Developments in organic solar cells


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Background information on organic solar cells with limitations and ways to improve efficiency

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  • Not that Si is expensive in itself, but the processing techniques to make them pure (pure crystals and organized crystals) cost a lot, because it requires high temperature process. Find out more!! Efficiency is good (mono-25% lab, 22% SolarPower), compared to 10% in lab for OSCs. (Diffusion vs Drift)
  • Many of these applications are specically targeted to the
    consumer market rather than to utility-scale generation of
  • Electric field to separate excitons: Organic materials: conjugated systems-conducting polymers,
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  • Developments in organic solar cells

    1. 1. Developments in Akinola Oyedele MSE 556 – Materials for Energy Organic Solar Cells
    2. 2. Outline • • • • • Background Evolution Limitations Future Considerations Conclusion Konarka Technologies Inc Cambridge University
    3. 3. Background
    4. 4. Conducting Polymers • In 1977, discovery of electrical conductivity in doped polyacetylene • Nobel prize in chemistry in 2000 to Alan Heeger, Alan McDiarmid and Hideki Shirakawa • 1986, Organic photovoltaic cell OPV (Ching W Tang, Kodak) • 1986, Orgaic field-effect transistor OFET (H Koezuka, Mitsubishi) • 1987, Organic light-emitting diode OLED (Ching W Tang, Kodak) Photo credit:
    5. 5. Chemical structures of conducting polymers Daniel J.Burke Energy Environ. Sci., 2013, 6, 2053
    6. 6. Advantages • • • • • • • Cheap, low-temperature deposition techniques (e.g roll-to-roll, printing) Environmental-friendly materials; Abundant and Cheap Can be semitransparent or aesthetically pleasing Ultra-flexible and even stretchable, Lightweight Low-light condition Color-tunable
    7. 7. Companies Involved 2001 (bankrupted 2012) USA, Austria 2010, Cambridge, UK 2006, Dresden, Germany 2006, El Monte, California
    8. 8. Evolution of the active layer Single-layer OSC Efficiency = 0.1 % Bi-layer OSC Efficiency = 1 % Bulk heterojunction OSC Efficiency = 10 %
    9. 9. Construction of the OPV Devices • Transparent electrode 1. As a transparent widow layer 2. Collect holes (anode) • Hole Transporting Layer 1. Protect the active layer 2. As an electron-blocking layer 3. Assist hole transport 4. Smoothen the rough surfaces of the TCO D. Ginley, Fundamentals of materials for Energy • LiF as a cathode buffer layer and Environmental Sustainability, page 232 1. To prevent diffusion of cathode elements to the active layer 2. To act as an electron-transport, Hole-blocking layer. The main challenge is they require high deposition temperature which can potentially damage the active layer
    10. 10. Energy-level band diagram Energy-level band diagram of a typical P3HT:PCBM Organic Solar Cell D. Ginley, Fundamentals of materials for Energy and Environmental Sustainability, page 233
    11. 11. Progress in Organic Solar Cells M. Gratzel, Nature 2012
    12. 12. Solar cells characteristics Diode model of a solar cell Current-voltage response of a solar cell Omar A. AbdulRazzaq, Organic Solar Cells: A review of Materials, Limitations and Possibilities for Improvements, 2013; Pg 428
    13. 13. HOMO and LUMO energy levels Energy levels in inorganic and organic semiconductors Illustration of HOMO and LUMO energy levels Tom J. Savenije, Organic Solar Cells Delft University
    14. 14. Limitations of Photocurrent in OSC • Carrier transport mechanism in OSC 1. 2. 3. 4. 5. Light absorption; Diffusion of exciton to interface; Charge separation; Charge Transport Charge Collection Omar A. AbdulRazzaq, Organic Solar Cells: A review of Materials, Limitations and Possibilities for Improvements, 2013; Pg 431
    15. 15. Limitations of Photocurrent in OSC (2) • Exciton • Charge Diffusion Separation Bulk-heterojunction solar cell Low dielectric constant Formation of exciton (tightly-bound) Frenkel excitons
    16. 16. Considerations • Collect a high number of photo-generated carriers • Use small band-gap polymers • Increase electrical conductivity by improving the crystal structure Improve crystallinity by thermal annealing of the solution-based mixture • Large donor-acceptor interface to promote the dissociation of more excitons • Brabec and Durrant, Cambridge University (2008)
    17. 17. Absorb more light • Tandem organic solar cells Behaves like cells in series Minimize thermalization losses Same-current limitation Coupling processing techniques M. Gratzel, Materials interface engineering for solution-processed photovoltaics, Nature 306, vol 488, 2012
    18. 18. Ternary Organic Solar Cells Sensitizers can be dyes, polymers or nano-particles Eliminates the challenges of multi-junction solar cells Improve the photon harvesting in thickness limited photoactive layers Limitation: Lower Voc Tayebeh Ameri Adv Mater. 2013, 25, 4243-4266
    19. 19. Cascade Charge Transfer Schematic representation of the cascade charge transfer in ternary solar cell Illustration of an optimal microstructure of the ternary blends Tayebeh Ameri Adv Mater. 2013, 25, 4243-4266
    20. 20. Parallel-like Charge Transfer Schematic representation of the parallel-like charge transfer in a ternary solar cell Tayebeh Ameri Adv Mater. 2013, 25, 4243-4266
    21. 21. Plasmonics in Organic Solar Cells • Enhance light-trapping (increase in optical path length) • First developed by Goetzberger et al. 1981 • Enable the use of ultra-thin layers (semi-transparency) Creates a strong E-field Grated back-contact Light-trapping techniques used in thin-film solar cells Atwater, H.A., and Polman, A. (2010). Plasmonics for improved photovoltaic devices, Nature Materials 9; 205-213
    22. 22. Plasmonics in OSC • The shape and size of the nano-particles greatly affect the angular spread Sensitivity of plasmon light scattering to nanoparticles’ shape and size Atwater, H.A., and Polman, A. (2010). Plasmonics for improved photovoltaic devices, Nature Materials 9; 205-213
    23. 23. Inverted OSC Efficient Inverted Polymer Solar Cells. Applied Physics Letter 88 (2006)
    24. 24. Inverted OSC (2) Hongbin Wu South China University of Technology, Guangzhou, 2012 PCE= 9.2 % current density of 17.2 mA/cm2, 15.4 mA/cm2 for the regular device.
    25. 25. Tayebeh Ameri Adv Mater. 2013, 25, 4243-4266
    26. 26. Conclusion • • • • • • • The expected high-efficiency per unit cost ratio The simplicity in fabrication and processing The mechanical flexibility of these materials The short diffusion length Low absorption of the active layer Tandem architectures incorporated with plasmons Organic cells made up of polymer nanocomposites
    27. 27. Let’s drive tomorrow today! Thank you for your attention.
    28. 28. References • • • • • • D. Burke, et al (2013). Green chemistry for organic solar cells. Energy Environ. Sci, 6: 2053 M. Graetzel, et al (2012). Materials interface engineering for solutionprocessed photovoltaics. Nature Review article 488: 304-312. O. Abdulrazzaq, et al (2013). Organic Solar Cells: A review of materials, limitations, possibilities for improvement. Particulate Sci and Tech, 31: 427-442 T. Ameri, et al (2013). Organic Ternary Solar Cells: A review. Advanced Materials, 25: 4245-4266 M. Liu, et al (2013). Efficient planar heterojunction perovskite solar cells by vapour deposition. Nature 501: 395-402 M. Green (2005). Silicon Photovoltaic Modules: A brief History of the first 50 years. Prog. Photovolt: Res. Appl. 13: 447-455