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Plastic Electronics
Organic electronics such as organic LEDs (OLEDs) and organic photovoltaics (OPVs) offer advantages over traditional electronics like being lightweight, flexible, and having low-cost production. The document discusses the electronic structures of organic materials used in these applications and how they enable charge transport. It reviews the state-of-the-art in OLED and OPV technologies and processing techniques like solution processing and vapor deposition. Photocrosslinking is highlighted as a method to improve device performance. Challenges in improving material properties, device efficiencies, and reducing costs are also outlined.
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Plastic Electronics
- 1. Plastic Organic Electronics Presentedby : Dagmawi Belaineh Shuvan Prashant Turaga As part of PC5212 Physics of Nanostructures Coursework
- 2. Outline Introduction Organic LEDs Organic Photovoltaics Stateof the art Conclusion
- 3. The use ofπ-conjugated organic materials in the production of electronic devices Light weight Flexible Low-cost production http://www.youtube.com/watch?v=TDuP8PtDJbE&feature=related Motivation : Why Organic ?
- 4. X Nobel Chemistry 2000goes to For their work on conductive polymers…
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- 6. ethylene allyl butadienepentadienyl hexatriene benzene Electronic structure
- 7. Van der Waalsforces instead of covalent bonding between polymers • narrow bands with low delocalization Conjugated molecules tend to change their geometry upon charging • electron-phonon coupling Electron-phonon coupling leading to a deformation of the lattice structure of the semiconductor • Lattice • Electron • Electron-phonon coupling Hamiltonian composed of components for Charge transport Energy
- 8. Sir Richard Friend TanChin Tuan Centennial Professor Polymer Light-Emitting Diodes
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- 12. rst is thefraction of singlet excitons, q is the efficiency of radiative decay of these singlet excitons Understanding Efficiency circuitexternalin theflowingelectrons# devicehewithin teventsformationexciton#
- 13. Organic Photovoltaics Source :KonarkaC. W. Tang, Appl. Phys. Lett. 1985, 48, 183 Major Milestone : Tang reported single heterojunction device OPV in 1985 with a power efficiency of 1% High optical absorption coefficients of organic molecules thinner solar cells
- 14. Photon Absorption ~1fs ηa Exciton Formation ~100fs to1ns Exciton Diffusion ~ 1ns ηED Exciton Breakup ~ 100 fs Charge transport ηCT Charge Collection ~1 us ηCC OPVs : Device Physics A N O D E C A T H O D E - + LUMO HOMO Light External Quantum Efficiency(EQE) = ηa ηED ηEB ηCT ηCC DONOR ACCEPTOR
- 15. Characterization IV Characteristics η =maximum deliverable electrical power(VM ×JM) to the incident light power(Pinc) FF = Fill Factor VOC = Open Circuit Voltage JSC= Short Circuit Current
- 16. Materials, • Printing – ScreenPrinting – Stamping • Spraying • Spin Coating • Vaporization Acceptors PCPDTBT, MEH-PPV, P3HT, PTB1 Donors PCDTBT, PCBM, PSBTBT Electrode Al, Ca, Ag Transparent Electrode PEDOT:PSS, ITO Krebs F. C., Solar Energy Materials & Solar Cells 93 (2009) 394–412 Processes
- 17. Organic Solar CellArchitectures Planar Heterojunction Typically exciton diffusion length = 10 nm Layer width limited But atleast should be 100 nm to absorb light completely Glass Transparent Electrode Donor Layer Acceptor Layer Metal Electrode Bulk Heterojunction Ordered Heterojunction
- 18. Now, actual SolarCells can be complex… Stacking improves efficiency Adding more layers for hole injection and electron injection adds to the cells efficiency
- 19. Tandem Cell isbetter Tandem Cell Jsc = 7.8 mA/cm2, Voc = 1.24 V, FF = 0.67, and ηe = 6.5% www.sciencemag.org SCIENCE VOL 317 13 JULY 2007 pp. 223-225
- 20. Progress in SolarCell Research 5.4% NREL Database
- 21. State of theart : • Spin coating – Can coat large areas with high speed – Redissolution – Patterning not possible as • Vapour Evaporation – Layer by layer without chemical interaction in vacuum – Non uniform, requires UHV, expensive, contamination, LOS • Vapour Deposition – Better control through gas flow rate and temperature – Uniformity and not contaminated
- 22. State of theart : Photocrosslinking Photolysis of FPA gives singlet nitrene which inserts into C-H bonds of polymers to form crosslinks Effective crosslinker conc is low !!
- 23. FPA Methodology Roll 2Roll Manufacturing DUV Solvent Wash Spin Coating/ Ink Jet Printing DUV Solvent Wash
- 24. Key Advantage :Continuity for e and h conduction paths is guaranteed. Contiguous Interpenetrating Structure for PVs
- 25. Using Photocrosslinking forPVs A factor of 4.5 improvement is achieved internal recombination bottleneck overcome
- 26. Photocrosslinking possiblewithout significant loss of device properties 4.5% external photons per injected electron Similar life time Similar results for other types of PPV Can we make heterostructures? PLEDs using PHOTOCROSSLINKING
- 27. ITO TFB the hole-transportingand electron-blocking interlayer F8BT the electron-transport and light-emitting layer Can we make heterostructures?
- 28. For solution-processedpolymer OSCs, however, this is a considerable challenge because of redissolution, and the difficulty of fixing a p-i-n profile -> photocrosslinking!!! For molecular organic semiconductors (OSCs), doping is readily achieved by coevaporation of the dopant with the transport layer (eg. by CVD) Observation of p-doping with sodium naphthalenide (Na+Np−) from transmission spectra: the band at 2.7 eV bleaches while a sub-gap polaron transition emerges at 1.8 eV Observation of n-doping with nitronium hexafluoroantimonate (NO2 +SbF6 −)from transmission spectra: the band bleaches while a different subgap polaron transition emerges at 2.1 eV DOPING Sivaramakrishnan et al, APL 2009
- 29. Efficient bipolarinjection Greatly improved external electroluminescence efficiency compared to control devices without the p-i- n structure photocrosslinking of the first layer bulk p-doping by diffusion of solution-state dopant, deposition of an intrinsic polymer layer solid-state surface n-doping to limit the doping depth in this layer Methodology
- 30. Organic PV RoadAhead… Presented at Large Area, Organic & Printed Electronics Convention, 2010
- 31. Bright Future ofOLEDs Source : http://www.oled-display.net
- 32. Challenges Material Level • OPV:Low bandgap polymers with absorption edge at 1eV, large absorption coefficients, higher charge mobilities • OLED: Low work function cathodes with higher stability • Minimise Energy Loss at junctions Process Level • To be able to create nanostructures with appropriate domain size and dimensions Device Level • Increase power conversion efficiency • Increase stability • Reduce costs • Develop a technology for large scale production and reproducibility • Ruggedness FlexibilityTransparent
- 33. Summary • Organic Electronicshas tremendous potential of replacing the present rigid electronics. • However, there are issues of cost-efficiency tradeoff which need to be dealt with. • Competitive research among the companies is empowering the progress of organics. • Dynamic and highly interdisciplinary field: physicists, chemist, material scientists, electrical engineers … truly Nano!
- 34. Sources 1. http://parsleyspics.blogspot.com/2011/02/stop-glenn-beck-new-petition-letter.html 2. http://courses.chem.psu.edu/chem210/mol-gallery/pi-systems/pisystems.html 3.http://www.blazedisplay.com/LCD_Knowledge.asp?Id=48 4. J.H. van Lienden, Charge transport in trans-polyacetylene, Thesis, Rijksuniversiteit Groningen (2006) 5. K. Walzer, B. Maennig, M. Pfeiffer, and K. Leo, Highly Efficient Organic Devices Based on Electrically Doped Transport 6. Layers, Chem. Rev. 107, 1233-1271 (2007) 7. M. Pfeiffer, S.R. Forrest, K. Leo, M.E. Thompson, Electrophloroscent p-i-n OLEDS for very high efficiency flat-panel displays, Adv. Mat. , 14, 22, (2002) 8. www.wikipedia.org