First Principles Computational Modelling of Solid/Liquid Interfaces for Solar Energy and Solar Fuels

First Principles Computational Modelling of Solid/Liquid Interfaces for Solar Energy and Solar Fuels Mariachiara Pastore Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO) Istituto CNR di Scienze e Tecnologie Molecolari, I-06123 Perugia, Italy Workshop IUPAC Italia Rome, 8th April 2014

Dye-Sensitized Solar Cells Introduction Solar Photocatalytic Cells

Multiscale modelling for higher efficiencies Modeling Dye dye the molecule/semiconductor and dye-semiconductor interactions interface are of paramount importance in determining the overall device conversion efficiency. Dye/catalyst anchoring: photocurrent, photovoltage and device stability Dye/catalyst co-adsorption and aggregation: energy, electron/hole transfer, excited state quenching Dynamical aspects Explicit interaction with solvents and other cell components: photovoltage, electronic coupling, aggregation Pastore, M.; De Angelis, F. J. Phys. Chem. Lett. 2013, 4, 956

Optical/redox properties of standalone chromophores Methods, models, tools Semiconductor cluster models Ru-complexes Fully organic (TiO 2 ) 38 (TiO 2 ) 82 Bipyramidal nancorystal (TiO 2 ) 367 Dye/catalyst/semiconductor interfaces Dye anchoring geometries (DFT, GGA) Electronic structure (DFT/implicit solvation models) CPMD simulations Absorption spectra and electronic properties (Hybrid TDDFT) squaraine in explicit water (90 molecules)

Modelling single dye adsorption on the TiO 2 surface

Adsorption modes on TiO 2 (Newns-Anderson ) the LUMO broadening (lorentzian) of the TiO 2 - adsorbed dye gives the electronic coupling Monodentate Bidentate The anchoring mode and the extent of electronic coupling directly influence the cell performances: CB energy shift (V oc ), electron injection and back recombination CB shift: 40% dye s electrostatic potential, 60% ground state charge transfer Pastore, M.; De Angelis, F.,Phys. Chem. Chem. Phys., 2012, 14, 920 Ronca, E.; Pastore, M.; Belpassi, L.; Tarantelli, F.; De Angelis, F. Energy Environ. Sci. 2013, 6, 183

Modelling multiple dye adsorption on the TiO 2 surface: aggregation

Dye Aggregation on TiO 2 : indoline dyes Dye-aggregation on the semiconductor surface is undesired (lower IPCE values) One rhodanin ring: strong aggregation Two rhodanin rings: weak aggregation 6-7% Uchida et al. Chem. Commun. 2003 - J. Am. Chem. Soc. 2004 Our strategy 8-9% Selecting dimeric arrangements on a (TiO 2 ) 82 slab Optimizations of selected structures Evaluating the relative stability of the optimized dimers Optical response simulation for the preferred arrangments M. Pastore, F. De Angelis ACS Nano, 2010, 4, 556.

Structures Selection and Optical Rensponse D149 D102 Dimer D102 D149 (0,2) 0.0 4.5 (2,2) 3.9 0.0 MP2 relative stability (kcal/mol) Monomer Dimer Dye Exc. f Exc. Shift Exp. D102 2.11 0.82 1.96 0.15 0.22 D149 2.06 0.80 1.97 0.08 0.06 *TDDFT(B3LYP)/6-31G* excitation energies in EtOH M. Pastore, F. De Angelis ACS Nano, 2010, 4, 556.

Co-adsorption on TiO 2 : Modeling different dyes adsorption and FRET

Exploiting FRET in DSCs Enhancing the light harvesting in the red by cosensitization of TiO 2 surface with organic dyes having high NIR absorption FRET hν Rate of FRET k F = 1 6 R 0 τ 0 r A r D 6 Where the Foster radius is given by R 6 0 = 9000 ln(10)κ2 Q D 128π 5 n 4 N A F D (λ)ε A (λ)λ 4 dλ e - SD (C106) NIR- ERD (AS02) Hardin, B. E.; Sellinger, A.; Moehl, T.; Humphry-Baker, R.; Moser, J.-E.; Wang, P.; Zakeeruddin, S. M.; Grätzel, M.; McGehee, M. D., J. Am. Chem Soc. 2011, 133, 10662.

Modeling FRET Förster type intramolecular energy transfer mediated by resonant dipoles Rate of FRET Orientation factor Spectral overlap k F = 1 6 R 0 Where the Foster 6 R τ 0 0 r A r D radius is given by 6 = 9000 ln(10)κ 2 Q D 128π 5 n 4 N A F D (λ)ε A (λ)λ 4 dλ with N A being the Avogadro s number and n the refractive index of the medium. The dimensionless orientation factor κ 2 can vary from 0 to 4 and is given by κ 2 = (cosγ 3cosα cosβ ) 2 For randomly oriented donoracceptor dipole moments, κ 2 is equal to 2/3

Aggregates and FRET Modeling Strategy Anchoring geometries onto the (TiO 2 ) 82 slab Selecting the closest interacting ones (Ti active sites grid) +1.6 0.0 Stability analysis Geometrical orientation factor κ 2 calculation +15.6 Possible co-adsorption schemes of AS02 sorrounded by four C106 molecules and relative energies in kcal/mol. Pastore, M.; De Angelis, F., J. Phys. Chem. Lett., 2011, 3, 2146 2153

Calculated Κ 2, Föster Radii and FRET rates Pastore, M.; De Angelis, F., J. Phys. Chem. Lett., 2011, 3, 2146 2153

Modelling the complex cell environment

Dye-Iodine-TiO 2 Interactions Organic dyes with common I - /I 3 - electrolyte generally show lower V oc compared to Ru-based dyes lower electron lifetimes 11 Å 17 Å -1.9 kcal/mol Oxygen atoms are the preferred binding sites for I 2-4.3 kcal/mol -2.1 kcal/mol Pastore, M.; Mosconi, E; De Angelis, F. J. Phys. Chem. C 2012, 116, 5965 Planells, M.; Pelleja, L.; Clifford, J. N.; Pastore, M.; De Angelis, F.; Lopez, N.; -2.5 Marder, S. R.; Palomares, E. Energy kcal/mol Pastore, M.; Mosconi, E; De Angelis, F. J. Phys. Environ. Chem. Sci. C 2011, 2012, 4, 116, 1820 5965

Dye-ionic additives-tio 2 Interactions Addition of Lithium salts improves the measured photocurrents Li + Calculated CB shift Li + d k inj = 2π h Nacc k=1 V dk 2 ρ(εk ) LUMO/CB states coupling Li + Molecular packing amplifies the effect! Injection rate distribution Li + Agrawal, S.; Leijtens, T.; Ronca, E., Pastore, M.; Snaith, H.; De Angelis, F. J. Mater. Chem. A, 2013, 1, 14675-14685

Effect of TiO 2 protonation on the charge generation Surface protonation is usually employed for improving J sc CB donwnshift? red-shifted dye absorption? -0.1 ev per H + Ronca, E.; Marotta, G.; Pastore, M.; De Angelis, F. J. Phys. Chem. C 2014, In Press. DOI: 10.1021/jp5004853

Effect of TiO 2 protonation on the charge generation Acidic treatment NO Jsc (ma/cm 2 ) Voc (V) FF Eff. (%) 5.780 0.734 0.688 2.92 Red-shifted absorption YES 7.500 0.713 0.699 3.74 Max. J sc gain for the the spectral red-shift is about 0.7 ma/cm 2! 1H + 5H + d k inj = 2π h Nacc k=1 V dk 2 ρ(εk ) Increased electronic coupling improved charge generation

Dye-Sensitized Photocatalytic Cells

Forthcoming research activity: Short term goals Stable anchoring on the SC in water and oxidative environment Optimal dye/catalyst ratio on the surface Optimal geometrical arrangement of the dye/catalyst assembly Maximizing the forward energy and electron transfer processes Minimizing excited state quenching and back recombination reactions Screening of novel anchoring groups stable in oxidative and water environments Simulating molecular/catalyst aggregates in model architectures and operative experimental conditions (full coverage) through QM/MM and MD simulations Energy Environ. Sci. 2011, 4, 2389 J. Am. Chem Soc. 2013, 135, 4219

Modelling dye/catalyst/tio 2 for water splitting (IrO 2 ) 56 2H 2 O W. J. Youngblood, S.-H. A. Lee, Y. Kobayashi, E. A. Hernandez-Pagan, P. G. Hoertz, T. A. Moore, A. L. Moore, D. Gust, and T. E. Mallouk J. Am. Chem. Soc. 131, 2009, 926-927 (TiO 2 ) 82 Stability of the dye/catalys assemby on the TiO 2 Energy levels alignment Electronic coupling for injection and regeneration

CLHYO Perugia Dr. Filippo De Angelis Enrico Ronca Gabriele Marotta Thanks to Oxford University Prof. H. Snaith Financial support: FP7-NMP-2009 SANS - FP7-ENERGY-2010 ESCORT FP7-ICT-2011 SUNFLOWER CNR EFOR 2011 IIT-SEED 2009 and you for your kind attention