doped silicon nanoparticles. 5. The method of claim 1 wherein the heating comprises heating in an oven. 6. The method of claim 1 wherein the heating comprises rastering a laser over the printed pattern. 7. The method of claim 1 wherein the ink comprises a dopant composition in addition to the doped silicon nanoparticles. 8. The method of claim 1 further comprising: patterning a first metal current collector having contact with at least a portion of the first doped contact to form an electrical conduction path from the semiconductor sheet through the first doped contact into the current collector. 9. The method of claim 8 further comprising, before patterning the metal contact, forming a passivation layer comprising a dielectric material over the semiconductor substrate. 10. The method of claim 1 wherein the semiconductor substrate further comprises a second doped contact on the first surface of the semiconductor sheet, wherein the second doped contact comprises doped silicon and wherein the doped silicon nanoparticles incorporated into the first doped contact comprise an n-type dopant and the second doped contact comprises a p-type dopant. 11. The method of claim 1 wherein the first doped domain extends less than about 1 micron from the first surface of the semiconductor sheet. 12. The method of claim 1 wherein the doped silicon nanoparticles incorporated into the first doped contact have an average secondary particle size that is no more than four times the average primary particle size. 13. The method of claim 1 wherein the silicon particles have a dopant concentration of from about 1.0×10−7 atomic percent to about 15 atomic percent relative to the silicon atoms. 14. The method of claim 1 wherein the semiconductor sheet comprises crystalline silicon. 15. The method of claim 1 wherein the semiconductor sheet has a thickness of no more than about 250 microns.