Plastic Electronics
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Plastic Electronics
Plastic Organic Electronics Presented by : Dagmawi Belaineh Shuvan Prashant TuragaAs part of PC5212 Physics of Nanostructures Coursework
Outline
The use of -conjugated organic materials in the production of electronic devices
Light weight
Flexible
Low-cost production
http://www.youtube.com/watch?v=TDuP8PtDJbE&feature=relatedMotivation : Why Organic ?
X
Nobel Chemistry 2000 goes to For their work on conductive polymers
Electronic structure
ethylene allyl butadiene pentadienylhexatriene benzeneElectronic structure
Band Gap in organics
Electron-phonon coupling leading to a deformation of the lattice structure of the semiconductorCharge transport
Energy
Sir Richard FriendTan Chin Tuan Centennial Professor
Polymer Light-Emitting Diodes
http://www.lti.unikarlsruhe.de/rd_download/polymer2004/Plastic_Electronic_WS0405_7.pdfPLED BASICS
Heterostructures
Light emission process
rst is the fraction of singlet excitons, q is the efficiency of radiative decay of these singlet excitons
Understanding Efficiency
Organic Photovoltaics
Source : Konarka
C. W. Tang, Appl. Phys. Lett. 1985, 48, 183Major 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
OPVs : Device PhysicsANOD ECATHODE
-+LUMOHOMO
LightExternal Quantum Efficiency(EQE) = a ED EB CT CC
DONOR ACCEPTOR
Characterization
IV Characteristics = maximum deliverable electrical power(VM JM) to the incident light power(Pinc)FF = Fill FactorVOC = Open Circuit Voltage JSC= Short Circuit Current
Materials, Printing Screen Printing StampingSprayingSpin CoatingVaporization
Krebs F. C., Solar Energy Materials & Solar Cells 93 (2009) 394412Processes
Organic Solar Cell ArchitecturesPlanar HeterojunctionTypically exciton diffusion length = 10 nm Layer width limitedBut atleast should be 100 nm to absorb light completely
GlassTransparent ElectrodeDonor LayerAcceptor LayerMetal ElectrodeBulk Heterojunction
Ordered Heterojunction
Now, actual Solar Cells can be complex
Stacking improves efficiency Adding more layers for hole injection and electron injection adds to the cells efficiency
Tandem Cell is better
Tandem CellJsc = 7.8 mA/cm2, Voc = 1.24 V, FF = 0.67, and e = 6.5%www.sciencemag.org SCIENCE VOL 317 13 JULY 2007 pp. 223-225
Progress in Solar Cell Research
5.4%NREL Database
State of the art : Spin coatingCan coat large areas with high speed RedissolutionPatterning not possible asVapour Evaporation Layer by layer without chemical interaction in vacuumNon uniform, requires UHV, expensive, contamination, LOSVapour DepositionBetter control through gas flow rate and temperatureUniformity and not contaminated
State of the art : Photocrosslinking
Photolysis of FPA gives singlet nitrene which inserts into C-H bonds of polymers to form crosslinksEffective crosslinker conc is low !!
FPA MethodologyRoll 2 Roll Manufacturing
DUVSolvent WashSpin Coating/ Ink Jet Printing
DUVSolvent Wash
Key Advantage : Continuity for e and h conduction paths is guaranteed.Contiguous Interpenetrating Structure for PVs
Using Photocrosslinking for PVs
A factor of 4.5 improvement is achieved internal recombination bottleneck overcome
Photocrosslinking possible without 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
ITO
TFB the hole-transporting and electron-blocking interlayer
F8BT the electron-transport and light-emitting layer
Can we make heterostructures?
For solution-processed polymer 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 eVDOPINGSivaramakrishnan et al, APL 2009
Efficient bipolar injection Greatly improved external electroluminescence efficiency compared to control devices without the p-i-n structureMethodology
Organic PV Road Ahead
Presented at Large Area, Organic & Printed Electronics Convention, 2010
Bright Future of OLEDs
Source : http://www.oled-display.net
Challenges
Summary Organic Electronics has 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!
Sourceshttp://parsleyspics.blogspot.com/2011/02/stop-glenn-beck-new-petition-letter.htmlhttp://courses.chem.psu.edu/chem210/mol-gallery/pi-systems/pisystems.htmlhttp://www.blazedisplay.com/LCD_Knowledge.asp?Id=48J.H. van Lienden, Charge transport in trans-polyacetylene, Thesis, Rijksuniversiteit Groningen (2006)K. Walzer, B. Maennig, M. Pfeiffer, and K. Leo, Highly Efficient Organic Devices Based on Electrically Doped TransportLayers, Chem. Rev. 107, 1233-1271 (2007)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)www.wikipedia.org