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Light trapping with particle plasmons

Light trapping with particle plasmons. Kylie Catchpole 1,2 , Fiona Beck 2 and Albert Polman 1 1 Center for Nanophotonics, FOM Institute AMOLF Amsterdam, The Netherlands 2 Australian National University Canberra, Australia. Poor absorption below the bandgap. Indirect bandgap

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Light trapping with particle plasmons

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  1. Light trapping with particle plasmons Kylie Catchpole1,2, Fiona Beck2 and Albert Polman1 1Center for Nanophotonics, FOM Institute AMOLF Amsterdam, The Netherlands 2Australian National University Canberra, Australia

  2. Poor absorption below the bandgap Indirect bandgap Semiconductor (Si): poor absorption just below the bandgap  thick cell required Eg solar spectrum Si solar cell

  3. Solution: light trapping f f subs subs f air • Goal: • Increased efficiency (IR response) • and/or • Reduced thickness (=cost)

  4. Plasmon-enhanced photocurrent: 5 examples Schaadt et al., APL 86, 63106 (2005) Si SiSOI Stuart and Hall, APL 69, 2327 (1996) Derkacs et al., APL 89, 93103 (2006) SOI a-Si Nakayama et al., APL 93, 121904 (2008) Pillai et al., JAP 101, 93105 (2007) GaAs

  5. Plasmon-enhanced photocurrent: 5 examples Schaadt et al., APL 86, 63106 (2005) Si SiSOI Stuart and Hall, APL 69, 2327 (1996) Derkacs et al., APL 89, 93103 (2006) SOI a-Si What are the physical principles and limitations Nakayama et al., APL 93, 121904 (2008) Pillai et al., JAP 101, 93105 (2007) GaAs

  6. Light scattering E  p p Rayleigh scattering from point dipole Scattering from point dipole above a substrate p 4 % Preferential scattering into high-index substrate 96 % See, e.g.: J. Mertz, JOSA-B 17, 1906 (2000)

  7. Metal nanoparticle scattering (a) (b) Scattering vs Ohmic lossesAlbedo  1 for D > 100 nm Resonant scattering Ag Albedo Absorption ~ r3 Scattering ~ r6 Plasmon resonance: = -2m()

  8. Metal nanoparticle scattering All light captured and scattered into substrate (=AR coating) Cross section > 1

  9. Resonance tunable by dielectric environment Ag, D=100 nm Si(n=3.5) Si3N4 (n=2.00) Q Q O D D H Optics Express (2008), in press

  10. From point dipole to particle plasmon 0 96 % FDTD calculations Fraction scattered into substrate highest for cylinder & hemisphere:Strongest near-field coupling Tradeoff: larger size  larger albedo but lower coupling Appl. Phys. Lett. 93, 191113 (2008)

  11. Maximum path length enhancement f f subs subs 30 x Path length enhancement (A=0.90) f (A=0.95) air Fraction scattered into substrate Geometric series Highest path length enhancement for cylinder and hemisphere Appl. Phys. Lett. 93, 191113 (2008)

  12. Scattering cross-section with dielectric spacer σscat normalized to particle area Larger spacing: Interference in driving field But: lower coupling fraction (+ local density of states variation modifies albedo) Q 30 nm tot D sub 10 nm Appl. Phys. Lett. 93, 191113 (2008)

  13. Ag nanoparticle formation on SiO2/Si3N4/TiO2 on Si Thermal evaporation of 14 nm Ag + 300 °C anneal Thermal SiO2dave= 135 nmf = 26%n=1.46 LPCVD Si3N4 dave= 220 nm f = 28%n=2.00 APCVD TiO2 dave= 215 nm f = 30%n=2.50

  14. Optical absorption (1-R-T) in Si wafers Integrating sphere SiO2Si3N4 TiO2 30 nm 100 μm c-Si c-Si SiO2 Si3N4 Ref. Ref. TiO2 TiO2 Strongly enhanced near-IR absorption egineered by dielectric spacer Si3N4 AR effect, interference for shorter wavelength + redshift SiO2

  15. Photocurrent, external quantum efficiency Si3N4 front TiO2 front SiO2 front back back back Red-shifted EQE enhancement with refractive index of underlying dielectric Decrease at short wavelength due to phase shift Small increase at long wavelength for TiO2

  16. Relative photocurrent, EQE enhancement TiO2 back front Si3N4 SiO2 SiO2 Si3N4 TiO2 TiO2 coated Si: EQE enhancement 2.7 fold at λ = 1050 nm Note: particle size and distribution are not optimized

  17. Design principles for plasmon-enhanced solar cells 1) Metal nanoparticles scat > 1 2) Coverage ~ 10-20 % required 3) D>100 nm  albedo > 0.95 i.e. Ohmic losses < 5% 4) Angular distribution (=path length) increased 5) Coupling fraction f = 0.96 for point dipole 6) f reduces for larger particle size 7) scat increases with spacer thickness 8) f decreases with spacer thickness Design parameter optimization Include: inter-particle coupling

  18. For details/references visit:www.erbium.nl VACANCIES in nano-photovoltaicssee: www.amolf.nl Appl. Phys. Lett. 93, 191113 (2008)

  19. Flexible rubber on thin glass Conform to substrate bow and roughness No stamp damage due to particles Substrate Conformal Imprint Lithography PDMS Stamp Thin glass PDMS stamp (6”) on 200 µm AF-45 glass 1 m Full-wafer soft nano-imprint Marc Verschuuren, Hans van SprangSpring MRS 2007, 1002-N03-05

  20. Angular dependence of scattered light fair W dav Lambertian dav=2 Dipoledav~1.5 Increased power around critical angle for dipole compared to isotropic Lambertian less oblique path K.R Catchpole and A. Polman, APL (2008)

  21. Tadeoff between cross section and incoupling Point dipole Optics Express (2008), in press

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