www.fluxim.com 1 AC, DC and Transient Characterization of OLEDs M.T.Neukom 1 ,S.Züfle 2 ,J.Sastre 1 ,A.Gentsch 1 ,S.Altazin 1 ,B.Ruhstaller 1,2 1 FluximAG,Winterthur,Switzerland 2 ZurichUniversityofAppliedSciences,InstituteofComputationalPhysics,Winterthur,Switzerland TADFOLEDSummerSchool,May2017,Krutyn,Poland
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www.fluxim.com
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AC, DC and Transient Characterization of OLEDs
M.T. Neukom1, S. Züfle2, J. Sastre1, A. Gentsch1, S. Altazin1, B. Ruhstaller1,2
1Fluxim AG, Winterthur, Switzerland2Zurich University of Applied Sciences, Institute of Computational Physics, Winterthur, Switzerland
TADF OLED Summer School, May 2017, Krutyn, Poland
www.fluxim.com
• Easy-to-use simulation software setfos able to simulate OLEDs and thin film PVs on the small scale/cell level.
• Easy-to-use all-in-one characterization platform paios to extract device and material parameters by dynamic characterization.
• Easy-to-use large-area simulation software laoss able to simulate OLEDs and solar cells up to the module scale.
laoss
R&D Tools for OLEDs & Next Gen PV
www.fluxim.comContent Talk 2
• All‐in‐one measurement platform• Overview of AC, DC and transient measurement techniques for OLEDs
• Case studies with simulation or fitting(polar OLED, MIS‐CELIV, pip)
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www.fluxim.comPaios Research Cycle
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Measured fully automated within a few minutes…
www.fluxim.compaios Measurement Techniques
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Impedance Spectroscopy Capacitance‐Voltage Dark Injection Transients
OLED 2 (T: 247 K – 322 K)Temperature dependent decay
IncreasingTemperature
OLED 1 (T: 230 K – 300 K)Temperature independent decay
www.fluxim.comMotivation: Polar OLED Materials• Decreasing the operating voltage in OLEDs is of primary importance.• This requires high mobility/conductivity ETL layers and well‐matched
energy levels.• Many ETL materials are known to be polar and exhibit spontaneous
molecular dipole orientation1,2,3: Bphen, BCP, Alq3 ... • This leads to charged layer boundaries in the device:
Questions: • Can we determine this
interfacial charge density?• How are the electrical
properties impacted?
1T. D. Schmidt et al., JAP 117, 215502 (2015)2T. Miyamae et al., Chem. Phys. Lett. 616‐617, 86‐90 (2014)3S. Nowy et al., Proc. of SPIE, 7415 (2009)
www.fluxim.comExperiment vs. Simulation
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-10 -8 -6 -4 -2 0 20.5
1
1.5
2
2.5
-10 -8 -6 -4 -2 0 20.5
1
1.5
2
2.5
Voltage (V)
Nor
mal
ized
cap
acita
nce
: 60 nm
: 120 nm
: 240 nm
Alq thickness:
Voltage (V)
Nor
mal
ized
cap
acita
nce
: 60 nm
: 120 nm
: 240 nm
Alq thickness:
SimulationExperiments from [2](a) (b)
CAlq3
Cgeo
CAlq3CAlq3
CAlq3
CAlq3CAlq3
Cgeo
[2] Brütting, W., Berleb, S., Mückl, A. G., “Device physics of organic light‐emitting diodes based on molecular materials”, Org. Elec., 2 (1), 1‐36 (2001).
setfos
S. Altazin et al., Organic Electronics. 39 244‐249 (2016)
www.fluxim.comSimulated OLED Band Diagram
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V<Vt Vt<V<Vbi V>Vbi
setfos
www.fluxim.comStability of (Polar) OLEDs• C‐V responses of polar OLEDs evolve during degradation.• A similar trend can be observed with setfos simulations
diminishing the interface charges.
Interpretation: Orientation polarization isreduced during degradation!
Degradation
C-V measured with PAIOS (TPD/Alq3 bilayer OLED)
C-V simulated with SETFOSfor varying interface charges
Reduction of orientationpolarization
Interfacial charge:
www.fluxim.comStress‐Testing for Degradation Analysis
Perform automated systematic degradation studiesUse current-stress or light-stress
degradation
degradation
S. Züfle et al. Adv. En. Materials (2015) “Areal degradation of OPV cells – experiment & modeling”
photocurrent response to light pulse
un‐encapsulated OPV placed in climate chamber at high T, repeated Paios measurements
www.fluxim.comMobility extraction using CELIV
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t
Voltage
Vtr<V<Vbi
extraction of holes
holes pile up at the HTL/ETL
interface
Polar Alq3 layer prevents electron injection in some voltage range
Using CELIV we are able to determine thehole mobility of the HTL material!
S. Züfle et al., J. Appl. Phys., 2017
www.fluxim.com
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t
Voltage
t
Current
Extract charges with a voltage ramp
Measure mobility, and charge concentration
Mobility extraction using CELIV
tmax: related to the mobility
Extracted charges
0
2
max
2
36.011
32
jjtAd
available with the platform
www.fluxim.com
Hole Mobility from CELIV withpolar OLED
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S. Züfle et al., J. Appl. Phys., 2017“The use of charge extraction by linearly increasing voltage in polar organic light‐emitting diodes”
Consistent with simulation
Determine sheet charge Q
CELIV formulafor Bilayer OLED
www.fluxim.comCELIV with polar layer vs. MIS‐CELIV
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S. Züfle et al., J. Appl. Phys., 2017“The use of charge extraction by linearly increasing voltage in polar organic light‐emitting diodes”
OLED with polar ETL:
MIS structure:
In both cases we have carrier selectivity!
a‐NPD(80 nm)/Alq3(60 nm)
a‐NPD(80 nm)/Ins.(60 nm)
www.fluxim.comLow Temperature Module
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Perform all experiments at temperatures down to 150 Kelvin
www.fluxim.comLow Temperature Module
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Paios Measurement C-V Setfos Calculation C-V
Compare temperature dependent measurement with setfos simulation.
www.fluxim.comThermal Activation in C‐f?
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setfospaios
fr depends on the temperature, activation energy 0.45eV setfos simulation reproduces the paios measurement Injection + transport in HTL is thermally activated
fr=1/RC1
TPD
Alq3
C2
C1
www.fluxim.comSummary
• All‐in‐one comprehensive measurements arepossible and needed for reliable parameterestimation and model validation