Substantially Conductive Polymers

1. Substantially Conductive Polymers Behzad Pourabbas Dep. Of Polymer eng. Sahand University of Technology Tabriz-Iran pourabas@sut.ac.ir

2. In order to download the PPT files: • 1- Go to SUT web page (www.sut.ac.ir/en) • 2- find the Polymer eng. Faculty (http://polymer.sut.ac.ir/) • 3- Go to my page: (http://polymer.sut.ac.ir/showcvmain.aspx?id=5) • 4- Education  Courses Ph.D Materials for IT (http://polymer.sut.ac.ir/CourseBrf.aspx?id=32) • 5- Download the files: (http://polymer.sut.ac.ir/download.aspx?id=32) • Using the file contents are allowed by referencing.

3. Overview Discovery and history The story of Polyacetylene Structural Characteristics Doping Concept The Charge Carriers Applications

4. The discoverers, the Noble laureates (Chem 2000)

6. Materials, According To Electrical Properties • insulator, • <10-7S/cm • semiconductor, • 10-4 - 10 S/cm depending upon doping degree • conductor and • >103S/cm • superconductor

7. Polymers and Conductivity • Since discovery of conductive polyacelene (PA) doped with iodine, a new field of conducting polymers, which is also called as “synthetic metals”, has been established and earned the Nobel Prize in Chemistry in 2000. • In 1977, this accidentallydiscovered that insulating π-conjugated PA could become conductor with a conductivity of 103 S/cm by iodinedoping.

8. The story of PA

9. The Story of Polyacetylene • PA could be regarded as an excellent candidate of polymers to be imitating a metal. • Because it has alternating double and single bonds, as called conjugated double bonds.

10. The Story of Polyacetylene • At the beginning of the 1970s, HedekiShirakawa at Tokyo Institute of Technology, Japan, was studying the polymerization of acetylene into plastics by using catalyst created by Ziegler-Natta. • A visiting scientist in Shirakawa’s group tried to synthesize PA in the usualway. However, a beautifully lustrous silver colored film, rather than the black powder synthesized by the conventional method, was obtained.

11. The Story of Polyacetylene • Shirakawa finally found that the catalyst concentration used was enhanced by 103 times! Shirakawa was stimulated by the accidental discovery and further found the molecular structure of the resulting PA was affected by reaction temerature, for instance, the silvery film was trans-polyacetylenewhereas copper-colored film was almost pure cis-polyacetylene.

12. The Story of Polyacetylene • In another part of the world, chemisteAlan G. MacDiarmid and physicist Alan J. Heeger at University of Pennsylvania, Philadephia, USA were studying the first metal-like inorganic polymer sulfur nitride ((SN)x ), which is the first example of a covalent polymer without metal atoms. In 1975, Prof. MacDiarmid visited Tokyo Institute of Technology and gave a talk on (SN)x. After his lecture, MacDiarmid met Shirakawa at a coffee break and showed a sample of the golden (SN)x to Shirakawa. Consequently, Shirakawa also showed MacDiarmid a sample of the silvery (CH)x.

13. The Story of Polyacetylene • The beautiful silvery film caught the eyes of MacDiarmid and he immediatelyinvitedShirakawa to the University of Pennsylvania PA. • Since MacDiarmid and Heeger had found previously that the conductivity of (SN)x could be increased by 10 times after adding bromine to the golden (SN)x material, which is called as “doping” item in inorganic semiconductor. • Therefore, they decided to add some bromine to the silvery (CH)x films to see what happens. • Miracle took place on November 23, 1976! • At that day, Shirakawa worked with Dr. C.K. Chiang, a postdoctoral fellow under Professor Heeger, for measuring the electrical conductivity of PA by a four-probemethod.

14. The Story of Polyacetylene • Surprise to them, the conductivity of PA was ten million times higher than before adding bromine. This day was marked as the first time observed the “doping” effect in conducting polymers. • In the summer of 1977, Heeger, MacDiarmid, and Shirakawaco-published their discovery in the article entitled “Synthesis of electrically conducting organic polymers: Halogen derivatives of polyacetylene (CH)n” in The Journal of Chemical Society, Chemical Communications.

15. Structural Characteristics and Doping Concept

16. Structural Characteristics and Doping Concept !

19. The concept of Doping

21. Discovery of the First Conducting Polymer

27. The Charge Carriers

32. 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

33. Typical Charge Carriers (via doping)

34. Chemical term, charge and spin of soliton, polaron and bipolaron in conducting polymers

38. Filtration, membranes • Rechargeable batteries • Radar absorbers

39. Applications

40. Potential applications and corresponding physical properties of conducting Polymers.

42. 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

43. 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

44. 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)

45. 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

46. 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

47. 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.

48. 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.

49. 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

50. 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