Plastic Electronics
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Transcript of Plastic Electronics
Plastic Organic Electronics
Presented by : Dagmawi Belaineh
Shuvan Prashant TuragaAs part of PC5212 Physics of Nanostructures Coursework
Outline
Introduction Organic LEDs Organic Photovoltaics
State of the art Conclusion
The use of π-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 ?
XNobel Chemistry 2000 goes to
For their work on conductive polymers…
Electronic structure
ethylene allyl butadiene pentadienyl hexatriene benzene
Electronic structure
Van der Waals forces 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 couplingHamiltonian
composed of components
for
Charge 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.pdf
PLED 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
circuit external in the flowing electrons # device he within tevents formation exciton #
Organic Photovoltaics
Source : Konarka C. 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
Photon Absorption ~1fs ηa
Exciton Formation
~100fs to 1ns
Exciton Diffusion ~ 1ns ηED
Exciton Breakup ~ 100 fs
Charge transport ηCT
Charge Collection ~1 us
ηCC
OPVs : Device Physics
ANOD E
CATHODE
-
+
LUMO
HOMO
Light
External Quantum Efficiency(EQE) = ηa ηED ηEB ηCT ηCC
DONOR ACCEPTOR
CharacterizationIV Characteristicsη = 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 – 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
Organic Solar Cell ArchitecturesPlanar HeterojunctionTypically exciton diffusion length = 10 nm Layer width limitedBut atleast should be 100 nm to absorb light
completely
GlassTransparent Electrode
Donor LayerAcceptor LayerMetal Electrode Bulk 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 ηe = 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 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
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 Methodology
Roll 2 Roll Manufacturing
DUV
Solvent Wash
Spin Coating/ Ink Jet Printing
DUV
Solvent 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
ITOTFB 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 eV
DOPING
Sivaramakrishnan et al, APL 2009
Efficient bipolar injection 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
Organic PV Road Ahead…
Presented at Large Area, Organic & Printed Electronics Convention, 2010
Bright Future of OLEDs
Source : http://www.oled-display.net
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
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!
Sources
1. http://parsleyspics.blogspot.com/2011/02/stop-glenn-beck-new-petition-letter.html2. http://courses.chem.psu.edu/chem210/mol-gallery/pi-systems/pisystems.html3. http://www.blazedisplay.com/LCD_Knowledge.asp?Id=484. 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 Transport6. 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