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Substantially Conductive Polymers. Part 02. Usually, soliton is served as the charge carrier for a degenerated conducting polymer (e.g. PA) whereas polaron or bipolaron is used as charge carrier in a non-degenerated conducting polymer (e.g. PPy and PANI).

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slide5

Usually, soliton is served as the charge carrier for a degenerated conducting polymer (e.g. PA) whereas polaron or bipolaron is used as charge carrier in a non-degenerated conducting polymer (e.g. PPy and PANI)

Schematic structure of (a) a positive polaron, (b) a positive bipolaron,

and (c) two positive bipolarons in polythiophenes

slide11

Filtration, membranes

  • Rechargeable batteries
  • Radar absorbers
organic light emitting polymer
Organic Light Emitting Polymer
  • First reported in 1990 (Nature1990, 347, 539)
  • Based on poly(p-phenylenevinylene) (PPV), with a bandgap of 2.2 eV

ITO: Indium-tin-oxide-A transparent electrical conductor

slide14
Threshold for charge injection (turn-on voltage): 14 V (E-field = 2 x 106 V/cm
  • Quantum efficiency = 0.05 %
  • Emission color: Green
  • Processible ? No!!
  • Polymer is obtained by precursor approach. It cannot be redissolved once the polymer is synthesized
other ppv derivatives
Other PPV Derivatives
  • MEH-PPV
  • More processible, can be dissolved in common organic solvents (due to the presence of alkoxy side chains)
  • Fabrication of Flexible light-emitting diodes(Nature1992, 357, 477)
slide16

Substrate: poly(ethylene terephthlate) (PET)

Anode: polyaniline doped with acid-a flexible and transparent conducting polymer

EL Quantum efficiency: 1 %

Turn-on voltage: 2-3 V

other examples of light emitting polymers
Other Examples of Light Emitting Polymers

Poly(p-phenylene) (PPP)

BLUElight

emission

Poly(9,9-dialkyl fluorene)

CN-PPV: RED light emission

Nature1993, 365, 628

Polythiophene derivatives

A blend of these polymers produced variable colors, depending on the composition

Nature1994, 372, 443

applications
Applications
  • Flat Panel Displays: thinner than liquid crystals displays or plasma displays (the display can be less than 2 mm thick)
  • Flexible Display Devices for mobile phones, PDA, watches, etc.
  • Multicolor displays can also be made by combining materials with different emitting colors.
slide19

For an Electroluminescence process:

Electrons

Photons

Can we reverse the process?

Photons

Electrons

YES!

Photodiode

Production of electrons and holes in a semiconductor device under illumination of light, and their subsequent collection at opposite electrodes.

Light absorption creates electron-hole pairs (excitons). The electron is accepted by the materials with larger electron affinity, and the hole by the materials with lower ionization potential.

slide20

A Two-Layer Photovoltaic Devices

  • Conversion of photos into electrons
  • Solar cells (Science1995, 270, 1789; Appl. Phys. Lett. 1996, 68, 3120)
  • (Appl. Phys. Lett. 1996, 68, 3120)

490 nm

Max. quantum efficiency: ~ 9 %

Open circuit voltage Voc: 0.8 V

slide21

Another example: Science1995, 270, 1789.

ITO/MEH-PPV:C60/Ca

Active materials: MEH-PPV blended with a C60 derivative

light

ITO/MEH-PPV:C60/Ca

MEH-PPV

dark

e-

h+

light

C60

ITO/MEH-PPV/Ca

dark

slide22
A Photodiode fabricated from polymer blend

(Nature1995, 376, 498)

Device illuminated at 550 nm (0.15 mW/cm2)

Open circuit voltage (Voc): 0.6 V

Quantum yield: 0.04 %

slide23
Field Effect Transistors (FET)
    • Using poly(3-hexylthiophene) as the active layer
    • “All Plastics” integrated circuits(Appl. Phys. Lett. 1996, 69, 4108; recent review: Adv. Mater. 1998, 10, 365)
more recent development
More Recent Development
  • Use of self-assembled monolayer organic field-effect transistors
  • Possibility of using “single molecule” for electronic devices

(Nature2001, 413, 713)

slide27

Polymer light-emitting diodes, such as the one produced by Martin Drees (Ph.D. 2003) in Prof. Heflin's laboratory, may potentially yield flexible, inexpensive flat-panel displays.

Prof. Heflin's group is developing organic solar cells that have the potential to be flexible, lightweight, efficient renewable energy sources. Photograph by John McCormick.

http://www.phys.vt.edu/~rheflin/

slide28

Prof. Heflin's group is examining how nanoscale control of the composition of organic solar cells consisting of semiconducting polymers and fullerenes can improve their power conversion efficiency.

Prof. Heflin's group is using self-assembly of nanoscale organic films to create organic electrochromic devices that change color when a voltage is applied at rates up to 50 Hz.

http://www.phys.vt.edu/~rheflin/

slide29

Prof. Heflin's group is using self-assembly of nanoscale organic films to create organic

electrochromic devices that change color when a voltage is applied at rates up to 50 Hz.

http://www.phys.vt.edu/~rheflin/