Laser-Crystallised Thin-Film Polycrystalline Silicon Solar Cells. Jonathon Dore SPREE Research Seminar - 27th June, 2013

Transcription

1 Laser-Crystallised Thin-Film Polycrystalline Silicon Solar Cells Jonathon Dore SPREE Research Seminar - 27th June, 2013

2 Contents Introduction motivation for thin-film Thin-film PV technologies Diode laser crystallised thin-film pc-si Material and device preparation Intermediate layers Stability Other current work Near-term priorities for future work Long-term priorities for future work

3 Contents Introduction motivation for thin-film Thin-film PV technologies Diode laser crystallised thin-film pc-si Material and device preparation Intermediate layers Stability Other current work Near-term priorities for future work Long-term priorities for future work

4 1. Introduction GTM Research

5 Contents Introduction motivation for thin-film Thin-film PV technologies Diode laser crystallised thin-film pc-si Material and device preparation Intermediate layers Stability Other current work Near-term priorities for future work Long-term priorities for future work

6 2. Thin-Film PV Technologies Commercial CdTe CIGS a-si/µc-si Research CZTS OPV Thin crystalline silicon Wafer transfer Thin polycrystalline

7 3. Thin Polycrystalline Si Solid Phase SPC AIC Liquid Phase ZMR EBC LC UV Visible IR

8 Contents Introduction motivation for thin-film Thin-film PV technologies Diode laser crystallised thin-film pc-si Material and device preparation Intermediate layers Stability Other current work Near-term priorities for future work Long-term priorities for future work

9 Contents Introduction motivation for thin-film Thin-film PV technologies Diode laser crystallised thin-film pc-si Material and device preparation Intermediate layers Stability Other current work Near-term priorities for future work Long-term priorities for future work

10 4. Material Preparation 808 nm CW LIMO diode laser 12 mm x 170 µm H H H H H H diffused n+ undoped p- poly-si a-si B-doped Intermediate layer ~10 µm ~150 nm Glass 5x5 cm 2 3 mm

11 5. Grain structure Many Σ3 twin boundaries Defect density < 5e7 cm -2 Mobility of at ~1e16 cm nm Optical microscope TEM

12 6. Device Fabrication n contact pad Aluminium Resist n+ p- p contact pad Cell area = 1 cm 2 Intermediate layer Glass

13 7. Light IV

14 Jul-2011 Oct-2011 Jan-2012 Apr-2012 Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul-2013 Record Efficiency [%] 8. Improvement path

15 Jul-2011 Oct-2011 Jan-2012 Apr-2012 Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul-2013 Record Efficiency [%] 8. Improvement path First devices with SiO x IL

16 Jul-2011 Oct-2011 Jan-2012 Apr-2012 Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul-2013 Record Efficiency [%] 8. Improvement path First devices with SiO x IL SiO x /SiC x / SiO x IL 8 7 6

17 Jul-2011 Oct-2011 Jan-2012 Apr-2012 Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul-2013 Record Efficiency [%] 8. Improvement path First devices with SiO x IL SiO x /SiC x / SiO x IL SiO x /SiN x / SiO x IL 7 6

18 Jul-2011 Oct-2011 Jan-2012 Apr-2012 Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul-2013 Record Efficiency [%] 8. Improvement path First devices with SiO x IL SiO x /SiC x / SiO x IL SiO x /SiN x / SiO x IL improved SiO x /SiN x / SiO x IL; Rear texture

19 Contents Introduction motivation for thin-film Thin-film PV technologies Diode laser crystallised thin-film pc-si Material and device preparation Intermediate layers Stability Other current work Near-term priorities for future work Long-term priorities for future work

20 10. Intermediate Layer n contact pad Aluminium Resist n+ p- p contact pad Cell area = 1 cm 2 Intermediate layer Glass

21 10. Intermediate Layer Wetting layer Dopant source Contamination barrier Stable > 1414C Transparent anti-reflection coating (ARC) Passivation layer Intermediate layer

22 11. Materials of Interest SiC x SiN x SiO x Layers deposited by RF sputtering or PECVD nm thick Either alone or in stacks

23 Intermediate Layer Wetting layer Dopant source Contamination barrier Stable > 1414C Transparent anti-reflection coating (ARC) Passivation layer Intermediate layer

24 12. Wetting and crystallisation Laser energy Int. layer Process range None 13 J/cm² SiO x 194 J/cm² SiN x 220 J/cm² SiO x /SiC x stack 246 J/cm² Too low (nc regions) Too high (dewetting) Just right

25 13. Wetting and crystallisation Laser energy Int. layer Process range None 13 J/cm² SiO x 194 J/cm² SiN x 220 J/cm² SiO x /SiC x stack 246 J/cm² SiN x layers result in pinholes in Si at high laser energies Transmission micrograph

26 Intermediate Layer Wetting layer Dopant source Contamination barrier Stable > 1414C Transparent anti-reflection coating (ARC) Passivation layer Intermediate layer

27 14. Dopant source undoped p- poly-si a-si B-doped Intermediate layer SiO x /SiN x /SiO x stack B B B B B B Glass 5x5 cm 2

28 B conc. (cm-3) 15. Dopant source Uniform region created during molten phase p+ region at interface? 1.E+20 1.E+19 1.E+18 1.E+17 1.E+16 80nm SiOx lowly doped Si marker (arbitrary units) IL/Glass 1.E+15 Silicon Depth (µm)

29 16. Dopant source p+ region at interface? Spreading resistance shows no p+ Inversion layer?

30 Intermediate Layer Wetting layer Dopant source Contamination barrier Stable > 1414C Transparent anti-reflection coating (ARC) Passivation layer Intermediate layer

31 Sheet conductance (ms) 17. Contamination Barrier Problem is blocking B from glass! SiO x best barrier Can use SiO x /SiC x or SiO x /SiN x stacks No IL SiOx (10nm) SiOx (80nm) SiOx (200nm) SiNx (80nm) SiCx (14nm) SiCx (140nm)

32 Fe conc. (cm-3) 18. Contamination Barrier Iron can also diffuse from glass Iron found at silicon grain boundary when no IL used No iron when SiOx IL used 1.E+18 1.E+17 1.E+16 Crystal grain, no IL Grain boundary, no IL Grain boundary, SiOx IL 1.E+15 1.E+14 IL/Glass Depth (µm) 32

33 Intermediate Layer Wetting layer Dopant source Contamination barrier Stable > 1414C Transparent anti-reflection coating (ARC) Passivation layer Intermediate layer

34 19. Stability Thick SiC x or SiN x layers cause wrinkling at the glass surface Visible in reflection micrographs at IL interface viewed through the glass 140nm SiC x 80nm SiN x 80nm SiO x 14nm SiC x No IL

35 20. Stability Nitrogen from SiN x layer diffuses into Si during crystallisation N conc in Si when SiC x and SiO x used likely from atmosphere No excess C from SiC x or O from SiO x

36 Intermediate Layer Wetting layer Dopant source Contamination barrier Stable > 1414C Transparent anti-reflection coating (ARC) Passivation layer Intermediate layer

37 Absorption (%) 21. Transparent ARC SiCx (47 nm, n=2.9) SiCx (14 nm, n=2.9) SiNx (80 nm, n=2.1) SiOx (70 nm, n=1.5) BSG (n=1.5) Wavelength (nm)

38 Absorption (%) 22. Transparent ARC SiCx (47 nm, n=2.9) SiCx (14 nm, n=2.9) SiNx (80 nm, n=2.1) SiOx (70 nm, n=1.5) BSG (n=1.5) SiNx (50 nm reactively sputtered, n=2.0) Wavelength (nm)

39 Intermediate Layer Wetting layer Dopant source Contamination barrier Stable > 1414C Transparent anti-reflection coating (ARC) Passivation layer Intermediate layer

40 23. Passivation Layer Single- and double-layer stacks Silicon IL Glass 80nm SiO x (n 1.5) 20 nm SiC x (n=2.9) 80nm SiO x 70 nm SiN x (n=2.1) 80nm SiO x

41 24. Passivation Layer Poor front surface for SiO x /SiC x

42 25. Passivation Layer triple-layer stacks 15 nm SiO x 20 nm SiC x 80nm SiO x 15 nm SiO x 70 nm SiN x 80nm SiO x

43 26. Passivation Layer Surface SiOx improves IQE ONO still not ideal

44 26. Passivation Layer Surface SiOx improves IQE ONO still not ideal Optimised ONO (with reactive sputtering) better

45 26. Passivation Layer

46 Contents Introduction motivation for thin-film Thin-film PV technologies Diode laser crystallised thin-film pc-si Material and device preparation Intermediate layers Stability Other current work Near-term priorities for future work Long-term priorities for future work

47 27. Stability J SC ma/cm 2 V OC mv FF % η % Baked

48 27. Stability J SC ma/cm 2 V OC mv FF % η % Baked Degraded

49 28. Stability Occurs in dark

50 28. Stability Occurs in dark Related to absorber doping Best stabilised efficiency = 10.4%

51 29. Selective p+ (Chaho Ahn) Degradation likely due to poor contact with lightly-doped absorber p- 10e16 cm -3

52 29. Selective p+ (Chaho Ahn) Degradation likely due to poor contact with lightly-doped absorber Solution: selective p+ under absorber contact p- 10e16 cm -3 p+

53 30. Selective p+ (Chaho Ahn) Cell Baseline (initial) Baseline (delayed) Selective p+ (initial) Selective p+ (delayed) J SC [ma/cm 2 ] V OC [mv] FF [%] η [%] Data for cells with SiO x intermediate layer

54 Contents Introduction motivation for thin-film Thin-film PV technologies Diode laser crystallised thin-film pc-si Material and device preparation Intermediate layers Stability Other current work Near-term priorities for future work Long-term priorities for future work

55 31. Rear Texture (Zamir Pakhuruddin)

56 32. Rear Texture (Zamir Pakhuruddin) AFM RMS = 78 nm Absorption without rear reflector or ARC

57 33. Rear Texture (Zamir Pakhuruddin)

58 33. Rear Texture (Zamir Pakhuruddin)

59 34. Suns-V OC Measured prior to metallisation Mostly n=1 recombination Measured after metallisation Significant R SH ~ 500 Ohms.cm 2 and n = 2 influence

60 35. Dark Lock-In Thermography DLIT shows hotspot at Si crack (shown for neighbouring cell) Same in forward and reverse bias Ohmic shunt

61 36. Crack-free crystallisation (Jialiang Huang) Standard process Crack-free process Scan direction 12 mm 12 mm

62 37. Grain orientation control (Jae Sung Yun) Standard Process 100 nm SiO x Capping Layer 111 Position Position 2 Position 3 Inverse pole orientation map

63 Sheet Resistance 38. Laser diffusion (Miga Jung) RTP diffusion Expensive Slow Causes glass softening Exacerbates cracks Large process window? Laser diffusion Cheap Fast No effect on glass No effect on cracks Process window? Sample Strip # RTA sample #1 RTA sample #2 Laser Diffused sample

64 Contents Introduction motivation for thin-film Thin-film PV technologies Diode laser crystallised thin-film pc-si Material and device preparation Intermediate layers Stability Other current work Near-term priorities for future work Long-term priorities for future work

65 39. Near-Term Priorities for Future Work Transfer processes to TETB Improve bulk passivation Improve surface passivation Identify and address device fabrication losses E.g. Cell isolation scribes Investigate alternative junction formation Heterojunction Other? Plasmonic light-trapping?

66 Contents Introduction motivation for thin-film Thin-film PV technologies Diode laser crystallised thin-film pc-si Material and device preparation Intermediate layers Stability Other current work Near-term priorities for future work Long-term priorities for future work

67 40. Simple economics * Multi wafer spot price = eff = 17% $0.20/W * BSG ~ $20/m² above standard eff = 12% $0.17/W * Need to increase eff and/or use standard glass

68 41. Process sequence Typical TF-Si Laser-crystallised TF-Si Clean Deposit Scribe Clean Deposit Scribe Deposit Scribe Module assembly Clean Deposit Crystallise Coat Diffuse Etch Hydrogenate Scribe Coat Bake Inkjet Etch Expose Bake Inkjet Clean Bake Clean Deposit Scribe Bake Module Assembly Need to simplify contacting scheme

69 Jul-2011 Oct-2011 Jan-2012 Apr-2012 Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul Conclusions Laser-crystallised poly-si solar cell reaching 11.7% efficiency Exceeds record for thin-film poly-si Short-term, recoverable degradation Selective p+ metallisation makes stable cells Performance improvements mostly due to intermediate layer Many more opportunities for further improvement