Efficient Black Silicon Photovoltaic Devices With Enhanced Blue Response

• US 20130340824A1
• Filed: 03/08/2011
• Published: 12/26/2013
• Est. Priority Date: 03/08/2011
• Status: Active Grant

• Current Assignee: Alliance For Sustainable Energy LLC
• Original Assignee: Alliance For Sustainable Energy LLC
• Inventors: Branz, Howard M., Oh, Jihun, Yuan, Hao-Chih
• Granted Patent: US 11,251,318 B2
• Time in Patent Office: Days
• US Class Current: 136/256
• CPC Class Codes: H01L 31/02168 the coatings being antireflective or having enhancing optical properties for the solar cells
• CPC Class Codes: H01L 31/02363 of the semiconductor body itself, e.g. textured active layers
• CPC Class Codes: H01L 31/0284 comprising porous silicon as part of the active layer(s) porous silicon as antireflective layer for photodiodes H01L31/0216; for solar cells H01L31/02168
• CPC Class Codes: H01L 31/1868 Passivation
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

A photovoltaic (PV) device with improved blue response. The PV device includes a silicon substrate with an emitter layer on a light receiving side. The emitter layer has a low opant level such that it has sheet resistance of 90 to 170 ohm/sq. Anti-reflection in the PV device is provided solely by a nano-structured or black silicon surface on the light-receiving surface, through which the emitter is formed by diffusion. The nano structures of the black silicon are formed in a manner that does not result in gold or another high-recombination metal being left in the black silicon such as with metal-assisted etching using silver. The black silicon is further processed to widen these pores so as to provide larger nanostructures with lateral dimensions in the range of 65 to 150 nanometers so as to reduce surface area and also to etch away a highly doped portion of the emitter.

Claims

1. A photovoltaic device with enhanced blue response, comprising:

a silicon substrate;

an emitter layer on a side of the silicon substrate, the emitter layer having a dopant level providing a sheet resistance of at least 90 ohms/sq; and

an antireflective surface on the emitter layer comprising black silicon.

2. The photovoltaic device of claim 1, wherein the emitter layer has a sheet resistance in the range of 90 to 170 ohm/sq.

3. The photovoltaic device of claim 1, wherein the black silicon has lateral structures dimensions in the range of 65 to 200 nanometers.

4. The photovoltaic device of claim 3, wherein the lateral structure dimensions are pore diameters of the black silicon or are outer diameters of pillars of the black silicon.

5. The photovoltaic device of claim 1, wherein the black silicon is free of gold.

6. The photovoltaic device of claim 1, wherein the black silicon comprises silver or copper and wherein the silver or the copper is at levels less than 10¹⁹ cm⁻

3.

7. The photovoltaic device of claim 1, wherein the photovoltaic device is a solar cell further comprising a passivation layer over the antireflective surface, a back electrical contact on a side of the silicon substrate opposite the side with the emitter layer, and a front electrical contact abutting the emitter layer through the passivation layer.

8. The photovoltaic device of claim 7, wherein the passivation layer comprises aluminum oxide or silicon oxide.

14. The photovoltaic device of claim 8, wherein the photovoltaic device has an internal quantum efficiency at 400 nm of greater than about 60 percent.

9. A photovoltaic device, comprising:

a silicon wafer with a back surface and a front, light-receiving surface;

a layer of black silicon, on the front, light-receiving surface, comprising a plurality of nanostructures with lateral structure dimensions greater than 65 nanometers; and

an emitter comprising dopant diffused a depth into the front, light-receiving surface through and beyond the layer of the black silicon, wherein a maximum level of the dopant is less than about 3×

10²¹ cm<sup>−

3</sup>.

10. The photovoltaic device of claim 9, wherein the layer of black silicon is substantially free of high-recombination metal particles.

11. The photovoltaic device of claim 9, wherein the level of the dopant is in a range such that the emitter has a sheet resistance of 90 to 170 ohm/sq.

12. The photovoltaic device of claim 11, further comprising front contacts on the front, light-receiving surface, wherein a zone underneath the front contacts is doped to a level exceeding the level of dopant in the emitter, whereby the photovoltaic device is a selective emitter black silicon device.

13. The photovoltaic device of claim 9, wherein the lateral structure dimensions are in the range of 80 to 150 nanometers and the structures have a depth or height of less than about 500 nanometers.

15. A method of fabricating photovoltaic devices, comprising:

forming black silicon on a surface of a silicon substrate;

forming an emitter in the silicon substrate by diffusing a dopant into the black silicon surface;

processing the silicon substrate to remove an outer layer of the black silicon surface to remove a volume of highly doped silicon;

forming a surface passivation coating on the black silicon surface; and

attaching front and back electrical contacts to the silicon substrate.

16. The method claim 15, wherein after the processing of the silicon substrate to remove the outer layer, the emitter has a dopant level providing a sheet resistance of at least about 90 ohm/sq.

17. The method of claim 15, wherein the processing of the silicon substrate to remove the outer layer includes increasing lateral structure dimensions of nanostructures in the black silicon surface to a range of 65 to 200 nanometers.

18. The method of claim 15, wherein the processing of the silicon substrate to remove the outer layer includes etching the black silicon surface with at least one of TMAH, KOH, NaOH, HF, and HNO₃ for a period of time.

19. The method of claim 18, wherein the etching period of time is at least about 10 seconds.

20. The method of claim 15, wherein the forming of the black silicon on the surface of the silicon substrate comprises metal-assisted etching.

21. The method of claim 20, wherein the metal-assisted etching is performed using nanoparticles formed from a non-high-recombination metal.

22. The method of claim 21, wherein the metal-assisted etching is performed using silver or copper nanoparticles.

23. A method of making a photovoltaic device, comprising:

forming a black silicon layer comprising nanostructures on a surface of a silicon substrate;

processing the surface of the silicon substrate to remove an outer portion of the black silicon layer to increase the lateral structure dimensions of the nanostructures;

forming an emitter in the silicon substrate by diffusing a dopant into the black silicon layer; and

forming a surface passivation coating on the black silicon layer.

24. The method of claim 23, wherein the processing of the surface of the silicon substrate to remove the outer portion includes etching with a solution including at least one of TMAH, KOH, NaOH, HF, and HNO₃.

25. The method of claim 23, wherein the processing of the surface of the silicon substrate to remove the outer portion includes increasing average lateral structure dimensions of the nanostructures in the black silicon layer to a range of 65 to 200 nanometers.

26. The method of claim 23, wherein the forming of the black silicon layer comprises metal-assisting etching with silver or copper nanoparticles.

27. The method of claim 23, wherein the emitter has a dopant level providing a sheet resistance of at least about 90 ohm/sq.

28. A method of fabricating a photovoltaic device, comprising:

forming black silicon on a surface of a silicon wafer; and

forming an emitter in the surface of the silicon wafer including diffusing a dopant into the black silicon,

wherein the forming of the black silicon includes increasing average lateral structure dimensions of nanostructures in the black silicon to a range of 65 to 200 nanometers, and

wherein the emitter has a dopant level providing a sheet resistance of at least about 90 ohm/sq.