Modeling organic electronics with ADF

Copyright © 2014, SCM.
Modeling Organic Electronics with ADF
1) OLEDs: phosphorescence
2) Charge mobility (e.g. OFETs)
3) PVs/DSSC: singlet fission,
excitation, e- injection, regeneration
published papers & unpublished calcs by Mr. Mori, Ryoka Inc.
http://www.scm.com/OrganicElectronics

Hartmut YersinHartmut YersinHartmut Yersin
Y. Suzuri et al., Sci. Technol. Adv. Mater. 15 (2014) 054202. doi:10.1088/1468-6996/15/5/054202
Organic Light-Emitting Diodes
Challenges:
• Optimize triplet phosphorescence rate
• Minimize triplet-triplet annihilation and triplet-polaron quenching
• Optimize properties of host material (higher T energy)
• Optimize mobility in electron / hole transport layers
• Optimize out-coupling

Phosphorescent OLED emitters:
SOC-TDDFT with solvation compares well with Expt.
K. Mori, T. P. M. Goumans, E. van Lenthe, F. Wang, Phys. Chem. Chem. Phys. 16, 14523 (2014)

Predicting phosphorescent rates of Ir(III) complexes
Best correlation with pSOC, a
pragmatic approach:
TD-B3LYP/TZP/DZP//BP86/TZ2P/TZP
J. M. Younker and K. D. Dobbs, Correlating Experimental Photophysical Properties of Iridium(III) Complexes to Spin−Orbit Coupled
TDDFT Predictions, J. Phys. Chem. C, 117, 25714-25723 (2013)

Vibronic fine structure OLED phosphor Pt complex:
vibrational progression from T1 → S0 emission
Courtesy of Mr. Kento Mori, Ryoka, unpublished results
unpublished calcs by Mr. Mori, Ryoka Inc. on TSUBAME2.0, JACI

h+
Methods to calculate charge mobilities
• Hopping transport:
– Charge transfer integrals + other elements, directly printed
– Electronic couplings from frozen-density embedding
• Band transport: effective mass tensors in BAND
• Non-equilibrium Green’s Function (NEGF)
– transmission probabilities for single-molecule junctions
– quick calculation: wide-band limit
– also in BAND (periodic structures) and in DFTB (large systems)
Q

Hole / electron mobilities
• Ordered crystals (low T) => band-like transport
• Amorphous materials: incoherent hopping
• Accoustic deformation potential
   1
 me    



kk
m


 k2
2
1 1



i
i
i
i
k
k
P
mc: the effective mass along the direction of transport
md: the density of states mass, (ma mb)1/2
ac: the acoustic deformation potential, V dEvbm/dV
B: the elastic modulus
Leff: the length of the p-bonded core of the molecule
  dcBac
eff
mmTk
BLe
2
3





Effective transfer integral Jeff = electronic coupling V
• Definition of fragments • Matrix elements from ADF
C2
HOMOks
C1
HOMORP  hJ 
C2
HOMO
C1
HOMORP S
C1
HOMOks
C1
HOMORR  hH 
C2
HOMOks
C2
HOMOPP  hH 
extract dimer
Fragment C1
Fragment C2
Molecular crystal of pentacene
(a) “transfer integral”
(b) spatial overlap
(c) site energy
 
2
RP
PPRRRPRP
1
2/
S
HHSJ
V



orthogonalization

Anisotropic hole mobilities in pentacene
S.-H. Wen et al., J. Phys. Chem. B 113, 8813 (2009)
Anisotropic mobility：

Oligofuran vs Oligothiophene
6F:  17 times
larger than 6T
J.-D. Huang, S.-H. Wen, W.-Q. Deng, K.-L. Han, Simulation of Hole Mobility in α-Oligofuran Crystals. J. Phys. Chem. B 115, 2140-2147 (2011)

Hole transport in tetrathienoarenes
Y.-A. Duan et al., Organic Electronics 15, 602-613 (2014)

Transport in N-hetero-pentacenes
X.-K. Chen et al., Organic Electronics 13, 2832-2842 (2012)

Transport in ladder-type molecules
H.-L. Wei, Y.-F. Liu, Appl. Phys. A, in press(2014)

Environment effects: transport in 1D wires
A. A. Kocherzhenko et al., Effects of the Environment on Charge Transport in Molecular Wires, J. Phys. Chem. C. 116 25213-25225 (2012).
hybrid quantum-classical model with
polarizable force field
including dynamic and static disorder

Electronic couplings + environment with FDE:
charge transfer, exciton, charge separation
Pavanello/Rutgers & Neugebauer/Muenster groups: Excitons: J. Chem. Phys. 138, 034104 (2013),
long range charge separation: J. Chem. Phys. 140, 164103 (2014),
charge transfer: J. Chem. Theory Comput. 2014, 10, 2546−2556
Linear scaling, environment response, constrain charge, excitation, spin, ...

Environment effects: frozen-density embedding
M. Pavanello, T. van Voorhis, L. Visscher, and J. Neugebauer, An accurate and linear-scaling
method for calculating charge-transfer excitation energies and diabatic couplings, J. Chem. Phys.
138, 054101 (2013).
N C2H4 V 12 ΔE ex
2 … …
4 0.261 0.540
6 0.260 0.521
8 0.261 0.534
10 0.260 0.538
20 0.260 0.534
Scales linearly with number of molecules included in environment
Effect on couplings and excitation energy larger for more polar systems

Exciton couplings with frozen-density embedding
C. König et al., Direct determination of exciton couplings from
subsystem time-dependent density-functional theory within the
Tamm-Dancoff approximation, J. Chem. Phys. 138, 034104 (2013).
C. König and J. Neugebauer, Exciton Coupling Mechanisms
Analyzed with Subsystem TDDFT: Direct vs. Pseudo Exchange
Effects, J. Phys. Chem. B 117, 3480 (2013).

Band Transport
• Drude model [J. Phys. Chem. C 114, 10592 (2010)]
• Acoustic deformation potential model [Appl. Phys. Lett. 99, 062111
(2011)]
mc: the effective mass along the direction of transport
md: the density of states mass, (ma mb)1/2
ac: the acoustic deformation potential, V dEvbm/dV
B: the elastic modulus
Leff: the length of the p-bonded core of the molecule
   1
 me
  dcBac
eff
mmTk
BLe
2
3




   



kk
m


 k2
2
1 1

: the mean relaxation time of the band state
m: the effective mass of the charge carrier,

hopping transport (P, T1, T2) band transport (a, b) experiment
l (eV) V (eV)  (cm2
V-1
s-1
) m/m0  (cm2
V-1
s-1
)  (cm2
V-1
s-1
)
Rubrene 0.1460 -0.082 7.22 0.99 36 20-40a
-0.015 0.29 2.44 14
-0.015 0.29
Pentacene 0.1008 -0.037 2.12 1.93 18 11-35
b
0.084 6.06 10.90 3
0.055 3.14
DNTT 0.1272 -0.073 5.41 1.90 19 8.3c
0.089 5.05 2.83 12
0.012 0.11
C10-DNTT 0.1426 0.076 4.44 0.87 41 10d
-0.055 1.52 1.50 23
-0.055 1.52
C8-BTBT 0.2466 0.048 0.50 1.31 27 16.4e
0.022 0.07 1.66 21
0.022 0.07

Wide-band limit (NEGF): fast transmission calculations
for single-molecule junctions
Thesis Christopher Verzijl,
Thijssen group (Delft)
DFT-Based Molecular Transport
Implementation in ADF/BAND. J. Phys.
Chem. C, 116, 24393-24412 (2012).
e-

NEGF in BAND
Nature Nanotechnology 8, 282–287 (2013) Calc.: Verzijl, Thijssen group (Delft)
BAND calculations explain break-
through experiment on mechanical
and electrostatic effects in
molecular charge transport.
Image charges shift orbital
levels => dominate through-
molecule transport

NEGF in DFTB
Heine group (Jacobs U Bremen) Adv. Mater. 2013, 25, 5473–5475
Rippling in MoS2 strongly reduces conductance
Performance of these
materials may strongly
depend on production
methods.

NEGF in DFTB
Heine group (Jacobs U Bremen) SCIENTIFIC REPORTS | 3 : 2961 (2013)
Conductance in SWNT vs MWNT

Singlet Fission Yields in Organic Crystals:
N. Renaud, P. A. Sherratt, and M. A. Ratner, Mapping the Relation between Stacking Geometries
and Singlet Fission Yield in a Class of Organic Crystals, J. Phys. Chem. Lett., 4, 1065-1069 (2013)
Direct pathway dominates SF,
depends on crystal packing

Mechanism of DSSCs N3: Most typical dye
Three steps – all treated with ADF：
1. Photoexcitation of dye
2. Electron injection from dye to TiO2
3. Dye regeneration

Spin-orbit coupling increases dye efficiency
SOC-TDDFT: Incident photon to current efficiency (IPCE) of Ru sensitizer DX1
increased due to spectral broadening because of SOC
S. Fantacci, E. Ronca, and F. de Angelis, Impact of Spin–Orbit Coupling on Photocurrent
Generation in Ruthenium Dye-Sensitized Solar Cells, J. Phys. Chem. Lett., 5, 375-380 (2014)

Spin-orbit coupling increases dye efficiency
SOC indispensible to describe low-energy absorption bands of Os dyes
E. Ronca, F. de Angelis, and S. Fantacci, TDDFT Modeling of Spin-Orbit Coupling in Ru and Os
Solar Cell Sensitizers, J. Phys. Chem. C, just accepted
[Os(dcbpy)2(SCN)2]4-
exp
SR-TDDFT
SOC-TDDFT

Molecular design of Ru-dyes
• Ligands with extended p systems
⇒ red shift + increased absorption
F. Gajardo et al., Inorg. Chem. 50, 5910 (2011)

Electron injection from Ru dye to TiO2
F. Gajardo et al., Inorg. Chem. 50, 5910 (2011)
• Ruthenium polypiridyl dyes with extended π system
shows an enhancement of its light harvesting capacity.
• However, it is not necessarily reflected by an increase of
its efficiency as dye because an efficient electron
injection from the dye to TiO2 does not always occur.
Absorbed energy Delivered energy
[Energy flow on a typical dye sensitized solar cell]

Energy adsorbed ≠ Energy to TiO2
F. Gajardo et al., Inorg. Chem.
50, 5910 (2011)
Singlet
Triplet

Rational design of DSSC dyes
J. Phys. Chem. A 117, 430−438 (2013)
HOMO vs Hamett LUMO vs Hamett

Rational design of dyes for p-type DSSC
Light-harvesting efficiency = 1 - 10-f
Charge-separation efficiency =>
increase hole-e- separation
Hole-injection efficiency, Koopman’s
approximation:
DERP = EHOMO(dye) - E(VB)(electrode)
J. Wang et al. J. Phys. Chem. C
117, 2245−2251 (2013)

Rational design of dyes for p-type DSSC
J. Phys. Chem. C 117, 2245−2251 (2013)
Large separation
e- - electrode
Alkyne-spaced-ligands (4,6) also have high f =>
high Light Harvesting Efficiency
Hole-injection efficiency large for all ligands

J. Am. Chem. Soc., 136, 2876−2884 (2014)
Charge generation in fullerene-based OPVs
Charge generation facilitated by resonant coupling of singlet
excitons in polymer donors to fullerene electronic states
Diagonal couplings
Off-diagonal couplings
(transfer integrals)

E(V)
Scientific Reports, 4: 4033 (2014)
New, Robust Organic Dye: 10% conversion
TiO2 / dye / I-/I3
- redox couple
• spatially separated HOMO/LUMO:
facilitate e- injection & dye regeneration
• good alignment with TiO2 bands

Electron injection: Newns-Anderson
• Lorentzian distribution
• Center of the LUMO (ads) distribution
• Width of the broadening
 
i
ii Ep )ads(LUMO

i
iipE )ads(LUMO
 
2
2
LUMO
LUMO
2
)ads(
21
)(





 






 



EE
E
p

 
i
ii Ep )ads(LUMO
)meV(/658)fs(  
Electron injections time is
obtained from lifetime broadening
through:
Fitting of Lorentzian
distribution to adsorbate
LUMO PDOS ),( ii p
[J. Phys. Chem. B 2006, 110, 20513]

BINA on TiO2: injection times (Newns-Anderson)
• 2D system • PDOS analysis
BINA’s LUMO
The calculated electron injection time based on the Newns-Anderson approach
is 4.8 fs, below the exp. upper bound 7 fs [J. Phys. Chem. B 2004, 108, 3114].
Adsorbate PDOS
Total DOS

• Spin-Orbit Coupling, dispersion
• COSMO solvation crucial
• Formation N3-I2
- slowest step
N3 dye regeneration is rate-limiting step in DSSCs
A. M. Asaduzzaman and G. Schreckenbach,
Interactions of the N3 dye with the iodide redox shuttle:
quantum chemical mechanistic studies of the dye
regeneration in the dye-sensitized solar cell. Physical
Chemistry Chemical Physics, 13, 15148 (2011)

Modeling organic electronics with ADF

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