Mattias Svensson

Correlation between oxidation potential and open-circuit voltage of composite solar cells based on blends of polythiophenes/ fullerene derivative

The photovoltaic parameters of donor/acceptor blend organic solar cells are highly influenced by several parameters, such as the strength of the acceptor species, the morphology of the film due to ...

Substituted polythiophenes designed for optoelectronic devices and conductors

Polythiophenes are a very versatile class of conjugated polymers. Substituted polythiophenes can be tailored for various applications by designing the side groups to give the polymer different desired properties. Our work on preparing polythiophenes designed to have high stability in the doped state is described. We also discuss our efforts on tuning the colour of the emission from polythiophenes for use in polymer light-emitting diodes. Design criteria for the synthesis of polythiophenes with high luminescence efficiency for use in light-emitting diodes and lasers are also described. Finally, the design of polythiophenes for use in photodiodes is discussed.

Trapping Light in Polymer Photodiodes with Soft Embossed Gratings

Increasing the conversion efficiency is very important in photovoltaic devices, as is cheap and simple technology. Here is demonstrated a soft embossing technique for printing a submicrometer grati ...

Influence of buffer layers on the performance of polymer solar cells

The study of the influence of different anode buffer layers on the performance of solar cells based on blends of polyfluorene copolymers, acting as electron donor, and [6,6]-phenyl-C61-butyric acid ...

Polymer Photovoltaic Devices from Stratified Multilayers of Donor–Acceptor Blends

phase the anode and for the acceptor phase the cathode. This is not quite compatible with the more-or-less sharp interfaces found in bilayer photodiodes where a fullerene or other acceptor is evaporated on top of a polymer layer. If we wanted to make stratified but inter-diffused structures, a common solvent would hinder the utilization of these preparation methods for the fabrication of sharp multilayers. The application of special conditions during the spin-coating, however, makes it possible to obtain diffuse bilayer structures from soluble organic molecules and polymers. In this letter we present our attempts to combine the advantages of the interpenetrating network morphology in blends with the advantages of the bilayer structures, in order to obtain high fill-factor values in devices. This reflects the good conditions for charge collection and transport, which are essential for the realization of efficient

Photophysics of thiophene based polymers in solution: The role of nonradiative decay processes

An investigation has been undertaken of the photophysics of six thiophene-based polymers. This includes the measurement of fluorescence quantum yields, quantum yields for triplet formation, and determination of fluorescence and triplet lifetimes in benzene solution at room temperature. From the above-mentioned data, the overall set of rates for the deactivation processes (fluorescence, intersystem crossing, and internal conversion), has been evaluated. Mechanisms of nonradiative decay are discussed, and it is shown that both intersystem crossing and internal conversion are important in the decay of the lowest singlet excited state of isolated polythiophenes molecules in solution. Comparison of spectroscopic and photophysical properties of the polymers with analogous oligothiophenes shows that with the polymer, the S1⇝S0 internal conversion deactivation pathway plays a major role, in contrast to the behavior found with the oligomers where this internal conversion deactivation channel is essentially negligible.

Ultrafast photogeneration of inter-chain charge pairs in polythiophene films

Photoexcitation dynamics in films of polythiophenes with different side groups were studied by transient absorption spectroscopy using 80 fs pulses. We show that inter-chain charge pairs (CP) are generated with similar to 20% efficiency in a polymer with short inter-chain distance (similar to 4 Angstrom) within 100 fs after photoexcitation. We discuss two mechanisms for inter-chain charge separation: (i) electron or hole transfer from an initially excited intra-chain singlet state or (ii) optical excitation of mixed exciton-charge transfer states, which quickly evolve to inter-chain CPs

Electrochemical bandgaps of substituted polythiophenesElectronic supplementary information (ESI) available: cyclic voltammograms not given within the article. See http://www.rsc.org/suppdata/jm/b3/b301403g/

The electrochemical bandgaps for different soluble substituted polythiophenes have been measured by cyclic voltammetry. The effect of substituents on the oxidation/reduction potentials is discussed. Bandgaps obtained by cyclic voltammetry have been found to be in general higher than optical bandgaps. Among regioregular polymers substituted with a phenyl group at position 3 of the thiophene ring, examples are found that give very symmetric voltammograms. Rationalization for this behaviour is discussed from a conformational point of view.

Polyfluorene copolymer based bulk heterojunction solar cells

Bulk heterojunction solar cells based on blends of photoactive layers of polyfluorene copolymer Poly((2,7-(9-(2′-ethylhexyl)-9-hexyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole))-co-(2,7-(9-(2′-ethylhexyl)-9-hexyl-fluorene)-alt-2,5-thiophene)) (LBPF3) acting as electron donor, and [6,6]-phenyl-C61-butyric acid methylester (PCBM), acting as electron acceptor, were constructed and studied. The power conversion efficiency for a 1:4 (by weight) blend of LBPF3:PCBM under simulated solar light illumination having light intensity of 100 mW/cm2 was 1.7%, and 9.2% under monochromatic (565 nm) light illumination with light intensity of 0.145 mW/cm2. The maximum external quantum efficiency (incident photons to converted electrons) for this device was found to be above 40% from 400 to 560 nm. The effects of blend composition and film thickness on the photovoltaic parameters were also studied. The incident light intensity dependence of the short circuit current showed a linear relationship.

The effect of conjugation length on triplet energies, electron delocalization and electron–electron correlation in soluble polythiophenes

Triplet energies from a family of polythiophenes in which effective conjugation length is controlled by steric torsion have been measured for the isolated polymer chain regime, i.e., benzene solution. Triplet states are stabilized by some 0.6 eV as effective conjugation length increases up to ca. 6 repeat units, then saturation occurs. This triplet stabilization must occur by electron delocalization and implies that singlet states are stabilized as conjugation length increases by a combination of electron and exciton delocalization.