<s>
Organic	B-Algorithm
semiconductors	I-Algorithm
are	O
solids	O
whose	O
building	O
blocks	O
are	O
pi-bonded	O
molecules	O
or	O
polymers	B-Language
made	O
up	O
by	O
carbon	O
and	O
hydrogen	O
atoms	O
and	O
–	O
at	O
times	O
–	O
heteroatoms	O
such	O
as	O
nitrogen	O
,	O
sulfur	O
and	O
oxygen	O
.	O
</s>
<s>
In	O
general	O
,	O
they	O
are	O
electrical	O
insulators	O
,	O
but	O
become	O
semiconducting	O
when	O
charges	O
are	O
either	O
injected	O
from	O
appropriate	O
electrodes	O
,	O
upon	O
doping	B-Algorithm
or	O
by	O
photoexcitation	O
.	O
</s>
<s>
They	O
become	O
semiconducting	O
only	O
when	O
charge	O
carriers	O
are	O
either	O
injected	O
from	O
the	O
electrodes	O
or	O
generated	O
by	O
intentional	O
or	O
unintentional	O
doping	B-Algorithm
.	O
</s>
<s>
The	O
reason	O
is	O
that	O
in	O
organic	B-Algorithm
semiconductors	I-Algorithm
their	O
dielectric	O
constants	O
are	O
as	O
low	O
as	O
3	O
–	O
4	O
.	O
</s>
<s>
Efficient	O
photogeneration	O
can	O
only	O
occur	O
in	O
binary	O
systems	O
due	O
to	O
charge	B-Algorithm
transfer	I-Algorithm
between	O
donor	O
and	O
acceptor	O
moieties	O
.	O
</s>
<s>
The	O
optical	O
absorption	O
edge	O
of	O
organic	B-Algorithm
semiconductors	I-Algorithm
is	O
typically	O
1.7	O
–	O
3eV	O
,	O
equivalent	O
to	O
a	O
spectral	O
range	O
from	O
700	O
to	O
400nm	O
(	O
which	O
corresponds	O
to	O
the	O
visible	O
spectrum	O
)	O
.	O
</s>
<s>
The	O
material	O
was	O
probably	O
polyaniline	B-Algorithm
.	O
</s>
<s>
In	O
the	O
1950s	O
,	O
researchers	O
discovered	O
that	O
polycyclic	O
aromatic	O
compounds	O
formed	O
semi-conducting	O
charge-transfer	B-Algorithm
complex	I-Algorithm
salts	O
with	O
halogens	O
.	O
</s>
<s>
The	O
fact	O
that	O
organic	B-Algorithm
semiconductors	I-Algorithm
are	O
,	O
in	O
principle	O
,	O
insulators	O
but	O
become	O
semiconducting	O
when	O
charge	O
carriers	O
are	O
injected	O
from	O
the	O
electrode(s )	O
was	O
discovered	O
by	O
Kallmann	O
and	O
Pope	O
.	O
</s>
<s>
that	O
aromatic	O
hydrocarbons	O
become	O
conductive	O
when	O
blended	O
with	O
molecular	O
iodine	O
because	O
a	O
charge-transfer	B-Algorithm
complex	I-Algorithm
is	O
formed	O
.	O
</s>
<s>
In	O
1972	O
,	O
researchers	O
found	O
metallic	O
conductivity	O
in	O
the	O
charge-transfer	B-Algorithm
complex	I-Algorithm
TTF-TCNQ	B-Algorithm
.	O
</s>
<s>
Superconductivity	O
in	O
charge-transfer	B-Algorithm
complexes	I-Algorithm
was	O
first	O
reported	O
in	O
the	O
Bechgaard	O
salt	O
(	O
TMTSF	O
)	O
2PF6	O
in	O
1980	O
.	O
</s>
<s>
In	O
1973	O
Dr.	O
John	B-Algorithm
McGinness	I-Algorithm
produced	O
the	O
first	O
device	O
incorporating	O
an	O
organic	B-Algorithm
semiconductor	I-Algorithm
.	O
</s>
<s>
The	O
"	O
melanin	O
(	O
polyacetylenes	B-Language
)	O
bistable	O
switch	O
"	O
currently	O
is	O
part	O
of	O
the	O
chips	O
collection	O
of	O
the	O
Smithsonian	O
Institution	O
.	O
</s>
<s>
reported	O
high	O
conductivity	O
in	O
oxidized	O
and	O
iodine-doped	O
polyacetylene	B-Language
.	O
</s>
<s>
They	O
received	O
the	O
2000	O
Nobel	O
prize	O
in	O
Chemistry	O
for	O
"	O
The	O
discovery	O
and	O
development	O
of	O
conductive	B-Algorithm
polymers	I-Algorithm
"	O
.	O
</s>
<s>
Rigid-backbone	O
organic	B-Algorithm
semiconductors	I-Algorithm
are	O
now	O
used	O
as	O
active	O
elements	O
in	O
optoelectronic	O
devices	O
such	O
as	O
organic	B-Device
light-emitting	I-Device
diodes	I-Device
(	O
OLED	B-Device
)	O
,	O
organic	O
solar	O
cells	O
,	O
organic	B-Algorithm
field-effect	I-Algorithm
transistors	I-Algorithm
(	O
OFET	B-Algorithm
)	O
,	O
electrochemical	O
transistors	O
and	O
recently	O
in	O
biosensing	O
applications	O
.	O
</s>
<s>
Organic	B-Algorithm
semiconductors	I-Algorithm
have	O
many	O
advantages	O
,	O
such	O
as	O
easy	O
fabrication	O
,	O
mechanical	O
flexibility	O
,	O
and	O
low	O
cost	O
.	O
</s>
<s>
The	O
discovery	O
by	O
Kallman	O
and	O
Pope	O
paved	O
the	O
way	O
for	O
applying	O
organic	O
solids	O
as	O
active	O
elements	O
in	O
semiconducting	O
electronic	O
devices	O
,	O
such	O
as	O
organic	B-Device
light-emitting	I-Device
diodes	I-Device
(	O
OLEDs	B-Device
)	O
that	O
rely	O
on	O
the	O
recombination	O
of	O
electrons	O
and	O
hole	O
injected	O
from	O
"	O
ohmic	O
"	O
electrodes	O
,	O
i.e.	O
</s>
<s>
The	O
next	O
major	O
step	O
towards	O
the	O
technological	O
exploitation	O
of	O
the	O
phenomenon	O
of	O
electron	O
and	O
hole	O
injection	O
into	O
a	O
non-crystalline	O
organic	B-Algorithm
semiconductor	I-Algorithm
was	O
the	O
work	O
by	O
Tang	O
and	O
Van	O
Slyke	O
.	O
</s>
<s>
Another	O
milestone	O
towards	O
the	O
development	O
of	O
organic	B-Device
light-emitting	I-Device
diodes	I-Device
(	O
OLEDs	B-Device
)	O
was	O
the	O
recognition	O
that	O
also	O
conjugated	O
polymers	B-Language
can	O
be	O
used	O
as	O
active	O
materials	O
.	O
</s>
<s>
The	O
efficiency	O
of	O
OLEDs	B-Device
was	O
greatly	O
improved	O
when	O
realizing	O
that	O
phosphorescent	O
states	O
(	O
triplet	O
excitons	O
)	O
may	O
be	O
used	O
for	O
emission	O
when	O
doping	B-Algorithm
an	O
organic	B-Algorithm
semiconductor	I-Algorithm
matrix	O
with	O
a	O
phosphorescent	O
dye	O
,	O
such	O
as	O
complexes	O
of	O
iridium	O
with	O
strong	O
spin	O
–	O
orbit	O
coupling	O
.	O
</s>
<s>
Doping	B-Algorithm
with	O
strong	O
electron	O
donor	O
or	O
acceptors	O
can	O
render	O
organic	O
solids	O
conductive	O
even	O
in	O
the	O
absence	O
of	O
light	O
.	O
</s>
<s>
Examples	O
are	O
doped	O
polyacetylene	B-Language
and	O
doped	O
light-emitting	O
diodes	O
.	O
</s>
<s>
Today	O
organic	B-Algorithm
semiconductors	I-Algorithm
are	O
used	O
as	O
active	O
elements	O
in	O
organic	B-Device
light-emitting	I-Device
diodes	I-Device
(	O
OLEDs	B-Device
)	O
,	O
organic	O
solar	O
cells	O
(	O
OSCs	O
)	O
and	O
organic	B-Algorithm
field-effect	I-Algorithm
transistors	I-Algorithm
(	O
OFETs	B-Algorithm
)	O
.	O
</s>
<s>
They	O
have	O
been	O
investigated	O
for	O
device	O
applications	O
such	O
as	O
OLEDs	B-Device
,	O
OFETs	B-Algorithm
,	O
and	O
OSCs	O
.	O
</s>
<s>
Molecularly	O
doped	O
polymers	B-Language
are	O
prepared	O
by	O
spreading	O
a	O
film	O
of	O
an	O
electrically	O
inert	O
polymer	B-Language
,	O
e.g.	O
</s>
<s>
In	O
the	O
early	O
days	O
of	O
fundamental	O
research	O
into	O
organic	B-Algorithm
semiconductors	I-Algorithm
the	O
prototypical	O
materials	O
were	O
free-standing	O
single	O
crystals	O
of	O
the	O
acene	O
family	O
,	O
e.g.	O
</s>
<s>
This	O
is	O
of	O
particular	O
advantage	O
for	O
OFET	B-Algorithm
applications	O
.	O
</s>
<s>
</s>
<s>
To	O
design	O
and	O
characterize	O
organic	B-Algorithm
semiconductors	I-Algorithm
used	O
for	O
optoelectronic	O
applications	O
one	O
should	O
first	O
measure	O
the	O
absorption	O
and	O
photoluminescence	O
spectra	O
using	O
commercial	O
instrumentation	O
.	O
</s>
<s>
In	O
contrast	O
to	O
organic	O
crystals	O
investigated	O
in	O
the	O
1960-70s	O
,	O
organic	B-Algorithm
semiconductors	I-Algorithm
that	O
are	O
nowadays	O
used	O
as	O
active	O
media	O
in	O
optoelectronic	O
devices	O
are	O
usually	O
more	O
or	O
less	O
disordered	O
.	O
</s>
<s>
oligomers	O
or	O
segments	O
of	O
a	O
conjugated	O
polymer	B-Language
chain	O
and	O
move	O
by	O
incoherent	O
hopping	O
among	O
adjacent	O
sites	O
with	O
statistically	O
variable	O
energies	O
.	O
</s>
<s>
This	O
disorder	O
effect	O
on	O
charge	O
carrier	O
motion	O
is	O
diminished	O
in	O
organic	B-Algorithm
field-effect	I-Algorithm
transistors	I-Algorithm
because	O
current	O
flow	O
is	O
confined	O
in	O
a	O
thin	O
layer	O
.	O
</s>
<s>
In	O
organic	B-Algorithm
semiconductors	I-Algorithm
charge	O
carriers	O
couple	O
to	O
vibrational	O
modes	O
and	O
are	O
referred	O
to	O
as	O
polarons	O
.	O
</s>
