Theories of charge transport in OLEDs

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Theories of charge transport in OLEDs

• Speaker ???
• Adviser Dr.???

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outline

• motivation
• Overview the current mechanism
• Charge transport
• Experiment
• Conclusion

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Motivation of development of organic electronic
devices

• low cost and various kinds of substrate
• Traditional devices restrict to silicon
  substrate, though with a better performance.
• Attractive application
• the novel flat-panel display

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Obstacles

• Research difficulties
• Complexity of interface
• Hard to identify trap distribution
• Necessity
• electrical contact with other components
• significant issue if new material
• Goal
• To overcome energy barrier.
• Trade off between trap and cost.

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Current picture about the operating mechanism

• Charge injection
• FN theory, RS theory
• Charge transport
• Space charge limited current (SCLC) theory with
  its derivatives.
• Recombine
• Electron hole -gt exciton
• Relaxation
• Exciton -gt photon or phonon/quenched.

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Carrier injection
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Early theories

• Fowler-Nordheim theory Richard-Schottky theory
• fail to consider the amorphous nature of the
  organic.
• Amorphous, not crystalline
• Organic, not semiconductor
• However,
• J 8 mobility DOS
• Monti-Carlo Simulation (1993)

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Energy diagram of RS FN
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Charge transport
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3 characteristics of OLED

• Insulator-like
• Eg large-gtn0 very small
• V large -gt ni large
• When nigtgtn0 -gt SCLC
• Disorder
• Molecule, not lattice
• Trap
• Poole-Frenkel effect
• Self trap

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Assumptions of SCLC

• Has a good contact ohmic contact
• Has band ballistic transport
• We introduce exponential-distributed trap here.
• Slope at high field is constant.JKVm

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JV
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Experiment
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experiment

• Device structure
• metal/Alq/metal
• Goal
• Work ft dependence
• temperature dependence
• Thickness dependence

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Al/Alq(1500A)/Al
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Conclusion future work

• While SCLC theory has describe charge transport
  very well, a comprehensive theory to charge
  injection is needed.
• If TCLC is applied, current approximation is not
  adequate from slope and scale view.

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reference

• M. A. Baldo and S. R. Forrest PHYSICAL REVIEW B,
  VOLUME 64, 085201
• J. Campbell ScottJ. Vac. Sci. Technol. A 21.3.
• M. A. Lampert,current injection in solids
• Thanks for your attention!