FINNISH-JAPANESE WORKSHOP ON FUNCTIONAL MATERIALS Espoo-Helsinki May, 2009

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1 FINNISH-JAPANESE WRKSHP N FUNCTINAL MATERIALS Espoo-Helsinki May, 2009 THEMATIC WRKING GRUP: MATERIALS FR NEW ENERGY SLUTINS, SLAR CELL & BATTERY Fast spectroscopy Synthesis of functional molecules Function in supramolecular structures Prof. Helge Lemmetyinen Laboratory of Chemistry Tampere University of Technology, FINLAND

2 From Kinetics to Dynamics Svante Arrhenius (1889): or k = A exp (-E a /RT) ln k = -E a /RT + C We need to know: how reagent molecules approach, collide, exchange energy, break bonds and make new ones, and finally separate into products

3 From Kinetics to Dynamics Henry Eyring and Michael Polanyi (1931): Potential energy surphase Eyring, Polanyi and Evans (1935): Transition-state theory k = (kt/h) (Q /Q A Q B ) exp (-E o /kt) The fastest reaction at room temperature: k = (kt/h) 6 x s -1 or = 170 fs The time scale of molecular vibrations is typically fs

4 Femtochemistry Nobel Laureate in Chemistry 1999 Ahmed H. Zewail

5 Ultra-fast Spectroscopy at TUT: Photo-induced Electron Transfer reaction Pheophytin-fullerene derivative: fluorescence spectra and lifetimes J. Am. Chem. Soc., 121, 1999, 3978 Lemmetyinen, Tkachenko et al.. Reference Pheopytin: 1 = 4 5 ns toluene benzonitrile PaF: 1 = 0.59 ps 0.54 ps 2 = 8.5 ps 4.4 ps

6 Pheophytin-fullerene derivatives: Time-resolved component spectra: in non-polar toluene three components in polar benzonitrile four components J. Am. Chem. Soc., 121, 1999, 3978 Lemmetyinen, Tkachenko et al. D*A k en A*D k px (DA)* k xc D + s A - k csg DA 0.35 ps = k en energy transfer 8 ps = k px exciplex formation 19 ps = k xcs CT-state formation 65 ps = k csg CT-state recombination

7 Porphyrin-fullerene series: covalently linked with two chains k px k fx k xp k xf k xcs TBD4be DHD6ee k csg k px = x s -1 e.g TBD6be ZnD7mee k xcs = x s -1 e.g k csg = x 10 9 s -1 e.g J. Phys. Chem., B, 108, 2004, Lemmetyinen, Tkachenko, Guldi et al.

8 Joint publications on Electron-Transfer and Solar Cells with Groups of Prof. Fukuzumi (saka) and Imahori (Kyoto) N.V. Tkachenko, C. Guenther, H. Imahori, K. Tamaki, Y. Sakata, S. Fukuzumi, and H. Lemmetyinen: Near infra-red emission of charge-transfer complexes of porphyrinfullerene films, Chem. Phys. Lett., 326, 2000, Hiroshi Imahori, Nikolai V. Tkachenko, Visa Vehmanen, Koichi Tamaki, Helge Lemmetyinen, Yoshiteru Sakata, and Shunichi Fukuzumi: An Extremely Small Reorganization Energy of Electron Transfer in Porphyrin-Fullere Dyad, J. Phys. Chem. A, 105, 2001, Visa Vehmanen, Nikolai V. Tkachenko, Hiroshi Imahori, Shunichi Fukuzumi, and Helge Lemmetyinen: Charge-transfer emission of compact porphyrin-fullere dyad analyzed by Marcus theory of electron-transfer, Spectrochimic. Acta, A 57, 2001, Tero J. Kesti, Nikolai V. Tkachenko, Visa Vehmanen, Hiroko Yamada, Hiroshi Imahori, Shunichi Fukuzumi, and Helge Lemmetyinen: Exciplex intermediates in photoinduced electron transfer of porphyrin-fullerene dyads, J. Am. Chem. Soc., 124, 2002,

9 Joint publications on Electron-Transfer and Solar Cells with Groups of Prof. Fukuzumi (saka) and Imahori (Kyoto) Chem. Phys. Lett., 366, 2002, Photochem. Photobiol. Sci., 2, 2003, J. Phys. Chem., 107, 2003, J. Phys. Chem., 107, 2003, J. Am. Chem. Soc.,126, 2004, Langmuir, 21, 2005, J. Phys. Chem., B 109, 2005, Chem. Eur. J., 11, 2005, J. Phys. Chem., B 109, 2005, J. Mater. Chem., 15, 2005, J. Phys. Chem., A, 109, 2005, Langmuir, 21, 2005, Langmuir, 22, 2006, Chem. Phys., 326, 2006, 3-14 rg. Lett., 8, 2006, J. Phys. Chem. C, 111, 2007, J. Phys. Chem. C, 111, 2007, Chem. Eur. J. 13, 2007, Langmuir 23, 2007, J. Phys. Chem. C, 112 (26), 2008, J. Phys. Chem., A, 112, 2008, J. Phys. Chem. B, 112, 2008, Chem. Asian. J., 3, 2008, J. Phys. Chem. C, 113, 2009, 1984-

10 Marcus electron transfer theory

11 Marcus electron transfer theory and more complex multistep reactions The Marcus theory works well for the one step ET and BET. However, more complex reactions, with one or more intermediate steps, may be difficult to interpret quantitatively with the 1-dimensional model.

12 A series of electron donor-acceptor compounds were studied

13 Three-dimensional surfaces for the ET reaction: free energy, distance and solvent polarization a) Mixing of states D*A and D + A - is not taken into account b) Mixing of states is taken into account D*A D + A - J. Phys. Chem. A, 111, 2007, 9240 Murata & Tachiya

14 A topographic surface for the ET reaction: free energy, distance and solvent polarization: As r decreases exciplex formation occurs, mainly in non-polar solvent, but can be stabilized by solvation No (or small) activation energy is needed for exciplex and ion formation! N TEMPERATURE DEPENDENCE!? J. Phys. Chem. A, 111, 2007, 9240 Murata & Tachiya

15 Studies of temperature dependent ultrafast photoinduced charge transfer in donor-acceptor pairs forming exciplexes All the compounds, except P-BQ form exciplex as a Will be published in Hiroshi Masuhara Festschrift, J. Phys. Chem. C., June 2009 transient state

16 Left: a) Formation of exciplex and b) decay of the CT state of TBD6e in THF at different temperatures. Right: The component spectra and their lifetimes of transient states of TBD6e in THF at temperatures of a) 305 K and b) 205 K.

17 a) The component spectra and their lifetimes of transient states of P-BQ in toluene at temperature of 190 K and b) decays of the CT state of P-BQ at different temperatures.

18 Comparison of micro-and pico-second time-scales for a doublebridged porphyrin-fullerene dyad in solid film DHD6ee TBD Superposition of radical cation of porphyrin and radical anion of fullerene in ps and s time-scales Pc * - C 60 Pc + -C 60 - Pc + -C 60 -

19 Molecules in self-assembled or organized phase: in 2D films vectorial electron transfer takes place and Electrode e - PHT = a conductive polymer h e - Electrode

20 ... and thus create photovoltage or photocurrent? Electrode e - V h e - e - Electrode

21 Vectorial electron transfer in solid films was measured by applying a Maxwell displacement charge measurement technique (Transient Photovoltage) Glass IT electrode DA layers Active layers DA layers Al electrode hv U bias R in U out (t)

22 rientation of molecular thin films were obtained by using the Langmuir-Blodgett technique: The LB-film structures for photovoltage measurements DHD6ee IT IT 11 DA e - e - 20 DA Al-electrode DHD6ee PHT DA

23 Intensity of the photovoltage signals depends on number of electrons moving and on the distance of the movement Al e - IT (a lower excitation intensity was used)

24 Molecular Engineering: Building a Device: The elements for preparing of supramolecular film structures IT = PHT = PHT PVT3 = PVT3 PPQ = PPQ

25 Sensitivity hotovoltage signals for PVT3/Dyad/PPQ film systems amplitude time, ns PPQ - PVT3 acts as an energy donor to the porphyrin moiety - PPQ acts as electron acceptor from fullerene anion radical - PHT acts as an electron donor to porphyrin cation radical PPQ = PVT3 PVT3 PVT3 PHT Lifetimes are in time scale of tens of seconds!

26 Sensitivity of the photovoltage signals PHT/P-F/PTCDI film systems PhC 2 H 4 H N N M N N P-F H HN PTCDI PHT NH * S n *

27 rganic solar cell configurations LAYERED _ + BULK HETERJUNCTIN _ + Al or Au Al or Au IT PLASTIC or GLASS IT PLASTIC or GLASS Electron donor (HTL) Electron acceptor (ETL)

28 I-V characteristics of multilayered cells containing H 2 PcC 60 ee I, ma cm I, ma cm dark illuminated U, V Top electrode PTCDI H 2 PcC 60 ee PHT IT HN N N NH N N N HN N A B illuminated U, V NH dark Top electrode C 60 H 2 PcC 60 ee PHT IT C D

29 Photovoltaic parameters Structure I sc, ma/cm 2 U oc, V FF η, % IPCE, % PHT PTCDI Alq PHT H 2 PcC 60 ee PTCDI Alq PHT C 60 Alq PHT H 2 PcC 60 ee C 60 Alq

30 Normalized IPCE Abs Normalized IPCE Abs Action and absorption spectra: comparison wavelength, nm Top electrode PTCDI H 2 PcC 60 ee PHT IT ref. IPCE A Abs A dyad IPCE B Abs B Top electrode C 60 H 2 PcC 60 ee PHT IT ref. 0.4 IPCE C Abs C 0.3 IPCE D dyad Abs D wavelength, nm

31 Monochromatic light: quantum yields Structure l, nm I sc, Abs. F EXT, ma/cm 2 % F INT, % PHT PTCDI Alq PHT H 2 PcC 60 ee PTCDI Alq PHT:H 2 PcC 60 ee PTCDI Alq

32 Mixing of PHT and H 2 PcC 60 ee Top electrode PTCDI H 2 PcC 60 ee PHT IT Top electrode PTCDI PHT:H 2 PcC 60 ee IT Structure I sc, ma/cm 2 U oc, V FF η, % IPCE, % PHT:H 2 PcC 60 ee PTCDI Alq

33 Acknowledgements 33 Prof. Nikolai Tkachenko Dr Elina Vuorimaa Dr Alexander Efimov Dr Vladimir Chukharev Dr Riikka Lahtinen Dr Marja Niemi Dr Kimmo Kaunisto MSc Anne Kotiaho MSc Heli Lehtivuori MSc Paolo Vivo MSc Kalle Lintinen MSc Antti Tolkki Tampere University of Technology, Finland National Technology Agency Tekes Nanochemistry and rganic Solar Cell Academy of Finland Graduate School of Molecular Nanotechnology (99-02) The Finnish National Graduate School in Nanoscience