<s>
Phosphorescent	B-Algorithm
organic	I-Algorithm
light-emitting	I-Algorithm
diodes	I-Algorithm
(	O
PHOLED	B-Algorithm
)	O
are	O
a	O
type	O
of	O
organic	B-Device
light-emitting	I-Device
diode	I-Device
(	O
OLED	B-Device
)	O
that	O
use	O
the	O
principle	O
of	O
phosphorescence	O
to	O
obtain	O
higher	O
internal	O
efficiencies	O
than	O
fluorescent	O
OLEDs	B-Device
.	O
</s>
<s>
Like	O
all	O
types	O
of	O
OLED	B-Device
,	O
phosphorescent	O
OLEDs	B-Device
emit	O
light	O
due	O
to	O
the	O
electroluminescence	O
of	O
an	O
organic	B-Algorithm
semiconductor	I-Algorithm
layer	O
in	O
an	O
electric	O
current	O
.	O
</s>
<s>
In	O
OLEDs	B-Device
using	O
fluorescent	O
organic	O
molecules	O
only	O
,	O
the	O
decay	O
of	O
triplet	O
excitons	O
is	O
quantum	O
mechanically	O
forbidden	O
by	O
selection	O
rules	O
,	O
meaning	O
that	O
the	O
lifetime	O
of	O
triplet	O
excitons	O
is	O
long	O
and	O
phosphorescence	O
is	O
not	O
readily	O
observed	O
.	O
</s>
<s>
Hence	O
it	O
would	O
be	O
expected	O
that	O
in	O
fluorescent	O
OLEDs	B-Device
only	O
the	O
formation	O
of	O
singlet	O
excitons	O
results	O
in	O
the	O
emission	O
of	O
useful	O
radiation	O
,	O
placing	O
a	O
theoretical	O
limit	O
on	O
the	O
internal	O
quantum	O
efficiency	O
(	O
the	O
percentage	O
of	O
excitons	O
formed	O
that	O
result	O
in	O
emission	O
of	O
a	O
photon	O
)	O
of	O
25%	O
.	O
</s>
<s>
However	O
,	O
phosphorescent	O
OLEDs	B-Device
generate	O
light	O
from	O
both	O
triplet	O
and	O
singlet	O
excitons	O
,	O
allowing	O
the	O
internal	O
quantum	O
efficiency	O
of	O
such	O
devices	O
to	O
reach	O
nearly	O
100%	O
.	O
</s>
<s>
Due	O
to	O
their	O
potentially	O
high	O
level	O
of	O
energy	O
efficiency	O
,	O
even	O
when	O
compared	O
to	O
other	O
OLEDs	B-Device
,	O
PHOLEDs	B-Algorithm
are	O
being	O
studied	O
for	O
potential	O
use	O
in	O
large-screen	O
displays	O
such	O
as	O
computer	O
monitors	O
or	O
television	O
screens	O
,	O
as	O
well	O
as	O
general	O
lighting	O
needs	O
.	O
</s>
<s>
One	O
potential	O
use	O
of	O
PHOLEDs	B-Algorithm
as	O
lighting	O
devices	O
is	O
to	O
cover	O
walls	O
with	O
large	O
area	O
PHOLED	B-Algorithm
light	O
panels	O
.	O
</s>
<s>
The	O
United	O
States	O
Department	O
of	O
Energy	O
has	O
recognized	O
the	O
potential	O
for	O
massive	O
energy	O
savings	O
via	O
the	O
use	O
of	O
this	O
technology	O
and	O
therefore	O
has	O
awarded	O
$	O
200,000	O
USD	O
in	O
contracts	O
to	O
develop	O
PHOLED	B-Algorithm
products	O
for	O
general	O
lighting	O
applications	O
.	O
</s>
<s>
One	O
problem	O
that	O
currently	O
hampers	O
the	O
widespread	O
adoption	O
of	O
this	O
highly	O
energy	O
efficient	O
technology	O
is	O
that	O
the	O
average	O
lifetimes	O
of	O
red	O
and	O
green	O
PHOLEDs	B-Algorithm
are	O
often	O
tens	O
of	O
thousands	O
of	O
hours	O
longer	O
than	O
those	O
of	O
blue	O
PHOLEDs	B-Algorithm
.	O
</s>
