Laser-Crystallised Thin-Film Polycrystalline Silicon Solar Cells - PowerPoint PPT Presentation

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

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

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

1. Introduction GTM Research

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

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

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

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

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

5. Grain structure Many Σ 3 twin boundaries  Defect density < 5e7 cm -2  Mobility of 300-450 at ~1e16 cm -3  30 nm Optical microscope TEM

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

7. Light IV

8. Improvement path Record Efficiency [%] 10 11 12 6 7 8 9 Jul-2011 Oct-2011 Jan-2012 Apr-2012 Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul-2013

8. Improvement path Record Efficiency [%] 10 11 12 6 7 8 9 Jul-2011 First devices with SiO x IL Oct-2011 Jan-2012 Apr-2012 Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul-2013

8. Improvement path Record Efficiency [%] 10 11 12 6 7 8 9 Jul-2011 First devices with SiO x IL Oct-2011 SiO x /SiC x / SiO x IL Jan-2012 Apr-2012 Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul-2013

8. Improvement path Record Efficiency [%] 10 11 12 6 7 8 9 Jul-2011 First devices with SiO x IL Oct-2011 SiO x /SiC x / SiO x IL Jan-2012 Apr-2012 SiO x IL SiO x /SiN x / Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul-2013

8. Improvement path 12 First devices with SiO x IL 11 SiO x /SiN x / Record Efficiency [%] SiO x IL 10 SiO x /SiC x / SiO x IL 9 improved 8 SiO x /SiN x / SiO x IL; 7 Rear texture 6 Jul-2011 Oct-2011 Jan-2012 Apr-2012 Jul-2012 Oct-2012 Jan-2013 Apr-2013 Jul-2013

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

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

11. Materials of Interest  SiC x  SiN x  SiO x  Layers deposited by RF sputtering or PECVD  10-200 nm thick  Either alone or in stacks

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

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

13. Wetting and crystallisation Int. layer Process range  Laser energy 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

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

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

15. Dopant source  Uniform region created during molten phase  p+ region at interface? 1.E+20 1.E+19 B conc. (cm-3) 80nm SiOx lowly doped 1.E+18 Si marker (arbitrary units) 1.E+17 IL/Glass 1.E+16 Silicon 1.E+15 6 7 8 9 Depth (µm)

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

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

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  1000.0 Sheet conductance (mS) 100.0 10.0 1.0 0.1 No IL SiOx SiOx SiOx SiNx SiCx SiCx (10nm) (80nm) (200nm) (80nm) (14nm) (140nm)

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+18 1.E+18 Crystal grain, no IL Grain boundary, no IL Fe conc. (cm-3) Fe conc. (cm-3) Fe conc. (cm-3) 1.E+17 1.E+17 1.E+17 Grain boundary, SiOx IL 1.E+16 1.E+16 1.E+16 1.E+15 1.E+15 1.E+15 IL/Glass IL/Glass IL/Glass 1.E+14 1.E+14 1.E+14 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 9 9 9 Depth (µm) Depth (µm) Depth (µm) 32

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

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 80nm SiN x 140nm SiC x 80nm SiO x 14nm SiC x No IL

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 

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

21. Transparent ARC 80 SiCx (47 nm, n=2.9) SiCx (14 nm, n=2.9) Absorption (%) 60 SiNx (80 nm, n=2.1) SiOx (70 nm, n=1.5) 40 BSG (n=1.5) 20 0 300 500 700 900 1100 Wavelength (nm)

22. Transparent ARC 80 SiCx (47 nm, n=2.9) SiCx (14 nm, n=2.9) Absorption (%) 60 SiNx (80 nm, n=2.1) SiOx (70 nm, n=1.5) 40 BSG (n=1.5) SiNx (50 nm reactively sputtered , n=2.0) 20 0 300 500 700 900 1100 Wavelength (nm)

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

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

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

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

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

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

26. Passivation Layer

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

27. Stability J SC V OC FF η mA/cm 2 mV % % Baked 27.6 585 72.4 11.7

27. Stability J SC V OC FF η mA/cm 2 mV % % Baked 27.6 585 72.4 11.7 Degraded 27.7 572 62.9 10.0