organic electronics j emyr macdonald, school of physics and astronomy nanophysics group
TRANSCRIPT
Organic Electronics
J Emyr Macdonald,School of Physics and Astronomy
Nanophysics group
Issues
We have had electronics and solar cells made from semiconductors like silicon for years.
• Could we make electronics from molecules or plastic?
• What would the benefits be?– Cheaper than silicon to produce– Flexible sheets
• Has anyone seen solar cells made from molecules? Today?
Nanophysics group
http://www.wbgu.de/wbgu_jg2003_kurz_engl.pdf
World in Transition –Towards Sustainable Energy SystemsGerman Advisory Council on Global ChangeBerlin, 2003
Conductivity = 1 / Resistivity
106
104
102
1 (100)
102
104
106
108
1010
1012
1014
1016
CuFe
polyethylene
Si
cond
ucto
rinsulator
semicon
ductor
(-1cm-1)
Conductivity scale
Energy levels in materials
Electrons can only occupy one level.
The first electron will occupy the lowest energy level. The next electron will have to go into a higher energy level.
many atoms
single atom
electron energy
Energy levels in materials
single atom
many atoms
metal insulator semiconductor
bandgap
electron energy
Conduction in semiconductors
semiconductor
bandgap
• thermal (heat energy)• light
heat
BE k T
light
E hf
cf
wavelength
with
For the semiconductor to conduct we need to provide the electrons with energy greater than the bandgap.
electron energy
bound to atom
free to move
There are two possible sources of energy to excite electron across bandgap:
Conduction in semiconductors
semiconductor
bandgap
• thermal (heat energy)• light
heat
BE k T
light
E hf
cf
wavelength
with
For the semiconductor to conduct we need to provide the electrons with energy greater than the bandgap.
electron energy
bound to atom
free to move
There are two possible sources of energy to excite electron across bandgap:
Conduction in semiconductors
semiconductor
bandgap
• thermal (heat energy)• light
heat
BE k T
light
E hf
cf
wavelength
with
For the semiconductor to conduct we need to provide the electrons with energy greater than the bandgap.
electron energy
bound to atom
free to move
There are two possible sources of energy to excite electron across bandgap:
Demo: effect of wavelength of light
semiconductor
E hf
cf
wavelength
with
electron energy
red
650 nm
violet
470 nm
Semiconductors
Si Si Si Si Si
Si Si Si Si Si
Si
Si Si Si Si Si
Si Si Si Si
Si Si Si Si Si
light
Energy
Semiconductors
Donor
Si Si Si Si Si
Si Si Si Si Si
Si
Si Si Si Si Si
Si Si Si Si
Si Si Si Si Si
As
AsAs
Semiconductors
Si Si Si Si Si
Si Si Si Si Si
Si
Si Si Si Si Si
Si Si Si Si
Si Si Si Si Si
AsB
AsB
Acceptor
Semiconductors
Si Si Si Si Si
Si Si Si Si Si
Si
Si Si Si Si Si
Si Si Si Si
Si Si Si Si Si
What happens when we apply a voltage?
Semiconductors
Si Si Si Si Si
Si Si Si Si Si
Si
Si Si Si Si Si
Si Si Si Si
Si Si Si Si Si
+-
Conductivity = 1 / Resistivity
106
104
102
1 (100)
102
104
106
108
1010
1012
1014
1016
CuFe
polyethylene
Si
{Doped
Si
cond
ucto
rinsulator
semicon
ductor
(-1cm-1)
Conductivity scale
Nobel Prize in Chemistry 2000
“For the Discovery and Development of Conductive Polymers”
Alan HeegerUniversity of California at Santa Barbara
Alan MacDiarmid University of Pennsylvania
Hideki Shirakawa University of Tsukuba
Nobel Prize for Chemistry 2000
How do molecules act as semiconductors?
We must have alternating single and double bonds
We have:• bound electrons between the atoms in the ring
(sp2) • A cloud of partly free electrons above and below
the ring (-electrons)
106
104
102
1 (100)
102
104
106
108
1010
1012
1014
1016
CuFe
polyethylene
Si
{Doped
Si
cond
ucto
rinsulator
semicon
ductor
(-1cm-1)
polymer semiconductors
Conductivity scale
Organic Light-Emitting Diodes
Glass
Cathode (ITO) Conjugated Material
Anode (Al)V
R.H. Friend et al., Nature 397, 121 (1990)
Energy
Organic light-emitting diode (OLED)
Flexible displays
Benefits for Organic Electronics
• Weight• Flexibility• Relatively simple processing• Large areas (displays)• Cost
Disadvantage: Slow compared to silicon
Applications for Molecular Electronics
• Electronic paper
• Low-cost chips (e.g. packaging …)
• Solar energy
• Displays
Solar Cell: demonstration
The plotted voltage is proprtional to light intensity – this is shown vs. time
time
volt
age
Organic solar cell
n
C60PPV
E
n
C60
( )PPV
E
Glass ITO Donor Acceptor Al
Organic solar cell
n
C60
( )PPV
( )
Problem: The exciton can only travel < 20 nm before the electron and hole recombine
E
Glass ITO Donor Acceptor Al
Organic solar cell
n
C60PPV
Need to create exciton <20nm from an interface
Glass ITO Donor Acceptor Al
Organic solar cell
n
C60PPV
E
Glass ITO Donor Acceptor Al
Organic solar cell
C60PPV
+
-
Glass ITO Donor Acceptor Al
Organic solar cell
C60PPV
+
-
Glass ITO Donor Acceptor Al
Organic solar cell
C60PPV
+
-
Glass ITO Donor Acceptor Al
Organic solar cell
Organic Solar Cells
University of Linz
10 x 15 cm ; Active area : 80 cm2
Organic solar cells
Grazing incidence x-ray diffraction
Scanning Probe Microscopy
MDMO-PPV: PCBM blend
P3HT: PCBM blend
Solarmer
Molecular solar cells
Molecular solar cells
Photosynthesis
Photosynthesis: at the molecular level
Summary
• Metals, insulators and semiconductors• Molecules and energy levels• Some new devices made from plastic
electronics• Solar energy and world energy requirements• Current developments in molecular solar cells• Photosynthesis: the oldest and most advanced
solar cell technology
Nanophysics group