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Luminescent Solar Concentrators: Nanorods and Raytrace Modeling

Luminescent Solar Concentrators: Nanorods and Raytrace Modeling. R.Bose , D.J.Farrell , A.J.Chatten , A.Büchtemann , J.Quilitz , A.Fiore , L.Manna and K.W.J.Barnham rahul.bose@imperial.ac.uk. Overview. Introduction Making PV energy more cost-effective How the Thin Film LSC works…

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Luminescent Solar Concentrators: Nanorods and Raytrace Modeling

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  1. Luminescent Solar Concentrators: Nanorods and Raytrace Modeling R.Bose, D.J.Farrell, A.J.Chatten, A.Büchtemann, J.Quilitz, A.Fiore, L.Manna and K.W.J.Barnham rahul.bose@imperial.ac.uk

  2. Overview Introduction • Making PV energy more cost-effective • How the Thin Film LSC works… • Why Thin Films? Nanorod LSCs • Nanorod Characteristics • Spectral Measurement • Short-Circuit Current Measurement Modeling • The Raytrace Model • Fitting Nanorod Parameters • Investigating the Self-Absorption

  3. Making PV energy more cost-effective • The LSC is inexpensive compared to PV cells • Flat concentrator • Static (requires no solar tracking) • Collects direct and diffuse irradiation • Emission can be matched to the PV cells attached • Well suited for building integrated PV

  4. How the Thin Film LSC works… Light collection over large surface and emission out of small edges Thin Film Luminescent center Substrate

  5. Why Thin Films? • More convenient fabrication • Thin films allow for a flexible choice of substrates • Thin film LSCs perform just as well as homogeneously doped LSCs • Increased re-absorption losses in the optically dense film are balanced by reduced losses in the clear substrate • Supported by experimental and computational results [1] • Small separation between luminescent centers in the film can be utilized for Förster/fluorescence resonance energy transfer (FRET), which can lead to significant reduction of loss mechanisms [1] R. Bose, K.W.J. Barnham et al, 22nd EUPVSEC, Milan (2007)

  6. Nanorod LSCs Fabricated by A. Büchtemann and J. Quilitz at the Fraunhofer IAP Imperial College London

  7. Nanorod Characteristics Core-shell nanorods grown at the National Nanotechnology Laboratory of CNR-INFM [2] L. Carbone, L. Manna et al, NanoLett. 7, 2007, pp. 2942

  8. Nanorod Characteristics • Nanorod aspect ratio: 4 (5nm x 20nm) • Luminescence quantum efficiency (QE): ~ 70% • Little self-absorptions expected • Anisotropic emission expected • Maximal in plane perpendicular to long axis [2] L. Carbone, L. Manna et al, Nano Lett. 7, 2007, pp. 2942

  9. Spectral Measurement Homogeneous 40x13x4 mm3 Thin Film 1 / 2 50x50x3 mm3 +9 µm/ 15 µm

  10. Short-Circuit Current Measurement Experimental method • LSC under fairly uniform illumination from a lamp • Photodetector used to measure incident light over a grid of points • Same detector used to scan the emission from one edge • Photon count deduced using the known detector response [3] A.J.Chatten, K.W.J.Barnham et al., Semi­conductors 38, 2004, pp. 909 Photodetector Incident light LSC

  11. Incident Light Short-circuit current [µA]

  12. Incident Light Short-circuit current [µA]

  13. Spectra

  14. Results

  15. The Raytrace Model Versatile model using geometrical optics

  16. Fitting Nanorod Parameters Nanorod parameters to fit • Fundamental emission spectrum • Luminescence quantum efficiency (QE) Procedure • Modeled the LSCs and the experimental setup • Modeled photodetector using measured angular response and QE • Used short-circuit current data and measured PL spectra • Adjusted fundamental emission and QE until match with experimental data from PL and short-circuit current measurements

  17. Fitting the Fundamental Emission Example: Thin Film 2

  18. Fitting the Quantum Efficiency Homogeneous LSC • QE of 67±4% • In good agreement with value of ~70% for nanorods with this aspect ratio in solution Thin film LSCs • Worse performance (effective QEs ~40% and ~30%) • Expect homogeneous and thin film LSCs to be similar in general • Lower output could be due to agglomeration of nanorods and macroscopic defects in the film

  19. Investigating the Self-Absorption Do nanorods have less self-absorption than quantum dots? Absorption coefficients fitted to give equal absorption of incident light

  20. Investigating the Self-Absorption Modelled a 1m x 1m x 3mm LSC under AM1.5 irradiation • with Quantum Dots (commercially available green QDs) and with the nanorods (homogeneous) • Both with the same amount of absorption of incident (relative difference < 0.5% ) Results • QD LSC has ~7% more re-absorptions than the NR LSC • The effect on the edge emission is significant • NR: 1.12% of incident light (300-700nm) • QD: 0.65% of incident light (300-700nm)  Nanorods show reduced re-absorption losses.

  21. Conclusion • Nanorods were successfully incorporated in LSCs • The spectra in the LSC matrix were comparable to those in solution • A short-circuit current measurement was carried out • The LSCs were simulated with the raytrace model • The fundamental emission spectra and QEs were fitted • The QE of 67% for the homogeneous LSC was in good agreement with the quoted QE for rods with the given aspect ratio in solution • The performance of the thin film samples was worse than predicted, possibly due to defective films • Nanorods are promising as they show reduced re-absorptions

  22. Thank you.

  23. Rahul Bose rahul.bose@imperial.ac.uk +447811151835

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