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Photonic crystals and related nanostructures for solar light management

Photonic crystals and related nanostructures for solar light management. Christian Seassal , Loïc Lalouat, He Ding, Romain Champory, Ngoc Vu Hoang, Abdelmounaim Harouri, Hai-Son Nguyen, Régis Orobtchouk, Alain Fave, Fabien Mandorlo, Emmanuel Drouard

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Photonic crystals and related nanostructures for solar light management

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  1. Photonic crystals and related nanostructures for solar light management Christian Seassal, Loïc Lalouat, He Ding, Romain Champory, Ngoc Vu Hoang, Abdelmounaim Harouri, Hai-Son Nguyen, Régis Orobtchouk, Alain Fave, Fabien Mandorlo, Emmanuel Drouard INL, Institut des Nanotechnologies de Lyon, UMR 5270 CNRS-Université de Lyon, Ecole Centrale de Lyon, INSA-Lyon, France In collaboration with: Imec (V. Depauw et al), LPICM (P. Roca i Cabarrocas et al), Obducat (K. Lee et al), LPN (S. Collin et al), ILM (A. Pereira et al), U.Namur (O. Deparis et al)

  2. Context: Bulk solar cells, thin film solar cells L’optique pour le photovoltaïque • Efficiency limitations • Si solarcell • Thin film solarcell • Which limitations? • In-couplinglosses R0? AR layer

  3. Context: Bulk solar cells, thin film solar cells Rough surface L’optique pour le photovoltaïque • Efficiency limitations • Si solarcell • Thin film solarcell • Which limitations? • In-couplinglosses • EQE/absorption limited in red/IR A100%?

  4. Context: Bulk solar cells, thin film solar cells L’optique pour le photovoltaïque • Efficiency limitations • Si solarcell • Thin film solarcell • Which limitations? • In-couplinglosses • EQE/absorption limited in red/IR • Thermalization in the UV/blue • No absorption belowEg Third Generation Photovoltaics, Vasilis Fthenakis Ed.

  5. Efficiency enhancement in PV devices L’optique pour le photovoltaïque • In-coupling and absorption control • Using the photonictoolbox: Samuelson U. Lund, 2015 wires/holes/ cones/pyramids Bermel MIT, 2007 Metal/dielectric F. J. Haug EPFL, JPV 2015 guided modes / localized modes Boriskina MIT, 2015

  6. Periodic photonic structures for energy harvesting L’optique pour le photovoltaïque • High index contrast periodic structures: • a platform for Photovoltaics U. Delaware INL INL GIST Wavelength-selective intermediate mirror High efficiency absorber Resonant wavelength converter Antireflecting structure AR “layer” Absorber (Si in this talk) Solar cells Back electrode/reflector

  7. Periodic photonic structures for energy harvesting L’optique pour le photovoltaïque • High index contrast periodic structures: • a platform for Photovoltaics U. Delaware INL INL GIST Wavelength-selective intermediate mirror High efficiency absorber Resonant wavelength converter Antireflecting structure AR “layer” Absorber (Si in this talk) Solar cells Back electrode/reflector

  8. Periodic photonic structures for energy harvesting L’optique pour le photovoltaïque • High index contrast periodic structures: • a platform for Photovoltaics U. Delaware INL INL GIST Wavelength-selective intermediate mirror High efficiency absorber Resonant wavelength converter Antireflecting structure RE-doped “layer” (AR+converter) Absorber (Si in this talk) Solar cells Back electrode/reflector

  9. Periodic photonic structures for energy harvesting L’optique pour le photovoltaïque • High index contrast periodic structures: • a platform for Photovoltaics U. Delaware INL INL GIST Wavelength-selective intermediate mirror High efficiency absorber Resonant wavelength converter Antireflecting structure AR “layer” Absorber (Si in this talk) Solar cells Back electrode/reflector

  10. Periodic photonic structures for energy harvesting L’optique pour le photovoltaïque • High index contrast periodic structures: • a platform for Photovoltaics U. Delaware INL INL GIST Wavelength-selective intermediate mirror High efficiency absorber Resonant wavelength converter Antireflecting structure AR “layer” Top junction Indermediate reflector Solar cells Bottom junction Back electrode/reflector

  11. How can nanophotonics outperform solar cells? L’optique pour le photovoltaïque Light traping into resonant modes Increased absorption Light localisation Higher absorption, lower pin thickness Radiative losses trapping (direct bandgap cells) • Increased Voc Control of absorption/emission of light, wavelength conversion • Solar cells using UV, IR photons • Increased Jsc • Increased angular acceptance

  12. Efficiency enhancement in PV devices L’optique pour le photovoltaïque • In-coupling and absorption control • Up to whichlimit? « Yablonovitch » limit, 4n² IEEE Trans. Electron. Dev. 1984 weaklyabsorbing medium Lambertianlimit, below 4n² M.A. Green weakly and stronglyabsorbing media

  13. Efficiency enhancement in PV devices L’optique pour le photovoltaïque • In-coupling and absorption control • Up to whichlimit? • Usingthe photonictoolbox

  14. Efficiency enhancement in PV devices L’optique pour le photovoltaïque • Key questions: Which are the best (nano)structures for PV? Optical, electricalproperties How to realizethese at lowcost? Whatis the mostappropriate absorber thickness Real performances of photonizedsolarcells

  15. Outline L’optique pour le photovoltaïque • Introduction: nanophotonics and solarenergy conversion • Photoniccrystals and solarcells • Physics and modal engineering, case of a-Si:H • Thin c-Si solarcellsassisted by PhCs • Multi-periodic/complexabsorbers • Absorption enhancementwith pseudo-disorderednanopatterns • Design rules for solarcellsincludingcomplex patterns • PhCs for wavelength conversion • Rare earthdopedphotonicmetastructures for down shifting • Conclusion and outlook

  16. Outline L’optique pour le photovoltaïque • Introduction: nanophotonics and solarenergy conversion • Photoniccrystals and solarcells • Physics and modal engineering, case of a-Si:H • Thin c-Si solarcellsassisted by PhCs • Multi-periodic/complexabsorbers • Absorption enhancementwith pseudo-disorderednanopatterns • Design rules for solarcellsincludingcomplex patterns • PhCs for wavelength conversion • Rare earthdopedphotonicmetastructures for down shifting • Conclusion and outlook

  17. 2-Photonic crystal absorbers • Case of an ultra-thin a-Si:H layer, 100nm • RCWA simulation: absorption spectrum PhC -a=380nm -D/a=0.62 Flat reference Y. Park, Opt. Express 17, 14321 (2009) G. Gomard et al., J. Appl. Phys. 108, 123102 (2010)

  18. 2-Photonic crystal absorbers • Case of an ultra-thin a-Si:H layer, 100nm • which mechanisms control the absorption? • For>550nm >80% PhC Flat reference PBG PBG R. Peretti et al., J. Appl. Phys. 111, 123114 (2012)

  19. 2-Photonic crystal absorbers • Case of an ultra-thin a-Si:H layer, 100nm • which mechanisms control the absorption? • For>550nm SNOM SEM (weakly) self-localized slow light mode

  20. 2-Photonic crystal absorbers • Case of an ultra-thin a-Si:H layer, 100nm • which mechanisms control the absorption? The absorbing medium Abs. coef.= The resonance = mediator Q0=wt0 • For>550nm • Absorption peaks due to Bloch mode resonances • Critical coupling of a single mode: 50% absorption • Additional absorption peaks = Multimode structure •  Abs. up to 100% Critical coupling conditions or For a-Si:H : a=1000cm-1 Q0=10-100 Y. Park, Opt. Express 17, 14321 (2009) R. Peretti et al., J. Appl. Phys. 111, 123114 (2012)

  21. 2-Photonic crystal absorbers • Case of a 100nm thick a-Si:H layer • which mechanisms control the absorption? • For 450nm • No absorption peak • but... strong absorption increase PhC Flat reference

  22. 2-Photonic crystal absorbers • Investigating the physics of absorbing PCs in the blue l-range SNOM experiments Back-side illumination Front-side collection using a SNOM tip FDTD simulations Incident light coupled to vertically guided “channeling modes” Ack.: R. Artinyan, S. Callard G. Gomard et al., APL 104, 051119 (2014)

  23. 2-Photonic crystal absorbers • Investigating the physics of absorbing PCs in the blue l-range FDTD simulations 70-85% of incident light coupled “channeling modes”, and absorbed in a-Si:H, but… etched sidewalls G. Gomard et al., APL 104, 051119 (2014)

  24. 2-Photonic crystals and solar cells • Case of a 1µm thick c-Si solar cell stack With periodic nano-pyramids Ful parameters scan: (os) 1. Period (Λ) 2. ff=a / Λ (Λ) 3. Thickness of optical spacer (os)

  25. 2-Photonic crystals and solar cells • Case of a 1µm thick c-Si solar cell stack Period (Λ): 800 nm, ff: 0.85 Optical spacer (os): 110nm Anti-Reflection Effect More modes: e.g. SBM 23.59 mA/cm² 11.52 mA/cm² • 105% increase

  26. 2-Photonic crystals and solar cells • Nanopattern shape optimization: optical assessment Collab.: imec, U. Namur, LPICM, Obducat

  27. 2-Photonic crystals and solar cells • Optimized nanopattern: optical assessment, experiments 1µm thick c-Si “Epifree silicon” • Over the Lambertian limit for l>500nm • Over the 4n² limit for specific resonances Collab.: imec, U. Namur, LPICM, Obducat

  28. 2-Photonic crystals and solar cells Nanopattern shape optimization: electrical properties • 280-µm-thick FZ p-type wafers, patterned by Nanoimprint, passivated with a-Si:H • Carrier lifetime assessment by Quasi Steady-State PhotoConductance Flat wafer RIE shallow RIE deep ICP TMAH 780 µs 170 µs 44 µs 2200 µs 930 µs • Lifetimes affected by: • The etching process: wet better than dry • Surface area enhancement + conformalityof passivating layer Collab.: imec, U. Namur, LPICM, Obducat

  29. 2-Photonic crystals and solar cells Solar cells, 1µm thick c-Si with periodic nanopatterns 4.5% Collab.: imec, U. Namur, LPICM, Obducat

  30. 2-Photonic crystals and solar cells Solar cells, 1µm thick c-Si with periodic nanopatterns 6.5% efficiency, 18mA/cm² 4.5% • Strong Jsc increase due to photonic crystals • Still room for improvement to reach simulated Jsc : parasitic absorption

  31. 2-Photonic crystals and solar cells Using c-Si prepared by PECVD (LPICM) low cost low T° scalable Collab.: LPICM, LPN, Total • Nanopatterning of PECVD c-Si is feasible Nano Lett 2016, to appear

  32. 2-Photonic crystals and solar cells Using c-Si prepared by PECVD (LPICM) low cost low T° scalable Collab.: LPICM, LPN, Total • Still limited efficiency due to absorption in front and back contacts, and limited absorption in IR Nano Lett 2016, to appear

  33. 2-Photonic crystals and solar cells How to further increase the efficiency/get closer to the limits? K.X. Wang Stanford, Nano Lett. 2012 X.Q. Meng U. Lyon, Opt. Express 2012 U.W. Paetzold, Jülich, APL 2014 S. Noda U. Kyoto, ACS Phot 2014 • Dual gratings • Periodic  controlled disorder  disorder

  34. Outline L’optique pour le photovoltaïque • Introduction: nanophotonics and solarenergy conversion • Photoniccrystals and solarcells • Physics and modal engineering, case of a-Si:H • Thin c-Si solarcellsassisted by PhCs • Multi-periodic/complexabsorbers • Absorption enhancementwith pseudo-disorderednanopatterns • Design rules for solarcellsincludingcomplex patterns • PhCs for wavelength conversion • Rare earthdopedphotonicmetastructures for down shifting • Conclusion and outlook

  35. 3-Multi-periodic/complex absorbers • What can we expect from disorder? SNOM SEM (weakly) self-localized slow light mode Strongly localized light High confinement in real space. Impact in a solar cell?

  36. 3-Multi-periodic/complex absorbers • Increasing the absorption bandwidth in the low absorption domain Pseudo-disordered pattern = supercell of randomly located holes, periodically repeated in a square lattice. L. Lalouat et al., SOLMAT (2016) H. Ding et al., Opt. Express 24, A650 (2016)

  37. 3-Multi-periodic/complex absorbers • Increasing the absorption bandwidth in the low absorption domain Supercell lattice: 3x3 Depth (h) cSi Metal Shift Pseudo-disordered pattern = supercell of randomly located holes, periodically repeated in a square lattice.

  38. 3-Multi-periodic/complex PhC absorbers • Increasing the absorption bandwidth in the low absorption domain • Experiments: 3x3 supercell pseudo-disordered structure (EBL+RIE) Smaller amplitude peaks Broaden peaks New peaks

  39. 3-Multi-periodic/complex PhC absorbers • Increasing the absorption bandwidth in the low absorption domain Square lattice Pseudo-disorder Relative increase Experimental 2.1% 2.7% Theoretical Shift !! Metrics !!  over 2% relative increase, in the best cases

  40. 3-Multi-periodic/complex PhC absorbers • Design rules: realspaceanalysis2µm thick c-Si H. Ding et al. Opt. Express 2016 2 x 2 3 x 3 4 x 4 holes are evenly distributed high !! Metrics !! Jsc (mA/cm²) low Clusters of holes appeared

  41. 3-Multi-periodic/complex PhC absorbers • Design rules: realspaceanalysis2µm thick c-Si H. Ding et al. Opt. Express 2016 2 x 2 3 x 3 4 x 4 • Efficient design of optimized light-trapping structures !! Metrics !!

  42. Outline L’optique pour le photovoltaïque • Introduction: nanophotonics and solarenergy conversion • Photoniccrystals and solarcells • Physics and modal engineering, case of a-Si:H • Thin c-Si solarcellsassisted by PhCs • Multi-periodic/complexabsorbers • Absorption enhancementwith pseudo-disorderednanopatterns • Design rules for solarcellsincludingcomplex patterns • PhCs for wavelength conversion • Rare earthdopedphotonicmetastructures for down shifting • Conclusion and outlook

  43. Periodic photonic structures for energy harvesting L’optique pour le photovoltaïque • High index contrast periodic structures: • a platform for Photovoltaics U. Delaware INL INL GIST Wavelength-selective intermediate mirror High efficiency absorber Resonant wavelength converter Antireflecting structure AR “layer” Absorber (Si in this talk) Solar cells Back electrode/reflector

  44. Periodic photonic structures for energy harvesting L’optique pour le photovoltaïque • High index contrast periodic structures: • a platform for Photovoltaics U. Delaware INL INL GIST Wavelength-selective intermediate mirror High efficiency absorber Resonant wavelength converter Antireflecting structure RE-doped “layer” (AR+converter) Absorber (Si in this talk) Solar cells Back electrode/reflector

  45. 4-PhC for wavelength conversion • Rare-earthdopedphotonicmeta-structure Rare earth doped layer e.g. Eu-doped Y2O3 SiNx Photonic crystal LDS Layer Visible photons (611 nm) UV photons (~ 400nm) Collab.: B. Moine, A. Pillonnet, A. Pereira

  46. 4-PhC for wavelength conversion • Rare-earthdopedphotonicmeta-structure, luminescence measurements with an integrating sphere L=250nm and r=80nm Collab.: N.-V. Hoang, B. Moine, A. Pillonnet, A. Pereira Strong Enhancement in Eu3+ emission → Expected improvement of down shifting efficiency N.-V. Hoang et al. (in preparation)

  47. 4-PhC for wavelength conversion • Photonic resonances at absorption wavelengths: Measured Transmittance RCWA Simulation Histogram from SEM images (1mm2) Bloch modes resonances • Clear evidence of the resonant modes • Transmittance remains high at longer wavelength N.-V. Hoang et al. (in preparation)

  48. 4-PhC for wavelength conversion • Photonic modes at emission wavelengths: Excitation (394 nm) q Emission (611 nm) • Clear evidence of the resonant modes • Oblique emission 611 nm N.-V. Hoang et al. (in preparation)

  49. 5-Conclusions, outlook In-plane Bloch modes and vertical “channeling” modes PhC absorbers Mediators to control incident light capture and absorption  Enables to increase Abs/JSC by 100% Photonic crystal solar cells  Dedicated processes developped: nanopatterning, passivation Positive impact of controlled perturbations  Experimental assessment of the integrated absorption increase in a- Si:H and c-Si based stacks. Strong enhancement of down shifting thanks to PhCs  x50, expected PV conversion efficiency Still many work to do in photonics:  Towards Jsc>30mA/cm² with a Si layer of less than 10µm  Develop advanced light trapping for other families of solar cells.  Other light-matter interaction effects, useful for PV (down-conversion…)

  50. Periodic photonic structures for energy harvesting L’optique pour le photovoltaïque • High index contrast periodic structures: • a platform for Photovoltaics U. Delaware INL INL GIST Wavelength-selective intermediate mirror High efficiency absorber Resonant wavelength converter Antireflecting structure AR “layer” Absorber (Si in this talk) Solar cells Back electrode/reflector

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