Method and apparatus providing inline photoluminescence analysis of a photovoltaic device

1. A method of determining a processing characteristic of photovoltaic device fabrication, the method comprising:

receiving a substrate which has a chloride treated absorber layer thereon;

further processing the substrate having the chloride treated absorber layer;

illuminating the processed substrate with light of a predetermined wavelength;

determining the intensity of photoluminescent light produced by the processed substrate; and

forming a photoluminescent light intensity signature based on the intensity of the photoluminescent light,

wherein further processing the substrate comprises forming a back contact on the absorber layer, heat treating the back contact, and utilizing the intensity of the photoluminescent light to detect deviations in temperature during the heat treating of the back contact.

2. A method as in claim 1 , wherein the intensity of photoluminescent light is detected at a plurality of locations on the substrate.

3. A method as in claim 2 , further comprising:

comparing a photoluminescent light intensity signature for the substrate with a reference photoluminescent light intensity signature to characterize a processing condition of the further processed substrate.

4. A method as in claim 1 , wherein the light source produces red light.

5. A method as in claim 1 wherein the light source produces blue light.

6. A method as in claim 1 , wherein the light source produces green light.

7. A method as in claim 1 , further comprising moving the processed substrate relative to at least one photodetector which receives photoluminescent light from the processed substrate.

8. A method as in claim 7 , wherein the photodetector is stationary and the photovoltaic substrate is moved past the photodetector.

9. A method as in claim 1 , wherein further processing the substrate comprises doping the absorber layer and utilizing the intensity of the photoluminescent light to detect a doping concentration of the absorber layer.

10. A method as in claim 9 , wherein the doping comprises copper doping.

11. A method as in claim 2 , further comprising forming the light intensity signature by combining the detected photoluminescent light intensity from the plurality of locations.

12. A method as in claim 2 , wherein the plurality of locations are provided along the length and width of the substrate.

13. A method as in claim 1 , wherein the processed substrate is part of a completed photovoltaic device, the completed photovoltaic device being illuminated through the substrate by the light of the predetermined wavelength.

14. A method as in claim 13 , wherein the completed photovoltaic device includes scribe lines which define photovoltaic cells, the method further comprising identifying the location of the scribe lines and forming the photoluminescent light intensity signature based on a plurality of locations on the completed photovoltaic device, not including at the locations of the scribe lines.

15. A method as in claim 1 , wherein the predetermined wavelength is determined by at least one of the type of light source and a band-pass filter.

16. A method as in claim 1 , further comprising band-pass filtering the photoluminescent light before determining the intensity.

17. A method as in claim 1 , wherein the substrate comprises a CdS window layer and a CdTe absorber layer.

18. A method as in claim 1 , further comprising lines bias conditioning the substrate after completion of the further processing and wherein the substrate is illuminated after the bias conditioning.

19. A method as in claim 1 , further comprising lines bias conditioning the substrate after completion of the further processing and wherein the substrate is illuminated before the bias conditioning.

20. A method as in claim 1 , wherein the illumination and detecting are done in line in a photovoltaic device manufacturing line.

21. A method of inspecting a completed photovoltaic device comprising a heat treated back contact, the method comprising:

illuminating the photovoltaic device through a light receiving surface with light of a predetermined wavelength;

determining the intensity of photoluminescent light produced by the photovoltaic device;

forming a photoluminescent light intensity signature for the photovoltaic device,

utilizing the intensity of the photoluminescent light to detect deviations in temperature during heat treating of the back contact.

22. A method as in claim 21 , wherein the predetermined wavelength is a wavelength of red light.

23. A method as in claim 21 , wherein the predetermined wavelength is a wavelength of blue light.

24. A method as in claim 21 , wherein the predetermined wavelength is a wavelength of green light.

25. A method as in claim 21 , further comprising moving the completed photovoltaic device past a fixed tool containing a source of illumination and a photoluminescent detector.

26. A method as in claim 21 , further comprising using the light intensity signature to determine a parameter used in a process of fabricating the completed photovoltaic device.

27. A method as in claim 26 , wherein the parameter is a doping concentration of an absorber layer within the completed photovoltaic device.

28. A method as in claim 27 , wherein the doping concentration is a copper doping concentration.

29. A method as in claim 22 , wherein the intensity of the photoluminescent light is determined in the wavelength range of about 900 nm to about 1100 nm.

30. A method as in claim 23 , wherein the intensity of the photoluminescent light is determined in the wavelength range of about 650 nm to about 800 nm.