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Nanocrystal Solar Cells

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Nanocrystal Solar Cells

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    1. Nanocrystal Solar Cells Solar Photovoltaics and Energy Systems EY-1.1

    2. Outline Diameter smaller than bohr radius for the exciton => 3dim spherical quantum well Diameter smaller than bohr radius for the exciton => 3dim spherical quantum well

    3. What are Nanocrystals? Diameter smaller than bohr radius for the exciton => 3dim spherical quantum well Comercialized, liter wise batch production, low T, liquid phase… Diameter smaller than bohr radius for the exciton => 3dim spherical quantum well Comercialized, liter wise batch production, low T, liquid phase…

    4. What are Nanocrystals? Tunable bandgap Strong absorptin at shorter wavelengths Inorganic properties: scalable and controlled synthesis, ability to be processed in solution, « no » sensitivity to additional dopingTunable bandgap Strong absorptin at shorter wavelengths Inorganic properties: scalable and controlled synthesis, ability to be processed in solution, « no » sensitivity to additional doping

    5. Why use Nanocrystals? Fine tune to get Shokly-Quessier efficiency for single junctionsolar cell (31%) Go up to 66% by utilizing HOT photogenerated carriers Fine tune to get Shokly-Quessier efficiency for single junctionsolar cell (31%) Go up to 66% by utilizing HOT photogenerated carriers

    6. Why use Nanocrystals? Hot electron transport -> To increase the output voltage (rate of sepration, transport > rate of cooling) Impact ionization -> To increase output current (rate of II > rate of cooling)Hot electron transport -> To increase the output voltage (rate of sepration, transport > rate of cooling) Impact ionization -> To increase output current (rate of II > rate of cooling)

    7. How to use those Nanocrystals? P-I-N junction => creates a potential to separate charge carriersP-I-N junction => creates a potential to separate charge carriers

    8. Hybrid Nanorod-Polyemer Solar Cells Pure inorganic=>expensive // pure organic=>inefficient =>use blend Low current mobility (ineffective hopping charge transport)Pure inorganic=>expensive // pure organic=>inefficient =>use blend Low current mobility (ineffective hopping charge transport)

    9. Hybrid Nanorod-Polyemer Solar Cells A: external quantum efficency: 55% at A: external quantum efficency: 55% at

    10. Hybrid Nanorod-Polyemer Solar Cells

    11. Air-stable all-inorganic Solar Cell Hybrid cell: low hole mobility in polymer, Sensitivity to environment =>Replace organic part by inorganic CdTe D. Solvent pyridine-> spin casted to FLEXIBLE film Hybrid cell: low hole mobility in polymer, Sensitivity to environment =>Replace organic part by inorganic CdTe D. Solvent pyridine-> spin casted to FLEXIBLE film

    12. Air-stable all-inorganic Solar Cell Normalized photocurrent spectral response and absorption spectra of CdTe, CdSe solutions => See both caracteristic=> both contribute to photocurrent B. I-V characteristic dark and under simulated Air Mass 1.5 Global Other devices with varying nc diameter yields 0.6 Voc Column 3-4-5-6 Difference from p-n junctions: no free carrier w/o light illumination=> unlikly creation of depletion region CdSe (CdTe) films are insulating in dark (linear-Ohmic- IV curves) with 500Gohms/cm2 Under light, 10 times less Device: 3 orders of magnitude =>like organics: limited number of untrapped carriers in dark, best described by rigid band model Normalized photocurrent spectral response and absorption spectra of CdTe, CdSe solutions => See both caracteristic=> both contribute to photocurrent B. I-V characteristic dark and under simulated Air Mass 1.5 Global Other devices with varying nc diameter yields 0.6 Voc Column 3-4-5-6 Difference from p-n junctions: no free carrier w/o light illumination=> unlikly creation of depletion region CdSe (CdTe) films are insulating in dark (linear-Ohmic- IV curves) with 500Gohms/cm2 Under light, 10 times less Device: 3 orders of magnitude =>like organics: limited number of untrapped carriers in dark, best described by rigid band model

    13. Air-stable all-inorganic Solar Cell B. I-V characteristic dark and under simulated Air Mass 1.5 Global Other devices with varying nc diameter yields 0.6 Voc Column 3-4-5-6 Extraction by diffusion (type II heterojunction)B. I-V characteristic dark and under simulated Air Mass 1.5 Global Other devices with varying nc diameter yields 0.6 Voc Column 3-4-5-6 Extraction by diffusion (type II heterojunction)

    14. Air-stable all-inorganic Solar Cell External quantum efficiency: Percentage of electrons collected per incident photon w/o corrections C illustrates the role of charge transfer (~200 nm thick, similar OD accross spectrum) + separation of h and e at the interface increases the efficiency (less chances to recombine) + blend works => not p-n type junctionExternal quantum efficiency: Percentage of electrons collected per incident photon w/o corrections C illustrates the role of charge transfer (~200 nm thick, similar OD accross spectrum) + separation of h and e at the interface increases the efficiency (less chances to recombine) + blend works => not p-n type junction

    15. Air-stable all-inorganic Solar Cell No schottky, no pn thus D-A (organic) behavior Inorganic: work better with blend No selective contact from electrode here (e and h can be passed in both material) => current can be passed in both direction in blend cell Exciton not separated at the junction but from the little confinement along the rod length=>e&h in same donnor=>more suceptible recombination +they are traps on the surfaceNo schottky, no pn thus D-A (organic) behavior Inorganic: work better with blend No selective contact from electrode here (e and h can be passed in both material) => current can be passed in both direction in blend cell Exciton not separated at the junction but from the little confinement along the rod length=>e&h in same donnor=>more suceptible recombination +they are traps on the surface

    16. Air-stable all-inorganic Solar Cell Minimize the high surface trap area Device remains insulating in dark but 100 better in photoconductivity Red shift (to bulk like) Vos == => same driving force for charge extraction in un/sintered devices Minimize the high surface trap area Device remains insulating in dark but 100 better in photoconductivity Red shift (to bulk like) Vos == => same driving force for charge extraction in un/sintered devices

    17. Air-stable all-inorganic Solar Cell They are robustThey are robust

    18. Discussion

    19. The end?

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