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