Renaissance of the Plastic Age

Polymers for Electronics & Photonics

T.P.RadhakrishnanSchool of Chemistry, University of Hyderabad

Hyderabad 500 046, Indiatprsc@uohyd.ernet.in

http://chemistry.uohyd.ernet.in/~tpr/

This file is available at http://chemistry.uohyd.ernet.in/~ch521/

Materials and civilisation

(Before 5000 BC)Stone age

(5000 - 3000 BC) Copper age

(3000 - 800 BC)Bronze age

(800 BC - 40 AD)Iron age

Plastic age ?

Metals / Alloys

Ceramics

Polymers

Types of materials

Semiconductors Composites Biomaterials

Molecular materials*Courtsey: W. D. Callister, Fundamentals of Materials Science and Engineering

*

Design of Molecular Materials

Elements / Compounds Materials

Elements / Compounds

Chemical /Physical routes

Molecules

Crystals Thin films / LB films

PolymersNanostructures

Chemical routes

Chemical / Physical routes

Natural polymers

Phenol-formaldehyde(Bakelite)

Synthetic polymers

Polyethylene Polytetrafluoroethylene(Teflon)

Polyhexamethylene adipamide(Nylon 6,6)

PolycarbonatePolyethyleneterephthalate(PET)

Discovery of conducting polymers

1862 Lethby (College of London Hospital) Oxidation of aniline in sulfuric acid

1970’s Shirakawa (Japan)

Ti(OBu)4 & Et3Al Toluene–78oC

copper-coloured film cis-polyacetylene

CH CHAcetylene gas

Ti(OBu)4 & Et3Al Hexadecane150oC

silvery filmtrans-polyacetylene

Polyacetylene (PA)

n

n

Electrical conductivity ()

cis PA 10-10 – 10-9 S cm-1 trans PA 10-5 – 10-4 S cm-1

For comparison : (copper) ~ 106 S cm-1

: (teflon) ~ 10-15 S cm-1

Doping leads to enhanced conductivity

n

n

n

+-

+ e- - e-

~ 10-5 S cm-1

Semiconductor

~ 104 S cm-1

Metal

Discoverers - Nobel Prize 2000

A. Heeger, A. McDiarmid, H. Shirakawa(this photograph taken at the International Conference on

Synthetic Metals, 2000, was kindly provided by Prof. Heeger)

Polyacetylene - electronic structure

(a) (b) (c) (d) (e)

(a) ethylene(b) allyl radical(c) butadiene

-electronic energy levels and electron occupation

(d) regular trans-PA

(e) dimerised trans-PA

How does a conducting polymer work ?

[CH]n + (3x/2) I2 [CH]nx+ + xI3

-

+

+

+

.

.

.I3

-

I3-

I3-

Oxidative doping of polyacetylene by iodine

Polaronand its delocalisation

+ . +

+

.

+oxidation

oxidation

isomerisation

Bipolaron

Neutral Soliton

Positive Soliton

Excitations

Examples of conducting polymers

S n Polythiophene

(PT)

n Polyparaphenylene

(PPP)

n

Polyparaphenylenevinylene (PPV)

n

O

O

N n Polypyrrole

(PPy)

O O

S n

Polyethylenedioxythiophene

(PEDOT)

Alkoxy-substitutedpolyparaphenylene

vinylene(MEH-PPV)

N

H

N N N

H

n Polyaniline

(PANI)

Electrical conductivities10+6

10+4

10+2

100

10-2

10-4

10-6

10-8

10-10

10-12

10-14

10-16

10-18 S cm-1

CopperPlatinumBismuthGraphite

Germanium

Silicon

Polyethylene

Diamond

Quartz

ConductingPolymers

Synthesis of PANI

Aniline +dil. HCl

Cathode

Anode(ITO plate)

Instead of electrochemical oxidation, chemical oxidation may be carried out : Aniline + acid + oxidising agent ((NH4)2S2O8)

Voltage (~ 0.3 - 0.5 V) applied

Result of electropolymerisation

The green coating on the ITO electrode is due to the formation of emeraldine salt form of PANI

Polyaniline (PANI)

HN

HN

HN

HN

HN

HN N N

N N N N

HN

HN

H+N N

X-Emeraldine salt Green

(Conductor)

Emeraldine base Blue(Insulator)

Leucoemeraldine Colorless(Insulator)

Oxidation

Purple(Insulator)

Pernigraniline

Applications of conducting polymers

Polyaniline (PANI)Transparent conducting electrodes Electromagnetic shieldCorrosion inhibitor‘Smart windows’ (electrochromism)

Polypyrrole (Ppy) Radar-invisible screen coating (microwave absorption)Sensor (active layer)

Polythiophene (PT)Field-effect transistorAnti-static coating Hole injecting electrode in OLED

Polyphenylenevinylene (PPV)Active layer in OLED

Polypyrrole - conductivity switching

Enzyme Biosensor Using PPyGlucose oxidase

-D-glucose + ½O2 + H2O D-gluconic acid + H2O2

H2O2 + 2HCl + Ppy 2H2O + Ppy2+.2Cl-

PANI-PSS

**

SO3

n

-

PSSn-

PSSn-(100 kDa)RT = 8.3x10-2 Scm-1

PSSn-(70 kDa)RT = 3.6x10-2 Scm-1

SensorsTypical example : Ammonia sensing by PANI-PSSM film

Resistance change with time

Ammonia in

Ammonia out 0 1000 2000 3000 40001.00

1.05

1.10

1.15

1.20

1.25

1.30

1.35

R/R

o

Time(sec)

0 50 100 150 200 250

1.2

1.4

1.6

1.8

2.0(R

/Ro) 15

0

Concentration of ammonia (ppm)

Resistance change at 150 sec. for different concentrations of ammonia

Electroluminescence

-

+

Metal electrode

Organic thin film

Transparentelectrode (ITO)

Light

Electric field

Principle of EL

e-

h+

Cathode Anode

HOMO

LUMO

HOMO

LUMO

Light

Polymers for Organic Light Emitting Diodes (OLED)

n

n

O

O

PPV MEH-PPV

Commercial materials like Mn2+ in ZnS require 100V DCPPV : requires 5 - 10V DC

runs even with ACbrightness ~40,000 cd/m2 ie. ~100 times brighter than a TV screen

Ca/Ag

MEH/PPV

SilicaGold

P3HT

n+-Silicon

Aluminium

Silica

G

D S

Organic LED driven by organic transistor

Electrochromic devices

Viewing side

Li anode

Polymer electrolyte

Conducting polymer

ITO electrode

V

Polymer Undoped DopedPolythiophene Red BluePolypyrrole Yellow-green Blue-blackPolyaniline Yellow Green/Blue

On application of voltage

Viewing side

Li anode

Polymer electrolyte

Conducting polymer

ITO electrode

V

Conjugated polymers for nonlinear optics

Polydiacetylene

C

C

C

C C

C

C

C

(

)n

Changes the properties of the light

NLO materials interact with light

Light changes the material properties

Photonic Application of Conducting Polymers - Kerr gate

Laser 2

Laser 1

Polariser CrossedPolariser

NLO ((3)) polymer

Polariser

Laser 1

CrossedPolariser

No light

All organic transistor

Future Outlook

Plastic solar cell based on MDMO-PPV/PCBM(conducting polymer - fullerene composite)

on flexible ITO coated PET

Thank you