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2) Charge mobility (e.g. OFETs) 3) PVs/DSSC: singlet fission, excitation, e- injection, regeneration published papers & unpublished calcs by Mr.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 Copyright © 2014, SCM. Phosphors in OLEDs - A + C + from Hartmut Yersin Copyright © 2014, SCM. h-e recombination: 25% S, 75% T excitons: Need to harvest Triplets: TM with large SOC 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. 2014, in print Copyright © 2014, SCM. 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) Copyright © 2014, SCM. Designing ligands for better phosphors in OLEDs with pSOC-TDDFT A. R. G. Smith, M. J. Riley, P. L. Burn, I. R. Gentle, S.-C. Lo, and B. J. Powell Effects of Fluorination on Iridium(III) Complex Phosphorescence: Magnetic Circular Dichroism and Relativistic TDDFT Inorg. Chem., 51, 2821-2831 (2012). Copyright © 2014, SCM. Vibronic fine structure OLED phosphor Pt complex: vibrational progression from T1 → S0 emission Courtesy of Mr. Kento Mori, Ryoka, unpublished results unpublished calcs byCopyright Mr. Mori, Ryoka Inc. on TSUBAME2.0, JACI © 2014, SCM. Methods to calculate charge mobilities • Hopping transport: – Charge transfer integrals + other elements, directly printed – Electronic couplings from frozen-density embedding h+ • 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) Copyright © 2014, SCM. Q Hole / electron mobilities • • Ordered crystals (low T) => band-like transport µ αβ = eτ (m −1 )αβ 1 ∂ 2ε (k ) =− 2 ∂kα ∂k β (m ) −1 αβ Amorphous materials: incoherent hopping Pi = ki ∑ ki i • Accoustic deformation potential 3 µ= e BLeff ε ac2 (k BT )(mc md ) mc: the effective mass along the direction of transport md: the density of states mass, (ma mb)1/2 εac: the acoustic deformation potential, V dEvbm/dV B: the elastic modulus Leff: the length of the π-bonded core of the molecule Copyright © 2014, SCM. Effective transfer integral Jeff = electronic coupling V • Definition of fragments • Matrix elements from ADF (a) “transfer integral” C1 C2 J RP = ϕ HOMO hks ϕ HOMO (b) spatial overlap C1 C2 S RP = ϕ HOMO ϕ HOMO Molecular crystal of pentacene (c) site energy extract dimer C1 C1 H RR = ϕ HOMO hks ϕ HOMO C2 C2 H PP = ϕ HOMO hks ϕ HOMO Fragment C1 Fragment C2 J RP − S RP (H RR + H PP ) / 2 V= 2 1 − S RP orthogonalization Copyright © 2014, SCM. Anisotropic hole mobilities in pentacene Anisotropic mobility： S.-H. Wen et al., J. Phys. Chem. B 113, 8813 (2009) Copyright © 2014, SCM. Oligofuran vs Oligothiophene 6F: µ 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) Copyright © 2014, SCM. Hole transport in tetrathienoarenes Y.-A. Duan et al., Organic Electronics 15, 602-613 (2014) Copyright © 2014, SCM. Transport in N-hetero-pentacenes X.-K. Chen et al., Organic Electronics 13, 2832-2842 (2012) Copyright © 2014, SCM. Transport in ladder-type molecules H.-L. Wei, Y.-F. Liu, Appl. Phys. A, in press(2014) Copyright © 2014, SCM. Environment effects: frozen-density embedding Scales linearly with number of molecules included in environment Effect on couplings and excitation energy larger for more polar systems 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 N C2H4 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). Copyright © 2014, SCM. Environment effects: transport in 1D wires hybrid quantum-classical model with polarizable force field including dynamic and static disorder A. A. Kocherzhenko et al., Effects of the Environment on Charge Transport in Molecular Wires, J. Phys. Chem. C. 116 25213-25225 (2012). Copyright © 2014, SCM. Band Transport • Drude model [J. Phys. Chem. C 114, 10592 (2010)] µ αβ = eτ (m −1 )αβ • τ: the mean relaxation time of the band state m: the effective mass of the charge carrier, (m ) −1 αβ 1 ∂ 2ε (k ) =− 2 ∂kα ∂k β Acoustic deformation potential model [Appl. Phys. Lett. 99, 062111 (2011)] µ= e 3 BLeff ε ac2 (k BT )(mc md ) mc: the effective mass along the direction of transport md: the density of states mass, (ma mb)1/2 εac: the acoustic deformation potential, V dEvbm/dV B: the elastic modulus Leff: the length of the π-bonded core of the molecule Copyright © 2014, SCM. hopping transport (P, T1, T2) Rubrene Pentacene DNTT C10-DNTT C8-BTBT band transport (a, b) experiment λ (eV) V (eV) µ (cm2V-1s-1) m/m0 µ (cm2V-1s-1) µ (cm2V-1s-1) 0.1460 -0.082 7.22 0.99 36 20-40a -0.015 0.29 2.44 14 -0.015 0.29 -0.037 2.12 1.93 18 0.084 6.06 10.90 3 0.055 3.14 -0.073 5.41 1.90 19 0.089 5.05 2.83 12 0.012 0.11 0.076 4.44 0.87 41 -0.055 1.52 1.50 23 -0.055 1.52 0.048 0.50 1.31 27 0.022 0.07 1.66 21 0.022 0.07 0.1008 0.1272 0.1426 0.2466 b 11-35 unpublished calcs byCopyright Mr. Mori, Ryoka Inc. on TSUBAME2.0, JACI © 2014, SCM. 8.3c 10d 16.4e Wide-band limit (NEGF): fast transmission calculations for single-molecule junctions e- Thesis Christopher Verzijl, Thijssen group (Delft) DFT-Based Molecular Transport Implementation in ADF/BAND. J. Phys. Chem. C, 116, 24393-24412 (2012). Copyright © 2014, SCM. NEGF in BAND Image charges shift orbital levels => dominate throughmolecule transport BAND calculations explain breakthrough experiment on mechanical and electrostatic effects in molecular charge transport. Nature Nanotechnology 8, 282–287 (2013) Calc.: Verzijl, Thijssen group (Delft) Copyright © 2014, SCM. NEGF in DFTB Rippling in MoS2 strongly reduces conductance Performance of these materials may strongly depend on production methods. Heine group (Jacobs U Bremen) Adv. Mater. 2013, 25, 5473–5475 Copyright © 2014, SCM. NEGF in DFTB Conductance in SWNT vs MWNT Heine group (Jacobs U Bremen) SCIENTIFIC REPORTS | 3 : 2961 (2013) Copyright © 2014, SCM. Singlet Fission Yields in Organic Crystals: Direct pathway dominates SF, depends on crystal packing 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) Copyright © 2014, SCM. 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 Copyright © 2014, SCM. 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) Copyright © 2014, SCM. Spin-orbit coupling increases dye efficiency [Os(dcbpy)2(SCN)2]4exp SR-TDDFT SOC-TDDFT 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 Copyright © 2014, SCM. Molecular design of Ru-dyes • Ligands with extended π systems ⇒ red shift + increased absorption F. Gajardo et al., Inorg. Chem. 50, 5910 (2011) Copyright © 2014, SCM. Electron injection from Ru dye to TiO2 • 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. [Energy flow on a typical dye sensitized solar cell] Absorbed energy Delivered energy F. Gajardo et al., Inorg. Chem. 50, 5910 (2011) Copyright © 2014, SCM. Energy adsorbed ≠ Energy to TiO2 Singlet Triplet F. Gajardo et al., Inorg. Chem. 50, 5910 (2011) Copyright © 2014, SCM. Rational design of DSSC dyes LUMO vs Hamett HOMO vs Hamett J. Phys. Chem. A 117, 430−438 (2013) Copyright © 2014, SCM. 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: ∆ERP = EHOMO(dye) - E(VB)(electrode) J. Wang et al. J. Phys. Chem. C 117, 2245−2251 (2013) Copyright © 2014, SCM. Rational design of dyes for p-type DSSC 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. Phys. Chem. C 117, 2245−2251 (2013) Copyright © 2014, SCM. Charge generation in fullerene-based OPVs resonant coupling of singlet excitons to fullerene electronic states facilitates efficient charge generation in OPVs J. Am. Chem. Soc., 136, 2876−2884 (2014) Copyright © 2014, SCM. Electron injection: Newns-Anderson • Lorentzian distribution ρ LUMO ( E ) = Γ 2 1 π Fitting of Lorentzian distribution to adsorbate LUMO PDOS (ε i , pi ) (E − ELUMO (ads) )2 + Γ 2 2 • Center of the LUMO (ads) distribution ELUMO (ads) = ∑ piε i i Electron injections time is obtained from lifetime broadening through: τ (fs) = 658 / Γ (meV) • Width of the broadening Γ = ∑ pi ε i − ELUMO (ads) [J. Phys. Chem. B 2006, 110, 20513] i Copyright © 2014, SCM. BINA on TiO2: injection times (Newns-Anderson) • 2D system • PDOS analysis BINA’s LUMO Adsorbate PDOS Total DOS 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]. unpublished calcs byCopyright Mr. Mori, Ryoka Inc. on TSUBAME2.0, JACI © 2014, SCM. N3 dye regeneration is rate-limiting step in DSSCs • Spin-Orbit Coupling, dispersion • COSMO solvation crucial • Formation N3-I2- slowest step 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) Copyright © 2014, SCM.
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