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Nanoparticle Solar Cells Strategy to improve efficiency

Nanoparticle Solar Cells Strategy to improve efficiency. Coating, Drying. Solvent Removal. Colloid. Coating, Drying. Side. Precipitation. Solution. Chemical Reaction. Precipitation. Precursor Solution. Chemical Reaction. Drying. Side.

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Nanoparticle Solar Cells Strategy to improve efficiency

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  1. Nanoparticle Solar Cells Strategy to improve efficiency

  2. Coating, Drying Solvent Removal Colloid Coating, Drying Side Precipitation Solution Chemical Reaction Precipitation Precursor Solution

  3. Chemical Reaction Drying Side If, chemical reaction is slow, heterogeneous nucleation can occur ex) Chemical Bath Deposition

  4. PV Performance TFT device : Lateral transport Mobility is major factor → Carrier scattering is important Photovoltaic device : Vertical transport Carrier dessociation is major factor → Carrier recombination is important

  5. Surface trap-enhanced recombination • Defect trap sites on pore surface • Self-trapping due to difference of dielectric constants between solid material and air • PRB Vol. 73, 235350 (2006) • Dielectric constant of CuInSe2: ε~11.8 • Materials Letters Vol.29, 87 (1996) • Nonradiative recombination rate is proportional to the • midgap trap state density from Shockley-Read-Hall model Pore & PV efficiency

  6. Dye-sensitized solar cell Interface : TiO2 / Dye Excitons from dye Sintered PN diode solar cell Interface : Absorber / Air Excitons from Absorber Pore & PV efficiency

  7. Dye-sensitized solar cell Electron-hole pairs are generated in dye Only electrons are injected to TiO2 Electrons have almost no chance to recombine PN diode solar cell Electron-hole pairs are generated in Absorber Electron-hole pairs have chance to recombine + - Pore & PV efficiency - +

  8. Photovoltaics from quantum dots Nanoparticle Ink QD-sensitized solar cells QD solar cells QD Photovoltaics

  9. Multiple Exciton generation

  10. Intermediate band solar cell (IBSC) • If quantum dots are produced in an ordered array within an insulating medium • the wavefunctions will overlap • creating ‘mini-bands’ within the insulating region Ideal states The lowest empty mini-band energy level should be roughly one-third of the bandgap energy of the semiconductor (of the n- and p-type regions) above the valence band energy to maximize the device efficiency

  11. Exciton Bohr radius Exciton Bohr Radius of CuInS2 About 4.1 nm – 8nm JAP, vol. 65, 401 Adv. Mater. Vol. 11, 643 → Very fine particle is required Quantum Confinement

  12. Mg QD Photovoltaics MEH-PPV/PbS QD (8.5nm) PPV – Hole transport layer ITO Glass Short circuit internal quantum efficiency : 0.006%

  13. Quantized energy level in PbSnanocrystals Absorption spectrum of PbS QD QD Photovoltaics Multiple absorption peak→ Multiple excitonic transition Bandgap widening→ Multiple excitonic transition

  14. ThiolPassivation Conversion efficiency : 2.6% (Under 76 mW/cm2 at 1 μm wavelength) Achieved by ethanethiol treatment Benefits of thiol treatment Shortening of interdot distance Improved cross-linking of dots Improved surface passivation

  15. Device configuration : Schottky PV Al Ethanthiol treatment prior to Al deposition (Wetting films in dilute solution for 30s) ITO Glass Efficiency improvement by ethanethiol treatment ThiolPassivation Efficiency improvement : 0.19% → 2.6% (Under 76 mW/cm2 at 975 nm wavelength) Overtreated films formed cracks → Device shorting

  16. Improved trap passivation VOC decay measurement : Longdecay is a signature of trapped charges ThiolPassivation PLQE measurement : Increased PLQE due to suppression of nonradiative recombination at midgap trap state

  17. Depletion region deepining Interface traps decrease amount of band bending → Undesirable ThiolPassivation C-V measurement : By ethanethiol treatment, Vbi is increased

  18. Other factors Carrier drift lengths : Have little impact because they exceed device thickness Carrier diffusion length : Modestly decreased → No benefit ThiolPassivation

  19. Hexanethiol Fluorescence spectra of CuInS2 QD Strong ligandpassivate well surface defects → Nonradiative recombination is decreased → Quenching of fluorescence emission is prevented ThiolPassivation TOPO Pyridine

  20. To increase efficiency 1. Eliminate CIGS/Air interface Pores have to be filled or covered with solid material having sufficient dielectric constant 2. Passivate surface defects Proper binder material can be used for sintering process Surface treatment after sintering Future work Find adequate binder material that is : Appropriate for sintering process Useful for providing passivation Conclusion

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