Optoelectronic Phenomena and Materials

Research People Equipment Publications

Research

The department consists of two groups, jointly working on the development of  new polymer and composite materials for electronic and optoelectronic active components. It is focused especially on organic photovoltaic cells, light-emitting diodes, electrical and optical sensors and organic field-effect transistors (OFETs) and for flexible printed electronics. The aim is to prepare these electronic components from soluble derivatives of dielectric, semiconductive or conductive polymers using inexpensive casting or printing techniques.

The basic research is focused on the phenomena of generation, transport, and recombination of free charge carriers, charge and energy transfer at the interfaces of organic materials or organic-inorganic heterojunctions, injection of charges from electrodes, photochromic transformation and on plasmonic phenomena in polymer composites with metal nanoparticles. Quantum chemical calculations and computer modeling are used to correlate the observed macroscopic properties with chemical structure and morphology of molecules. The transient optical absorption spectroscopy with time resolution of 30 fs is used to study the photophysical phenomena in early stage after photoexcitation. Such measurements are important for understanding and optimization of the solar energy conversion in organic photovoltaic solar cells. The laboratory is engaged in the development of the concept of molecular electronics, both on an experimental and theoretical level.

Significant advances were achieved in the development of the methods of preparation and understanding the properties of nanocomposites of plasmonic metal (silver and gold) nanoparticles embedded in matrices of conjugated polymers. A new research field has been opened on the nanocomposites with the p-conjugated polyelectrolyte (CPE) matrices. The main advantage of these systems is in the possibility of their solution processing from “green” solvents such as alcohols and water. It has been shown that the aggregation of nanoparticles in the environment of CPEs, as in highly regioregular cationic polythiophene polyelectrolyte can be controlled to obtain the nanocomposites containing "hot spots" with extreme local amplification of the optical field. The hot spots are formed within the fractal aggregates of nanoparticles and their presence was evidenced through their typical optical extinction and the strong Raman scattering enhancement. The results bring the possibility of preparing plasmonic nanocomposites of semiconducting polymers, in which various photophysical phenomena like the charge transfer and fluorescence can be enhanced or locally quenched. Plasmonic nanoparticles were successfully applied to enhance the conversion efficiency in bulk heterojunction solar cells (Fig.1).

 

Figure 1: The photon-to-electron conversion efficiency in bulk heterojunction organic photovoltaic cell can be enhanced by gold or silver nanoparticles.

 

The team recently performed femtosecond optical absorption studies of ω-bis(terpyridyl)oligothiophenes during their spontaneous assembling into conjugated constitutional dynamic polymers (dynamers), which might be utilized in optoelectronics. In another time resolved study the deactivation pathway of photoexcited state of a novel soluble nickel (II) phthalocyanine peripherally substituted with octabutoxy groups was observed. It was found that the photoexcitation evolves in two independent branches (Fig.2). In one of them, assigned to J-aggregates, the photoexcitation decayed to a triplet state with a very long lifetime. The finding is important for the applications that rely on singlet oxygen formation or fast non-radiative deactivation of the excited state, as for photoprotection or photodynamic therapy.

 

Figure 2: Relaxation pathway of the excitation energy in 2,3,9,10,16,17,23,24-octabutoxy nickel (II) phthalocyanine in solution.

 

The strong sensitivity of the electronic properties of organic materials to various analytes in the environment has been exploited to design printable organic sensors. A new electrochemical sensing cell for NO2 detection has been developed that combines the advantages of a solid polymer electrolyte (ionic-liquid plasticized PVDF) and a modified carbon indicator electrode. The system is currently used to evaluate organic catalysts to improve the accuracy and selectivity of gas-sensing electrodes. This “artificial nose” may be incorporated into multiple sensor arrays to monitor air quality in alarm systems for the detection of toxic gases. Good results were achieved with new soluble derivatives of metallophthalocyanines, particularly Zn-phthalocyanine (ZnPc) with sulfonamide side groups. ZnPc is suitable for thin-film preparation by printing, and its electrical conductivity and optical absorption are sensitive to various gases. ZnPc forms a charge transfer complex with NO2, which changes the absorption spectrum and increases electrical conductivity by two orders of magnitude (Fig. 3).

This result provides a foundation for the development of detectors for NO2, one of the most common environmentally polluting gases. ZnPc fulfils the demands for printed flexible electronics, which require cheap and reliable gas sensors composed of soluble organic sensing materials.

 

Figure 3: Electrochemical sensor printed on paper with responses to exposure of nitrogen dioxide

 

New model of the photogeneration of free charge carriers in polymers was developed with the assumption on the reversible resonant coupling of the localized excitation to the charge transfer states and, consequently, the dependence of internal parameters (permittivity, effective mass of the hole, rate constants) on electric field. The primary model was improved by the quantum chemical approach that incorporated the electron-hole potential and the charge delocalization effects of the charge transfer state, taking into account the discrete character of polymer transport sites, energetic disorder and reorganization effects in the polymer chain. This model of photogeneration allows a combination with our charge carrier mobility model for polymers.8  The calculated charge carrier concentration dependence of the mobility provides a unified description of the mobility for the low charge carrier concentration regime (as in photovoltaics) and accumulated concentration regime (OFET regime).

Figure. 4: Concentration dependence of the hole mobility in the crystalline and amorphous phases of poly(3-hexylthiophene-2,5-diyl) (P3HT) with a typical polycrystalline nanofibre structure calculated using the combined quantum-mechanical/semiclassical model developed in the department.

 

Cooperations:

Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler University Linz, Austria

Friedrich-Schiller-University Jena,Germany

Leibniz Institute of Polymer Research Dresden, Germany

Lodz University of Technology, Faculty of Chemistry, Poland

Wroclaw University of Technology, Poland

Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche, Bologna, Italy

Institute of Microelectronics, NCSR “Demokritos”., Athens, Greece

Warsaw University of Technology, Faculty of Chemistry, Poland

Charles University, Faculty of Science and Faculty of Mathematics and Physics, Prague

Faculty of Chemistry, Brno University of Technology

University of West Bohemia, Research Centre New Technologies, Plzeň

Faculty of Chemical Technology, University of Pardubice

Centre for Organic Chemistry Ltd., Pardubice, Czech Republic

 

Recent Fundings

“Flexible printed electronics based on organic and hybrid materials FLEXPRINT”, Centrum of competence, TAČR, 2012 - 2019.

“Study of electronic processes in molecular systems for organic photonics”, Czech Science Foundation (GAČR), 2015–2017.

"Conjugated Polymers for Organic Photovoltaics" , GAČR, 2012-2016.

„Electronic and optical properties of hybrid nanostructures“, MŠMT, LD14011 (HINT COST Action MP1202), 2014-2016.

"Advanced Polymers for Photonics",  GAČR, 2012-2015.  

“Polymeric composite materials for optoelectronic applications”, AV ČR, 2012–2015.

“Polyelectrolytic conjugated dynamers: preparation, constitutional dynamics and functional properties of new materials”, GAČR, 2012 – 2015.

“ECNP Growth”, EU Coordinated action, 2012-2015.

“Inovative molecular-electronic elements with charge trapping in the metal nanoparticles assemblies”, MSMT, 2012-2014.

"Engineering of surface-modified optical processes in molecules and semiconductor quantum dots by plasmon resonances in metal nanoparticle assemblies", project GACR, 2010 - 2014.

„Mechanism of energy a charge transfer in semiconductors“, MŠMT, KONTAKT LH II 121 86, 2012-2014.

“Photogeneration and charge transport in molecular semiconductors for organic photovoltaics”, GAČR, 2010–2013.

“Electronic transport in III-N-V compounds nanostructures”, MŠMT, COST OC 1007, 2010-2012.

EU Network of Excellence "FlexNet", 2010 – 2012.

BIOpolymer POstdoctoral Laboratory and educational center - BIOPOL

Otto Wichterle Centre of Polymer Materials and Technologies - CPMTOW

Centre of Biomedicinal Polymers - CBMP

Centre of Polymer Sensors - CPS

Polymers for Power Engineering - Energolab


 

Institute of Macromolecular Chemistry AS CR, v.v.i.
Heyrovského nám. 2
CZ-162 06 Praha 6
Czech Republic
phone:+420 296 809 111
fax:+420 296 809 410

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