Silicon heterojunction solar cells
Methods are described for fabricating HIT solar cells, including double heterojunction and hybrid heterojunction-homojunction solar cells, with very thin single crystal silicon wafers, where the silicon wafer may be less than 80 microns thick, and even less than 50 microns thick. The methods overcome potential issues with handling these very thin wafers by using a process including epitaxial silicon deposition on a growth substrate, partial cell fabrication, attachment to a support substrate and then separation from the growth substrate. Some embodiments of the present invention may include a solar cell device architecture comprising the combination of a heterostructure on the front side of the device with a homojunction at the rear of the device. Furthermore, device performance may be enhanced by including a dielectric stack on the backside of the device for reflecting long wavelength infrared radiation.
1. A method of manufacturing a silicon heterojunction-homojunction solar cell, comprising:
providing a single crystal silicon substrate with a porous silicon separation layer on the surface thereof;
epitaxially depositing a highly doped single crystal silicon layer doped with a dopant of a first polarity on the surface of the porous silicon separation layer;
epitaxially depositing a doped single crystal silicon absorber layer doped with a dopant of said first polarity over said highly doped single crystal silicon layer, said highly doped single crystal silicon layer having a lower resistivity than said doped single crystal silicon absorber layer;
depositing a layer of intrinsic wide band gap material with a band gap larger than single crystal silicon over said doped single crystal silicon absorber layer;
depositing a layer of doped wide band gap material with a dopant of a second polarity with a band gap larger than single crystal silicon over said layer of intrinsic wide band gap material, said second polarity being opposite to said first polarity;
depositing a transparent conducting oxide layer over said layer of doped wide band gap material;
depositing front side electrical contacts on said transparent conducting oxide layer;
after said depositing front side electrical contacts, bonding the stack formed on said single crystal silicon substrate to an optically transparent substrate using an encapsulant;
separating said single crystal silicon substrate from said highly doped single crystal silicon layer at the porous silicon separation layer; and
forming an electrical contact to said highly doped single crystal silicon layer.
2. The method of claim 1 , further comprising, after said separating and before said forming:
depositing a dielectric stack on said highly doped single crystal silicon layer; and
forming apertures within said dielectric stack.
3. The method of claim 1 , wherein the wide band gap material is amorphous silicon.
4. The method of claim 1 , wherein said highly doped single crystal silicon layer has a resistivity of less than 10 −2 Ohm-cm.
5. The method of claim 1 , wherein said doped single crystal silicon absorber layer has a resistivity in the range of 1 to 5 Ohm-cm.
6. The method of claim 1 , wherein said doped single crystal silicon absorber layer has a thickness of less than 50 microns.
7. The method of claim 1 , wherein said doped single crystal silicon absorber layer has a thickness of less than 80 microns.
8. The method of claim 1 , further comprising, after said separating and before said forming, depositing a dielectric passivation layer on said highly doped single crystal silicon layer.
9. The method of claim 1 , wherein said highly doped single crystal silicon layer has a thickness of less than 5 microns.
10. The method of claim 1 , wherein said dopant of a first polarity is an n-type dopant and said dopant of a second polarity is a p-type dopant.
11. The method of claim 1 , wherein the wide band gap material is silicon carbide.
12. A method of manufacturing a silicon double heterojunction solar cell comprising:
providing a single crystal silicon substrate with a porous silicon separation layer on the surface thereof;
epitaxially depositing a doped single crystal silicon layer doped with a dopant of a first polarity on the surface of the porous silicon separation layer;
depositing a layer of intrinsic wide band gap material with a band gap larger than single crystal silicon over said doped single crystal silicon absorber layer;
depositing a layer of doped wide band gap material with a dopant of a second polarity with a band gap larger than single crystal silicon over said layer of intrinsic wide band gap material, said second polarity being opposite to said first polarity;
depositing a transparent conducting oxide layer over said layer of doped wide band gap material;
depositing front side electrical contacts on said transparent conducting oxide layer;
after said depositing front side electrical contacts, bonding the stack formed on said single crystal silicon substrate to an optically transparent substrate using an encapsulant;
separating said single crystal silicon substrate from said doped single crystal silicon absorber layer at the porous silicon separation layer;
depositing a second layer of intrinsic wide band gap material with a band gap larger than single crystal silicon over said doped single crystal silicon absorber layer;
depositing a second layer of doped wide band gap material with a dopant of a first polarity with a band gap larger than single crystal silicon over said second layer of intrinsic wide band gap material;
depositing a second transparent conducting oxide layer over said second layer of doped wide band gap material; and
depositing back-side electrical contacts on said second transparent conducting oxide layer.
13. The method of claim 12 , wherein said doped single crystal silicon absorber layer has a resistivity in the range of 1 to 5 Ohm-cm.
14. The method of claim 12 , wherein said doped single crystal silicon absorber layer has a thickness of less than 50 microns.
15. The method of claim 12 , wherein said doped single crystal silicon absorber layer has a thickness of less than 80 microns.
16. The method of claim 12 , wherein said dopant of a first polarity is an n-type dopant and said dopant of a second polarity is a p-type dopant.
17. The method of claim 12 , wherein the wide band gap material is amorphous silicon.
18. The method of claim 12 , wherein the wide band gap material is silicon carbide.