1 / 21

Third Generation Solar cells

Third Generation Solar cells. Hiwa Modarresi 17 th June 2009. 1. "Energy & Nano" - Top Master Symposium in Nanoscience 2009. Outline. Sunlight spectrum How a classical solar cell works First generation solar cells Second generation solar cells The main losses in solar cells

livana
Download Presentation

Third Generation Solar cells

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Third Generation Solar cells Hiwa Modarresi 17th June 2009 1 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  2. Outline • Sunlight spectrum • How a classical solar cell works • First generation solar cells • Second generation solar cells • The main losses in solar cells • Third generation solar cells • Band gap engineering • Multiple exciton generation • Hot carrier solar cells • Up conversion • Down conversion • Tandem cells • Summary "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  3. Sunlight Spectrum • Sunlight consists of a broad range of spectrum • The photon energy depends on the photon wavelength: Ephot = hc/λ • Harnessing the great amount of sunlight energy Solar Radiation Spectrum Online: http://www.globalwarmingart.com/wiki/Image:Solar_Spectrum_png 3 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  4. How a Classical Solar Cell Works Photovoltaic cell is a device that converts solar energy into electricity by the photovoltaic effect Energy of the incident photon should be greater than or equal to the band gap of the semiconductor If an exciton is created in space charge region, its electron-hole components would be separated Electric Field 4 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  5. First Generation Solar Cells Single crystal silicon wafers Dominant in the commercial production of solar cells Consist of a large-area, single layer p-n junction Best crystalline Si solar cell efficiency: ~ 25% Advantages Broad spectral absorption range High carrier mobility Disadvantages Most of photon energy is wasted as heat Require expensive manufacturing technologies 5 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  6. Second Generation Solar Cells Thin-film Technologies Amorphous silicon Polycrystalline silicon Cadmium Telluride (CdTe) Best large area Si-based solar cell efficiency: ~ 22% Advantages Low material cost Reduced mass Disadvantages Toxic material (Cd), Scarce material (Te) 6 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  7. The Main Losses in Solar Cells • Sub bandgap and Lattice thermalisation losses acount for more than 50% of the total loss Energy Lattice thermalisation loss Junction loss Contact loss Sub bandgap loss qV Recombination loss "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  8. Third Generation Solar Cells Solar cells which use concepts that allow for a more efficient utilization of the sunlight than FG and SG solar cells The biggest challenge is reducing the cost/watt of delivered solar electricity Third generation solar cells pursue More efficiency More abundant materials Non-toxic material Durability Efficiency and cost projections Third Generation FirstGeneration Second Generation ARC Photovoltaics center of Excellence, University of New Soth Wales, Annual Report (2007) 8 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  9. Band gap engineering using quantum confinment effect Multiple Exciton Generation Hot Carrier Solar Cell UpConversion Down Conversion Tandem Cells Third Generation Solar Cells 9 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  10. Band Gap Engineering Quantum confinement Discrete energy levels Excitonc Bohr radius the size of the band gap is controlled simply by adjusting the size of the dot. Thin film Si band gap: Eg = 1.12 eV 2 nm QD Si band gap: Eg = 1.7 eV Enhanced impact ionization (inverse Auger recombination) Greatly enhanced non-linear optical properties Egap 10 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  11. Multiple Exciton Generation Objective: fighting termalization In quantum dots, the rate of energy dissipation is significantly reduced One photon creates more than one exciton via impact ionization Higher photocurrent via impact ionization (inverse Auger process) Multiple exciton generation evidence PbSe (lead selenide) QDs Egap Egap 11 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  12. Hot Carrier Solar Cell Objective: fighting thermalization Energy selective contacts Need to slow carrier cooling Higher photovoltage via hot electron transport The idea is to suppress the Klemens transitions ELO>2ELA such that LO→2LA (Klemens mechanism) is forbidden The LO→TO+LA (Ridley mechanism) can occur Hot carrier evidence InN G.J. Conibeer, D. König et al., “Slowing of carrier cooling in hot carrier solar cells,” Thin Solid Films, 516, 6948-6953, (2008) 12 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  13. Up Conversion Objective: transforming large wavelength photons into small wavelengh photons Nearly half of the intensity of sunlight is within the invisible infrared region Can be implemented by quantum wells and quantum dots The drawback is that it is a non-linear effect Up conversion evidence: (Erbium) It is far from realization ½ Eg Eg ½ Eg 13 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  14. Down Conversion Objective: transforming small wavelength photons into large wavelength photons Suitable materials must efficiently absorb high energy photons and reemit more than one photon with sufficient energies can be implemented by quantum wells and quantum dots Down conversion evidence: Multiple exciton generation Egap Egap Eg 2 Eg Eg 14 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  15. Tandem Cells The only proven 3rd generation technique so far Light Upper cell (absorbs high energy photons) Middle cell (absorbs medium energy photons) Lower cell (absorbs low energy photons) 15 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  16. Tandem Cells • Nanocrystal sizes approaching the excitonic Bohr radius • Small nanocrystals of Si embedded in a silicon dielectric matrix • Annealing at 1100 oC • Multi-layers containing n-type Si QDs on p-type Si wafers G. Conibeer, M. Green et al., “Silicon quantum dot nanostructures for tandem photovoltaic cells,” Thin Solid Films, 516, 6748-6756, (2008) G. Conibeer, M. Green et al., “Silicon quantum dot nanostructures for tandem photovoltaic cells,” Thin Solid Films, 516, 6748-6756, (2008) 16 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  17. Tandem Cells • Best device in this respect, was the one with 3 nm QDs with an efficiency of 10.6% • This is comparable to a conventional p-n junction crystalline silicon solar cells with a non-textured surface ARC Photovoltaics center of Excellence, University of New Soth Wales, Annual Report (2007) "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  18. Tandem Cells • What we can also investigate: • Effect of excitonic Bohr radius • Si = 4.9 nm • Ge = 24.3 nm • Sn = 40 nm • The quantum size effects should be more prominent in Tin nanocrystals even for larger sizes of nanocrystals 18 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  19. Summary Objectives in third generation solar cells More efficient Less expensive Readily available Non-toxic Quantum confinment Band gap engineering Multiple exciton generation Already seen in QDs but with very low efficiencies Hot carriers Far from utilization Up conversion So far has not been realized Down conversion Can be utilized through the concept of multiple exciton generation Tandem cells The only proven technique in 3rd generation solar cells 19 "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  20. Acknowledgment • I want to sincerely thank my supervisor, professor G. Palasantzas whose kind attentions led me through the difficulties. "Energy & Nano" - Top Master Symposium in Nanoscience 2009

  21. THANK YOU FOR YOUR ATTENTION

More Related