THREE: Organic OptOelectronics
We have further extended the range of high performance alternating phenylene/donor-acceptor-donor polymers for solar cell blends, giving us some of the best device efficiencies.
Photophysical processes in materials:
Extensive time resolved spectroscopy study on alternating polyfluorene copolymer/fullerene(C60 PCBM) blends of varying composition, including the neat polymer, covering ten decades of time and three orders of magnitude of excitation light intensity, in combination with sophisticated kinetic modelling, established a comprehensive model of energy transfer, excited state dynamics, charge photogeneration and recombination. It was shown that at solar cell operational conditions first-order charge recombination may be a limiting factor for obtaining high photon-to-charge quantum efficiencies. The work suggested that modification of charge carrier mobility and material morphology could be ways to improve material performance. Very efficient charge formation already at very low (< 10%) C60-PCBM concentrations show that charge generation is not a limiting factor for efficient solar cell performance.
Charge photogeneration in polymer/C70-PCBM blends of varying composition has been studied in a similar way as for polymer/C60-PCBM above. It was found that charge recombination is substantially slower in the polymer/C70-PCBM blends than in the corresponding C60-PCBM blends, supporting the view that charge recombination may limit the performance of organic bulk heterojunction solar cells.
Time-resolved terahertz spectroscopy was used for investigation of photo-induced charge carrier dynamics in blends of a polyfluorene copolymer /C60-PCBM as above. The transient far-infrared response appears instantaneously after photoexcitation. We show that the transient conductivity spectrum is dominated by two major contributions: response of separated charge carriers, and response of coupled polaron pairs. Time-resolved terahertz spectroscopy was also used to investigate photoinduced dynamics of charge carriers in a blend of a low-band-gap polyphenylene copolymer and electron acceptor. We reveal a nearly instantaneous generation of highly mobile holes delocalized within states on polymer chains. This highly non-equilibrium state evolves towards a quasi-equilibrium trapped-controlled transport regime. We resolve the initial part of this process, which appears as a drop of mobility by two orders of magnitude on a sub-picosecond time scale.
Interfaces in organic devices:
The Integer Charge Transfer model for energy level alignment at weakly-interacting organic-metal and organic-organic interfaces have been tested for molecules, previously having been confirmed for polymers. Earlier results obtained in the project for Alq3 and C60 suggested that the model holds for so-called small molecules as well and this was indeed confirmed, as was the existence of integer charged states at the organic-metal interface as an effect of spontaneous charge transfer across the interface. The self organization of APFO-9/PCBM blends at the (buried) anode contact in bulk heterojunction solar cells has been studied, showing that the anode interface is primarily PCBM/ITO and PCBM/PEDOT-PSS, i.e., the acceptor material is preferentially segregating to the anode for both ITO and PEDOT-PSS.
We have completed three strategies towards enhanced light incoupling in plastic solar cells, using light trapping in folded and tandem solar cells, selfaligned microlenses and plasmon enhancers. The most successful solution, folded cells, almost doubles power conversion efficiency. Electromagnetic modelling of optical incoupling completed, indicating limits to the effect due to electrode absorption.
We have developed a method to study the impact of torsional dynamics on the charge carrier mobility in conjugated polymers. Transport in field effect transistors and in electrolyte gated transistors has been studied using a method based on Marcus theory of electron transfer. Dipole layers at the interface between metallic (Au) gold contacts and organic can be used to considerably change barriers for injection.
Using the Green function technique previously developed we studied the effect of surface plasmons on the enhancement of the absorption in polymeric solar cells. The good match between the measured and the simulated reflectances demonstrates the strong influence of the surface plasmons on absorption in the structure.
We have applied three-dimensional (3D) finite-difference time-domain method (FDTD) to study the excitation of surface plasmons in two different structures: (a) on a flat metallic surface by coupling of the plasmonic evanescent waves in spherical nanoparticles and plasmons on a metal surface and (b) on a two-dimensional metal grating. We have demonstrated that surface plasmons can be excited on a plane metal surface by the evanescent waves of plasmons induced in nanoparticles according to the scheme: propagating waves-->particle plasmons-->evanescent waves-->surface plasmon. Using silver surface and nanoparticles we have visualized the excited plasmon and estimated its propagation length, which was ~ 1 m m. We have also shown the process of a plasmon excitation on a 2D grating and suggested employing the grating for enhancement of absorptance in electrochromic devices.
Publikationer, patent, nyttiggörande, mm under de senaste 12 månaderna
· L. Herlogsson, X. Crispin, N. D. Robinson, M. Sandberg, O.-J. Hagel, G Gustafsson, M. Berggren, ”Low-voltage polymer field-effect transistors gated via a proton conductor”, Advanced Materials vol. 19 no. 1, pp. 97-101 (2007)
· M. Berggren, D. Nilsson, N. D. Robinson, “Organic materials for printed electronics”, Nature Materials vol. 6, pp. 3-5 (2007)
· P. Tehrani, A. Kanciurzewska, X. Crispin, N. D. Robinson, M. Fahlman, M. Berggren, “The effect of the pH on the electrochemical over-oxidation in PEDOT:PSS films”, Solid State Ionics, 177, 3521-3527 (2007).
· F. L. E. Jakobsson, X. Crispin, M. Cölle, M. Büchel, D. M. de Leeuw, M. Berggren, On the switching mechanism in Rose Bengal-based memory devices, Organic Electronics, vol. 8, no. 5, pp. 559-565 (2007)
· P. Andersson, R. Forchheimer, P. Tehrani, and M. Berggren, Printable all-organic electrochromic active-matrix displays, Advanced Functional Materials, vol. 17, no. 16, pp. 3074-3082 (2007)
· Zhang, T.; Ceder, M.; Inganas, O., Enhancing the photovoltage of polymer solar cells by using a modified cathode. Advanced Materials 2007, 19, (14), 1835-+.
· Tvingstedt, K.; Persson, N. K.; Inganas, O.; Rahachou, A.; Zozoulenko, I. V., Surface plasmon increase absorption in polymer photovoltaic cells. Applied Physics Letters 2007, 91, (11), 113514.
· Tvingstedt, K.; Inganas, O., Electrode grids for ITO-free organic photovoltaic devices. Advanced Materials 2007, 19, (19), 2893-+.
· Tvingstedt, K.; Andersson, V.; Zhang, F.; Inganas, O., Folded reflective tandem polymer solar cell doubles efficiency. Applied Physics Letters 2007, 91, (12), 123514.
· Persson, N. K.; Wang, X. J.; Inganas, O., Optical limitations in thin-film low-band-gap polymer/fullerene bulk heterojunction devices. Applied Physics Letters 2007, 91, (8), 083503.
· Hamedi, M.; Forchheimer, R.; Inganas, O., Towards woven logic from organic electronic fibres. Nature Materials 2007, 6, (5), 357-362.
· A. Kanciurzewska, E. Dobruchowska, A. Baranzahi, E. Carlegrim, M. Fahlman and M.A. Girtu, J. Optoel, Study on Poly(3,4-ethylene dioxythiophene)-Poly(styrenesulfonate) as a plastic counter electrode in dye sensitized solar cells, Adv. Mat. 9 (2007) 1052.
· S. Braun, M. P. de Jong, W. Osikowicz and W. R. Salaneck, Influence of the electrode work function on the energy level alignment at organic-organic interfaces, Appl. Phys. Lett. 91 (2007) 202108.
· S. Braun and W. R. Salaneck, Fermi level pinning at interfaces with tetrafluorotetracyanoquinodimethane (F4-TCNQ): The role of integer charge transfer states., Chem. Phys. Lett. 438 (2007) 259.
· S. Braun, W. Osikowicz, Y. Wang and W. R. Salaneck, Energy level alignment regimes at hybrid organic-organic and inorganic-organic interfaces., Org. Electron. 8 (2007) 14.
· I. Rahachou and I. V. Zozoulenko, “ Light propagation in nanorod arrays”, J. Opt. A: Pure Appl. Opt. 9, 265 (2007).
· M. Hultell and S. Stafström, Impact of ring torsion on the intra-chain mobility in conjugated polymers, Phys. Rev. B, 75, 104304 (2007).
· L. Demeyu, M. Bekele, and S. Stafström, Gate controlled distribution of potassium ion in intercalated pentacene, phys. stat. sol. (a) 204(10) 3545-3555 (2007).
· L. Demeyu, M. Bekele, and S. Stafström, Monte Carlo simulations of charge transport in organic field-effect transistor devices, Phys. Rev. B, 76, 155202 (2007).
· V. Gulbinas, I. Mineviciute, D. Hertel, R Wellander, A. Yartsev V. Sundstrom. Exciton diffusion and relaxation in m-LPPP polymer films. J. Chem. Phys. 127 (2007) 144907
· V. Gulbinas, D. Hertel, A. Yartsev V. Sundstrom. Charge carrier generation and recombination in ladder-type poly (para-phenylene). Phys. Rev B.76 (2007) 10589-97
· M Westerling, H Aarnio, R Österbacka, H Stubb, SM King, AP Monkman, MR Anderson, K Jespersen, T Kesti, A Yartsev, V Sundström. Photoexcitation dynamics in an alternating polyfluorene copolymer. Phys Rev B75 (2007) Art n0 224306
· S De, T Kesti, T Pascher, MR Andersson, O Inganäs, A Yartsev, V Sundström. Geminate charge recombination in a low bandgap polyfluorene-fullerene solar cell material controls light-to-charge conversion quantum efficiency. J Am Chem Soc 129 (2007) 8466
· Ivan Scheblykin, Arkady Yartsev, Tonu Pullerits, Vidmantas Gulbinas, Villy Sundström. Excited state and charge photogeneration dynamics in conjugated polymers. J. Phys. Chem B.Feature article. 111 (2007) 6303-21
. Yuri Zaushitsyn, Kim G Jespersen, l. Valkunas, Villy Sundström and Arkady Yartsev.
Ultrafast dynamics of singlet-singlet and singlet-triplet exciton annihilation in conjugated polymers. Phys. Rev. B 75 (2007) 195201
1 . “Polymer thin-film transistor gated via an electric double layer”, by L. Herlogsson, G. Gustafsson, O.-J. Hagel, M. Sandberg, M. Berggren, X. Crispin, N. Robinson, EPO06123785.5-2203 and US patent pending.
2. SE0602612-4 + PCT/EPO
Mahiar Hamedi, Olle Inganäs, Maria Asplund, Robert Forchheimer: Elektroniska kretsar integrerade i tyg /Electronic circuitry integrated in fabrics
3 . SE/0602492-1 + PCT/ EPO
Kristofer Tvingstedt, Olle Inganäs:Multijunction photovoltaic cells and methods to produce them
4 . “Photovoltaic device with enhanced light harvesting”. Inventors: Massimo Tormen, Olle Inganas, Kristofer Tvingstedt, Simone Dal Zilio. PCT N. PCT/EP2007/055145 on the 28.05.2007 by CONSIGLIO NAZIONALE DELLE RICERCHE- INFM.
Activities in COE are funded until March 31, 2008, and we have extended the period in some groups. A final COE report is due 2009. Two PIs (SS, OI) have been invited to give Keynote talks at the International Conference on Synthetic Metals in Brazil, 2008, the major meeting on electronic organic solids.
Two companies have been formed or are under formation from COE activities, PaperDisplay from Acreo activities and Soleve AB, from polymer solar cells.
The COE director, Olle Inganäs, has been on sick leave most of November 2007- March 2008.
Eventuella styrgruppsmöten under året, datum
February 14, Linköping, August 29 2007, at the end of the COE summery meeting outside Norrköping
Antal disputationer under redovisade verksamhetsår?
Antal kvinnor: Antal män: 2 PhD + 2 lic
helt finansierade av SSF: helt finansierade av SSF:
delfinansierade av SSF: delfinansierade av SSF: Yes