The document summarizes research on OLED lighting conducted by Prof. Monkman's OEM Research Group. It discusses how OLED lighting offers better design flexibility compared to traditional lighting. However, two major challenges remain: improving light out-coupling from OLEDs and developing better blue emitter materials that are bright and stable enough. The document also examines the temperature dependence of phosphorescence in polymer films like PVK, providing evidence that monomeric and dimeric ground state species exist.

1. OEM Research Group
OLEDs, the dawn of ultra efficient lighting
Prof Monkman, OEM Research Group
Department of Physics, Durham University
http://www.dur.ac.uk/OEM.group
a.p.monkman@dur.ac.uk

2. Themes
OLEDs, the dawn of ultra efficient lighting
General considerations of making OLED lighting
Problems facing blue phosphorescence
The brave new world of TADF!
Deutsche Bank Berlin
Monkman
OEM Research Group

3. What does OLED lighting offer?
Better design esthetics, better quality of lighting, cheaper to run
‘off grid’ lighting for the third world
We must get away from this
1953
2013
UK strongly engaged with lighting designers and architects and lighting industry
in major UK funded R&D projects
TOPLESS and TOPDRAWER projects

4. What does OLED lighting offer?
Design No No’s
impractical/fanciful
more of the same
welcome to the mental hospital

5. What does OLED lighting offer?
Better Design
Introducing dimensionality
to break up the ceiling space

6. What does OLED lighting offer?
This is now much better Design
Small panels give much higher resolution to the shapes
within a small vertical distance. Very important for design
vital for production yields.
We do not want 1m x 1m panels
And it will be hybrid OLED/LED

7. FP7-224122 – OLED100.eu
D5.7 - Second set of psycho-physiological perception case st
What does OLED lighting offer?
4.2.2.2 “Crater” Gradient
Fabrication/manufacture
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Figure 4.10: Real picture of the light box (right) and luminance distribution pattern with indicated lu
solution/vacuum deposition hybrid processing
profile cross-sections
thus slot die coating for soluble layers
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8. What does OLED lighting offer?
OLED ‘lamps’ being large area surface
emitters have lower glare and so do not
require a luminaire to control brightness
Fluorescent T5 lamps inside
a metal reflector luminaire to
control brightness
The luminaire introduces typical 40% loose of light output, so a 90 lm/W
tube effectively gives a light sources of less than 55 lm/W

9. Inside an OLED
Simple OLED pixel structure
Al (100 nm)
LiF (1 nm)
TPBI (30 nm)
Emissive layer (ca. 70 nm)
PEDOT:PSS (ca. 50 nm)
ITO (125 nm)
Glass
low work function composite metal cathode
electron transport layer ‘ETL’
combined emissive and hole transport layer HTL
transparent anode ‘TCO’
hole injection layer ‘HIL’

10. Inside an OLED
Simple OLED pixel structure
hole injection layer ‘HIL’
Both HTL and ETL
are thick layers via
the use of doping
i.e. p-i-n structure
Schematic energy level diagram of an OLED under bias

11. Inside an OLED
Best commercial white panels from LG Chem
10 cm x 10 cm, 80 lm/W
Complex OLED lighting structure
OLED Stack 1
Charge regeneration layer
MoO3 or TPBi:Cs3PO4
OLED Stack 2
Two stacked OLEDs running at half effective brightness, thus
half drive current required at twice the applied voltage of a single
stack. This improves lifetime by a factor of 4 at high brightness.

12. Inside
prising
mal IL
an OLED
minim
the CG
J. Appl.
p-doped
n-doped
p-doped
n-doped Phys. 111, 103107
CGL technology
time m
IL
IL
good f
(c.) no external bias,
(d.) under reverse bias,
Anode
lifetim
with Al O IL
NPD:MoOwith Al O IL
3
withou
cussed
ferent
alignm
ings. F
p-doped
n-doped
p-doped
n-doped
chemic
IL
IL
leading
of the
(e.) no external bias,
(f.) under reverse bias,
Cathode
with CuPc IL
with CuPcBCP:Cs3PO4
IL
the ene
interfa
FIG. 11. Simplified model of the energy-level alignment for a CGL device
The O3 IL ((c) and (d)) and with CuPc IL electronduced
without IL ((a) and (b)), with Al2CGL under reverse bias generates ((e)
hole bias, (b), (d), and (f.) under by a bias
and
and (f)): (a), (c), and (e) no FIG. 4.pairs which are separated reverseconstant current den
externalVoltage dependency over time atthe bias. field increas
2
he non-stacked (a) reference OLED and the
3
2
3
10 mA/cmintoCGL test devices. The OLED stacks.
was varied b
moves 2 of the two adjacent CuPc IL thickness
0 nm and 8 nm.
Diez et al, J. Appl. Phys., 11, 103107, 2012
The stability of the CGL test device comprisin

13. What challenges remain in OLED lighting?
There are two major current challenges
1) Improve the out-coupling of light from the OLED
Only 22-25% of light escapes from the OLED, current out-coupling
techniques can increase this to nearly 50%. Thus there is still half
the light being lost, getting that light out is a major challenge
2) BLUE – a real materials challenge
The current blue emitters are not blue enough or stable enough.
Host materials have to be extremely high triplet energy which causes
many further problems
New emitter materials and new ways of generating light are needed.

14. Charge Carrier Recombination
e-
h+
recombination
↓
↓
↑
↑
25 % 1P+P-
75 % 3P+P-
↑
↑
25 % Singlet Excitons
↓
↓
75 % Triplet Excitons
None emissive states in purely
organic emitters

15. Light perception
The ‘average’ human eye has poor
sensitivity to blue so it will be hardest
to make a ‘bright’ blue-white lamp.
The eye response shifts to the blue as
intensity diminishes as rods dominate
which are responsive to blue-green only

16. Why is the current blue not good enough?
with FIrpic we will not make
4000K and CRI>80, so its a
non starter.
here, much more blue required, much less red (relative)
so power efficiency must go down
Even a fluorescent tube looses about 40% efficiency to achieve 6200K because of poor blue eye response
Monkman
OEM Research Group

17. Why is the current blue not good enough?
LG Chem say they will mass produce 100x100 mm glass 80 lm/W
4th quarter 2013, 3000K, 75 lm output, 20,000 hrs
note typical fluorescent luminaire is a 3500 lm package
The lighting
industry considers
LT 90 as
standard
Data from
UDC
Monkman
OEM Research Group

18. Why is the current blue not good enough?
Further, FIrpic is unstable to loose of the fluorine atoms, both
on deposition and during operation.
This is also true for any Ir based complex containing fluorine
electron withdrawing groups to blue shift the emission.
Also, for high SOC, the HOMO must contain a significant Ir dorbital content. As the MLCT gap widens (giving bluer
emission) it becomes easier to also populate the dd* states
which very efficiently quench emission. This there are intrinsic
limits on how blue an Ir complex can be pushed whilst
retaining high PLQY
What then might be able to replace an Ir based phosphorescent blue emitter?
Monkman
OEM Research Group

19. Host degradation
Part II
CBP phosphorescence
We did measurements another
Usually people only consider emitter degradation butofthe
sample which was evaporated at the rate between 30-70 angstroms
Very commonly used host
per sec i.e. very high evaporation rate. Normalized delayed fluorescence and phosphorescence
Structure:
hosts, especially high triplet energy host are a various temperatures are shown in figure 15. There are four features of phosphorescence at
problem
spectra at
low temperature and two of them (497nm and 532nm) become more and more insignificant with
increase of temperature as crest at 607 steadily peaks out in relation to the crest at 560.
CBP
d200ms i50ms just after evaporation
d200ms i300ms couple of weeks after evaporation
d200ms i300ms after annealing in air
Other info:
d20msi10ms100K
not annealed, evaporation rate 30 to 70 a per sec, measured just after evaporation
d20msi50ms112K
OSA3251
DCBP, CBP
d20msi70ms110K
Name:
4,4'-Bis(carbazol-9-yl)biphenyl;
sublimed d10msi50ms120K
d20msi10ms135K
Application:
OLED-Hole Transport
d20msi50ms142K
Abs.Max: (nm) 318 nm (Methylene Chloride)14K
0.8
d20ms i10ms
Melting Point(C): 281 (DSC) d20msi70ms270K
DF
0.4
Ph
Intensity, A.U.
Intensity, A.U.
0.8
0.0
400
500
Wavelength, nm
600
700
Formula:
Appearance:
Abbreviation:
0.4
C36H24N2
Odorless pale yellow powder
DCBP, CBP
Sample Preparation:
CBP was evaporated on quartz substrate which before
it was rinsed for 6 minutes with soaped water, deionized
bath. Then it was cured in UV-ozone atmosphere for
Lesker OLED evaporator at the controllable rate. Total
0.0
Spectra recording
Use triplets because they live so long
Gated luminescence measurements were made at the te
that they can sample a large volume and
400
500
600
700
as indicated
Change of spectra without annealing
Wavelength, nm in the figures. Samples were excited with
355nm, at 45 degree angle to the substrate plane. Energ
find the defects, especially at room
falling on the sample was about 1 cm. With the
sides the above changes in phosphorescence spectra we were able to observe the shifted triplet energy reduces markedly oversensitive CCD cam
luminescence was collected with the time
Figure 15
temperature
osphorescence with the peaks only at 560 and 607 without annealing the film just after
aporation (not later than two hours). The results are shown in Figures 19-21. The spectra of this whilst TF increases showing better hopping
Part I
gure 18
Then, after
mple is very similar to the spectra at ~16K of heated films (Figure 17,18), at ~16K of films which couple of weeks (about 9/10 of time sample was held in the compartment near the glove
box the
ectra were recorded after considerable time of evaporation (Figure 12,13,17,18), as well toi.e. it had some exposure to oxygen) the same sample of allmeasure again.fluorescence and shown
First was we measured The results are phosphoresc
CBP ambient evaporation speed hours at 2.5
ectra of unheated films at room temperature (Figure 15). We think this might have somein fig 16-18, red curves. As well this sample was heated infilms. Theatmosphere for twowas about108 angs
relation
were recorded is as shown hours 16-18, green
degrees Celsius and effect on photophysics of heating (annealing)not later than 2in fig after evaporation.
Monkman
the conformation of film. The structure (conformation) which is formed on substrate during /after
OEM Research Group
curves.
aporation should depend on the rate material is cooled. This depends on temperature difference

20. Basic Poly(N-vinylcarbazole)
triplet energy measurements
Mw PVK > 106, high purity
In film ET ~ 2.9 eV
The phosphorescence spectra does
not shift with time implying that the
triplet does not migrate.
Triplet lifetime is also >10 s at 14 K.
Compare to our original pulse radiolysis energy transfer measurements made in benzene
in solution, ET ~ 3 eV.
Pina et al Chemical Physics letters 400, 2004, 441-445
Monkman
OEM Research Group

21. Temperature dependence of
phosphorescence
1.0
Intensity, A.U.
0.8
14 K
0.6
0.4
0.2
ET=2.89 eV
0.0
400
450
500
550
600
650
700
Wavelength, nm
Monkman and Jankus
PHOTONIC MATERIALS CENTRE
70 ms delay
355 nm excitation 150 ps pulse

22. Temperature dependence of
phosphorescence
1.0
Intensity, A.U.
0.8
14 K
44 K
0.6
0.4
0.2
ET=2.55 eV
0.0
400
450
500
550
600
650
700
Wavelength, nm
Monkman
OEM Research Group
70 ms delay
355 nm excitation 150 ps pulse

23. Temperature dependence of
phosphorescence
1.0
Intensity, A.U.
0.8
14 K
44 K
85 K
0.6
0.4
0.2
ET=2.41 eV
0.0
400
450
500
550
600
650
700
Wavelength, nm
Monkman
OEM Research Group
70 ms delay
355 nm excitation 150 ps pulse

24. dilute solution state phosphorescence
Temperature dependence of
phosphorescence
14 K
44 K
14K - 44K
Pina et al Chemical Physics letters 400, 2004, 441-445
Monomeric
ET=2.88 eV
Dimeric
ET=2.4 eV
Jankus and Monkman Adv Func Mat 21, 3350, 2011
Monkman
OEM Research Group

25. in toluene
450 nm excitation
0 .04 m g /m l
0 .4 m g /m l
4 m g /m l
3 8 m g /m l
0 .2
0 .1
1.0
ET=2.41 eV
0.8
Inte ns ity, A .U .
O pt c a l de ns ity
Is this a ground state or excited state species?
0.6
0.4
0.2
0 .0
350
400
45 0
W a veleng th, nm
500
Clear concentration dependent
ground state absorption.
Monkman
400
450
500
5 50
6 00
W a veleng th, nm
6 50
Emission at 12us delay, 450 nm excitation
at 14 K, identical to dimeric species emission
NB, good vibronic structure
OEM Research Group

26. Evidence for two ground state species
Excitation 450 nm
14 K
44 K
85 K
100 K
295 K
Intensity, A.U.
1
6650 ns and 22520 ns
4980 ns and 8850 ns
2640 ns
2190 ns
980 ns
Very clearly these species
are monomer and dimer
they are NOT ‘excimer’
0.1
0.01
0
10000
20000
30000
Time, ns
Two distinct lifetime components which are highly temperature dependent
Monkman
OEM Research Group

27. What form has the dimer?
½ co-facial dimer
Benten et al, J.Phys.Chem.B
2007, 111, 10905
Full co-facial dimer
The closer the co-facial interaction between neighboring carbazole units the
larger the shift in the phosphorescence. Further, the shift is so large that these
dimers must have substantial charge transfer character.
Monkman
OEM Research Group

28. What could replace Ir ?
We need new blue emitters
that combine the stability of a
fluorescence molecule with
the an ability to ‘harvest’
triplet excitons very efficiently
Is this fundamentally impossible?
Monkman
OEM Research Group

29. E-type delayed fluorescence to harvest triplet excitons
TADF = E-type DF
!"##$%& $'( )"*+,,-
e-
:
h+
Thermally activated
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Delayed
Fluorescence
(TADF)
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singlet state conversion," Nature Photonics, vol. 6, pp. 253-258, Apr
2012.
Ground
State
Monkman
OEM Research Group

30. Introduction
&'()*+%,-$'%./,%("#$$%!EST%
Basic theory of CT states
!"#$!%&!'()*+
!,#$!%&!'(&*
&'()*+%,-$'%./,%("#$$%!theST%
K, E exchange energy
EH :HOMO Energy
EL : LUMO Energy
K :Exchange Energy
dependents on the spatial
!EST=2K
separation of the orbitals and
Energy
!"#$!%&!'()*+ EH ::HOMO Energy
LUMO
!EST=2K
1 &! (&* EL :Exchange Energy the overlap of the HOMO and
!,#$!%! ' ! (1)d" d"
K
K = !L (1)!U (2)
LUMO in this case
L (2) U
1
2
r12
1
K = ## !L (1)!U (2) !L (2)!U (1)d" 1d" 2
r12
(LUMO)
(HOMO)
(LUMO)
##
(HOMO)
(HOMO)
・0#,*'%!EST
(LUMO)
・0#,*'%!EST
(HOMO)
・ !"#$$%!EST
(LUMO)
・ !"#$$%!EST
The trade off, if HOMO and LUMO have zero overlap the radiative decay rate becomes
Donor
X
Donor state has Acceptor unless Acceptor
X
very small so the CT
low PLQY
the lifetime is long i.e. IC and NR decay
! Donor-Acceptor backbone
are even weaker.
! Donor-Acceptor backbone
! X:Introduction of steric hindrance
! X:Introduction of steric hindrance
! Rather high radiative decay rate
! Rather high radiative decay rate
Monkman
OEM Research Group

31. TADF
New family of D-A-D molecules incorporating para and meta D-A coupling so we call
systems containing 1 ‘linear’ and 2 ‘bent’ based on the electron transport unit
dibenzothiophene-S,S-dioxide developed in Durham
Dias et al., J.Phys.Chem.B. 110, 19329, 2006
ST energy splitting from 0.35 to 0.9 eV
1d
Dias and Monkman et al., Adv. Mater. 2013, 25, 3707
Monkman
OEM Research Group

32. TADF
Intramolecular Charge Transfer States
(ICT)
D
2b
D
A
carbazole donors
dibenzothiophene-S,S-dioxde
acceptor
HOMO
hν
LUMO
Small singlet-triplet energy splitting
in CT states
Singlet state
Ground and excited state orbitals
are nearly independent with very little
orbital overlap. This is important.
But also gives low radiative decay rate
1ICT
3ICT
ΔE (1CT-3CT)<100 meV
Triplet state
ΔEST∼ 0.3 to 0.9 eV
Dias et al., J. Phys. Chem. B 2006, 110, 19329-19339
K. Moss et al., J. Org. Chem. 2010, 75, 6771–6781
Monkman
OEM Research Group

33. Delayed Fluorescence measurements
8
Intensity, A.U.
10
pe 1
- slo
PF
7
10
1
lope
P H -s
6
10
DF
5
10
a)
Laser pulse energy, µJ
1
prompt
emission measured
at 450 nm
delayed
0
1
2
3
4
5
6
7
8
9
10 10 10 10 10 10 10 10 10 10
Time, ns
Normalized intensity, A.U.
Intensity, A.U.
0
10
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
-7
10
-8
10
-9
10
-10
10
-11
10
0.1
-
e2
lop
s
3.6 µJ
0.1 µJ
0.8
150 ps Nd:YAG (70 mJ @ 355 nm)
200 ps FWHM gated iCCD
HP pulse generator FWHM 10 ns
0.4
0.0
b)
400
450
500 550 600
Wavelength, nm
650
Rothe, Monkman Phys.Rev.B (2002), Rothe et al Chem.Phys. (2002), Sinha et al Phys.Rev.Lett (2003)
Monkman
OEM Research Group

34. TADF
Enhanced CT character for bent materials (2’s)
2c
D
D
A
ΔE /Δf= 0.91
ΔE
(e V )
0 .8
hν
0 .4
1 .2
2e
2d
Lippert-Mataga
0 .4
plots
0 .0
0 .8
HOMO
ΔE /Δf= 2.47
ΔE /Δf= 1.55
0 .1
0 .2
0 .3
0 .4 0 .0
Δf
Monkman
ΔE /Δf= 1.01
1b
LUMO
1e
1 .2
OEM Research Group
0 .1
0 .2
0 .3
0 .4

35. Fluorescence lifetimes
8
1d
he x a ne
λx :3 6 3 nm
λx :4 2 0 nm
6
he x a ne
λx :
3 6 3
nm
λe m :
4 1 0
nm
6
τ:
3.08
ns
4
2
1d
2d
3
C ounts x 1 0
3
8
C ounts x 1 0
TADF
IR F :
2 1
ps
0
0
1
2
3
4
T im e
(ns )
5
4
τ1 :
1.60
ns
2
0
6
2d
IR F :
2 1
ps
0
2
4
T im e
(ns )
6
8
The CT character is not responsible for the observation of strong Phosphorescence
80
290K
100K
60
RT
Phosphorescence
6
40
2 .0
2d
in
z eo n ex
ΔEST=0.46 eV
6
4a
Inte ns ityx 1 0
(c ps )
200
ΔEST=1.1 eV
500
600
T 290K
T 270K
T 250K
T 200K
T 150K
T 100K
T 80K
160
120
80
N o
O 2
1 .6
1 .2
0 .8
with
O 2
0 .4
0 .0
400
450
500
550
600
wa ve le ng th
(nm )
40
0
300
6
400
0
Inte ns ity
x 1 0
(c ps )
20
Inte ns ityx 1 0
(c ps )
5d
Lone pairs are important
400
500
W a ve le ng th
(nm )
Monkman
600
Dias and Monkman et al., Adv. Mater. 2013, 25, 3707
OEM Research Group

36. TADF
Properties of delayed fluorescence (DF)
4a
2
4a
barrier to viscous flow
in ethanol is 0.15 eV
6
D F
inte g ra lx 1 0
(c ounts )
10
Pure Triplet Fusion
ΔEST=1.1 eV
E a = 0.16 ±0.05
e V
10
1b
1
10
0
3.0
3.2
3.4
10
2
10
E a = 0.18 ±0.05
e V
10
N orm .
Inte ns ity
A .U .
1b
6
D F
inte g ra lx 1 0
(c ounts )
3
10
-­‐7
-­‐9
1ππ*
3.5
4.0
4.5
-­‐1
10 /T
(K )
5.0
10
3
Dias and Monkman et al., Adv. Mater. 2013, 25, 3707
Monkman
3.26 eV
1CT*
3.12 eV
3ππ*
1
3.0
P rom pt
(7 .4 1
ns )
-­‐5
10
DF I2
3
-­‐3
10
4.2
1b
-­‐1
10
4.0
10 /T
1
10
10
3.8
ΔEST=0.84 eV
3.6
-­‐1 1
10
-­‐1 0
10
-­‐8
10
-­‐6
10
-­‐4
10
ΔEST=0.84 eV
2.28 eV
T A D F (bi
e x pone ntia l)
378
µs
(6 7 % ),
1.8
m s
(3 3 % )
-­‐2
T im e
(ns )
OEM Research Group
3CT*

37. Properties of delayed fluorescence (DF)
2.95 eV
1CT*
2.74 eV
3ππ*
ΔEST=0.63 eV
3CT*
ΔEST=0.63 eV
2.11 eV
1
-­‐7
10
2
1e
10
1
10
2
240K
D F /P F
:
0 .0 0 2 8
10
E a = 0.26 ±0.02e V
ΔE S T = 0.63
e V
-­‐9
T A D F
(487
µs )
-­‐5
10
1e
ΔE S T = 0 .6 3 ±0 .0 6
e V
10
-­‐1 1
-­‐1 0
-­‐9
-­‐8
-­‐7
-­‐6
-­‐5
-­‐4
-­‐3
-­‐2
10 10 10 10 10 10 10 10 10 10
-­‐1
700
6
10
10
-­‐3
6
10
N orm .
Inte ns ity
A .U .
-­‐1
600
3
D F
inte g ra l
v s
e x c ita tion
dos e
R T ,
e tO H
P rom pt
(8.66
ns )
10
500
wa ve le ng th
(nm )
3
1e
E m is s ion
Inte g ra lx 1 0
(c ounts )
10
S S -­‐R T
T A D F -­‐3 0 0 K
T A D F -­‐2 0 0 K
400
We observe TADF with a ST energy gap of 0.63 eV!
10
1e
1ππ*
N orm a liz e d
Inte ns ity
(a .u.)
1e
Mixed Triplet Fusion TADF
D F -­‐inte g ra lx 1 0
(c ounts )
TADF
10
0
10
line a r
fit
with
s lope
fix e d
a t
2
(c oe f.
c orr.
0.995)
0
T im e
(s )
10
1
10
2
10
3
10
1
P owe r
( µJ )
Monkman
OEM Research Group
2 .5 3 .0 3 .5 4 .0 4 .5 5 .0 5 .5
3
-­‐1
10 /T
(K )

38. TADF
Properties of delayed fluorescence (DF)
2e
ΔEST=0.48 eV
3CT*
ΔEST=0.48 eV
2.39 eV
0 .8
0 .4
0 .0
400
We observe strong TADF with an energy gap of 0.48 eV!
10
4
2e
10
-­‐4
10
-­‐6
10
3
T A D F
( 818
µs )
-­‐8
-­‐1 0
-­‐9
-­‐8
-­‐7
-­‐6
-­‐5
-­‐4
-­‐3
-­‐2
10 10 10 10 10 10 10 10 10 10
-­‐1
700
W a ve le ng th
(nm )
4
E a = 0.28 ±0.02e V
ΔE S T = 0.48
e V
ΔE S T = 0 .4 8 ±0 .0 6
e V
10
3
10
2
6
10
2
10
1
240K
line a r
fit
with
s lope
fix e d
a t
1
c oe f
c orre l:
0.996
D F /P F :0 .0 2 6
-­‐1 0
600
-­‐2
10
500
2e
D F
Inte g ra l
a s
a
func tion
of
e x c ita tion
powe r
R T ,
e tO H
6
10
P rom pt
(3.07
ns )
N orm .
Inte ns ity
A .U .
0
E m is s ion
Inte g ra lx 1 0
(c ounts )
2e
10
10
D F -­‐Inte g ra lx 1 0
(c ounts )
10
2
S te a dy-­‐S ta te
T A D F
2e
2.87 eV
N orm a liz e d
Inte ns ity
(a .u.)
1CT*
3ππ*
1 .2
3.15 eV
1ππ*
10
Dominant TADF
10
0
T im e
(s )
10
1
10
2
10
3
10
1
2 .5
P owe r
( µJ )
Monkman
OEM Research Group
3 .0
3 .5
4 .0
3
4 .5
-­‐1
10 /T
(K )
5 .0
5 .5

39. TADF
Constant acceptor
1e
2e
2d
ΔE
ΔE S T = 0.48 ±0.05
e V
= 0.63 ±0.06
e V
ST
E a = 0.26 ±0.02e V
ΔE S T = 0.35 ±0.04
e V
E a = 0.28 ±0.02
e V
E a = 0.28 ±0.02e V
Activation energy is
independent of the ST
gap and is not due to
viscous flow
2
3
10
2d
2e
10
6
D F -­‐inte g ra lx 10
(c ounts )
4
1 0 1e
240
K
10
1
240
K
240
K
3
4
5
3
4
3
5
4
5
-­‐1
1 0 /T (K )
Monkman
3
Dias and Monkman et al., Adv. Mater. 2013, 25, 3707
OEM Research Group

40. TADF
Constant donor
2d
3d
4d
ΔE S T = 0.57 ±0.05e V
ΔE S T = 0.35 ±0.04
e V
E a = 0.83 ±0.02
e V
Activation energy is
dependent on the
donor structure
ie. lone pairs
2
3
10
ΔE S T = 0.87 ±0.04
e V
E a = 0.47 ±0.03e V
E a = 0.28 ±0.02
e V
10
4d
3d
6
D F -­‐inte g ra lx 10
( c ounts )
4
1 0 2d
280
K
240
K
10
260
K
1
3
4
5
3
4
5
1 0 3 /T (K -­‐1 )
Monkman
3
4
5
Dias and Monkman et al., Adv. Mater. 2013, 25, 3707
OEM Research Group

41. TADF
We require another energy level to explain the temperature dependent behaviour of the DF
1e
2e
1ππ*
1CT*
1ππ*
2.95 eV
2.74 eV
3CT*
ΔEST=0.63 eV
3ππ*
ΔE=0.35 eV
2.11 eV
Large gap TF dominates
Monkman
2.87 eV
1CT*
3CT*
ΔEST=0.28 eV
ΔEST=0.48 eV
ΔEST=0.28 eV
3.15 eV
3ππ*
ΔE=0.2 eV
2.39 eV
Small gap TADF
dominates
OEM Research Group

42. TADF
We introduce the “little known” nπ* orbital
Dias and Monkman et al., Adv. Mater. 2013, 25, 3707
Monkman
OEM Research Group

43. How efficient is TADF even with a gap of 0.36 eV
10
DF/PF ratio∼ 5%
400
2
T A D F
s te a dy-­‐s ta te
e m is s ion
500
600
700
10
1
10
line a r
fit
with
s lope
fix e d
a t
1.
c oe f.
c orre l.:
0.995
0
10
0
10
ΦT = 0.05 ±0.01
10
10
-­‐6
2
10
600
4
400
200K
2
-­‐8
200
D F /P F :
0.048
10
3
6
800
T A D F
(230
µs )
-­‐1
330K
6
100%
efficient
TADF
Inte ns ity x 10
(c ps )
-­‐4
9
k is c = (5 ±1)x 10
s
6
-­‐2
10
10
ΔE T A D F = 0.38 ±0.05
e V
-­‐T
10
1
2d
P rom pt
(4.7
ns )
N orm
Inte ns ity
A .U .
2
Triplet yield ∼ 5%
1 0 0 0
0
10
powe r
( µJ )
8
10
2d
wa ve le ng th
(nm )
2d
3
2d
2d
10
E m is s ion
Inte g ra l
(c ounts )
N orm a liz e d
Inte ns ity
(a .u,)
E m is s ion
Inte g ra lx 10
(c ounts )
TADF
-­‐1 0
10
-­‐1 0
-­‐9
-­‐8
-­‐7
-­‐6
-­‐5
-­‐4
-­‐3
10 10 10 10 10 10 10 10
-­‐2
0
400
T im e
(s )
500
600
700
wa ve le ng th
(nm )
Dias and Monkman et al., Adv. Mater. 2013, 25, 3707
Monkman
0
200 220 240 260 280 300 320 340
T e m pe ra ture
(K )
M. N. Berberan-Santos, J. M. M. Garcia, JACS. 1996, 118, 9391
OEM Research Group

44. 0.8
Neat 2d Film
0.4
1.0
0.8
0.6
0.4
0.2
400 450 500 550 600 650 700
Wavelength, nm
500
600
Wavelength, nm
Excitation pulse
energy in microjouls
2d in TPBi
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
700
0.130mkJ
1.061mkJ
2.32mkJ
7.36mkJ
7.94mkJ
2d in TAPC Excitation pulse
energy in microjouls
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
0.063mkJ
0.205mkJ
1.09mkJ
4.16mkJ
350 400 450 500 550 600 650 700
Wavelength, nm
350 400 450 500 550 600 650 700
Wavelength, nm
2d in TAPC - TADF dominated
1,3CT
In TAPC no
host quenching
TADF PLQY 0.5
In TPBi 2d TF dominates with a small
TADF component
Integrated intensity, A.U.
2
Critical role of host triplet energy
10
1
10
0
10
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
2d in TPBi red edgesmaller TF influence
1.29
1.17
1.05
1.04
neat 2d red
edge
TADF
dominated
-2
Monkman
2d in TPBi blue edgestrong TF influence
1.09
10
Jankus et al,. PRL in press
Excitation pulse
energy in microjouls
0.170mkJ
0.776mkJ
1.2mkJ
4.75mkJ
9.1mkJ
15.6
50mkJ
0.0
0.0
400
Normalized intensity, A.U.
2d
neat
in TPBi
in TAPC
Normalized intensity, A.U.
Normalized intensity, A. U.
14 %
8%
50%
Normalized intensity, A.U.
TADF in solid state
PLQY
1.87
-1
10
0
neat 2d blue edge TF
dominated
1
10
10
Pulse fluence, µJ
OEM Research Group
2
10

45. TADF in solid state
Critical role of host triplet energy
Normalized intensity, A.U.
In TAPC no 1,3CT host quenching
TADF PLQY 0.5
So TAPC is special as all excitations remain trapped on the 2d
thus we find much longer lifetimes of excited states
433 ns for the prompt emission
25 us for TADF and 165 us for phosphorescence
We also find that the first and last decay components decrease
with increasing temperature whereas the middle one increases
with increasing temperature
DF/PF~0.082
2d neat film
7pc 2d in TAPCDF/PF~1.8
7pc 2d in TPBi DF/PF~0.15
2d in solution DF/PF=0.048
0
10
-2
10
-4
10
-6
10
-8
10
0
10
1
10
2
3
4
10 10 10
Time, ns
5
10
6
DF/PF ratio of 1.8
the triplet yield is 64%
and the fluorescence yield is 50%
This signifies long CT lifetimes yielding high
triplet CT production, energy cycling
between the iso energetic CT states and thermal
activation from the ππ* triplet to the 3CT
10
Monkman
OEM Research Group

46. TADF devices
How do OLEDs performed
based on TADF emitters?
Monkman
OEM Research Group

47. Phosphorescence
TADF devices
b
N
10
CN
CN 300 K
200 K
100 K
N
NC
0
N
R
1
300 K N
R
N
N
R
CN
R
4CzIPN
10
Prompt
R
Delayed
N
N
10–1
bazolyl
–2
R
R
4CzTPN: R = H
4CzTPN-Me: R = Me
4CzTPN-Ph: R = Ph
Photoluminescence quantum efficiency
gy 10
diagram and molecular structures0of CDCBs. a, Energy
400
500
600
0
10
20
30
40
ventional organic molecule. b, Molecular structures of CDCBs.
Time (μs)
phenyl.
c
d
–3
14.2
1.0
ΔEST = 83
Combined
n. 2International Institute for Carbon Neutral Energy Research (WPI-I2CNER), meV
0.9
14.0
Prompt
Delayed
0.8
101
100
10–1
Normalized electroluminescence
intensity (a.u.)
Normalized photoluminescence intensity
a
R
External electroluminescence quantum efficiency (%)
LETTER RESEARCH
1
4CzIPN
4CzTPN-Ph
2CzPN
0
400
10–2
10–3
500
600
Wavelength (nm)
10–2
10–1
700
100
101
102
For a green device 13.6
using 4CzTPN
Current density (mA cm )
0.6
devices having EQE of 19% have been
Figure 5 | Performance of OLEDs containing CDCB derivatives. External
13.4
reserved
0.5
13.2
electroluminescence quantum efficiency as a function of current density for
reported. This equates to an internal
0.4
OLEDs containing 4CzIPN (green circles; error within 1.5%), 4CzTPN-Ph (red
13.0
0.3
QE approaching 85%, as good as phosphorescent
1.0%) and 2CzPN (blue triangles; error within 1.0%) as
triangles; error within
12.8
0.2
emitters. Inset, electroluminescence spectra of the same OLEDs (coloured
12.6
OLED all from TADF
accordingly) at a current density of 10 mA cm22.
0.1
13.8
–2
In(kRISC)
0.7
0.0
12.4
0
50
100 150 200
Temperature (K)
250
300
3.5
4.0
4.5
–3/T (K–1)
10
5.0
Figure 4 | Temperature dependence of photoluminescence characteristics
of a 5 6 1 wt% 4CzIPN:CBP film. a, Photoluminescence decay curves of a
wt% 4CzIPN:CBP film at 300 K (black line), 200 K (red line) and 100 K (blue
Monkman
ine). The photoluminescence decay curves show integrated 4CzIPN emission.
The excitation wavelength of the films was 337 nm. b, Photoluminescence
Adachi et al, Nature, 492, 237, 2012
11.2 6 1% and 8.0 6 1%, respectively, which are also higher than those
of conventional fluorescence-based OLEDs.
Finally, we consider the mechanism that drives such efficient reverse
ISC without heavy metals. It is generally accepted that the introduction
of spin–orbit coupling provided by heavy atoms is required for both
OEM Research Group
ISC and reverse ISC to be efficient. Thus, metal complexes containing

48. OLED Lighting, a bright future
Cost no object
Designed by
Kardorff
Deutsche Bank
Berlin

49. OLED Lighting, a bright future
Cost no object
Designed by
Kardorff
Deutsche Bank
Berlin

50. OEM Research Group
Blue is always a problem for any system
Phosphorescent emitters are difficult to push blue enough
High triplet hosts suffer major degradation problem
Triplet Fusion not good enough, 62.5% maximum not attainable
TADF promising, true 100% triplet harvesting
ICT again has host problem
DA exciplex being a self ambipolar host is really exciting
The TOPLESS
lamp.
Thank you
http://www.dur.ac.uk/OEM.group
a.p.monkman@dur.ac.uk