Patricie Heinrichova

Adamantane substitutions: a path to high-performing, soluble, versatile and sustainable organic semiconducting materials

Novel ethyladamantyl solubilization side groups were found to induce π–π interactions between the conjugated cores through adamantyl–adamantyl stacking in soluble diketopyrrolopyrrole (DPP) derivatives. The closeness of the DPP cores amplifies charge transfer in the material, as far as the π–π interaction is a dominant charge-hopping pathway. As a result, tenfold enhancement of hole mobilities exceeding those obtained for insoluble derivatives was reached. Moreover, due to high crystallinity and co-planarity of the conjugated cores, electron transfer was preserved with a mobility of 0.2 cm2 V−1 s−1 for dithiophene-DPP. At the same time, the material remained soluble, which is a significant advantage for purification and processing. This approach can be universally applied for many types of semiconducting organic materials containing the imide motif, where solubilization is achieved by side-group substitution.

UV-cured TiO2 electron transport layers for printable solar cells

This article is focused on the development of new formulations of inks for printed electron transport layers based on titanium oxide. The electron transport layers were prepared from a suspension consisting of titania nanoparticles and a novel organo-silica binder. The layers are post-processed by low temperature UV curing instead of thermal annealing. The UV-cured TiO2 layers were applied in inverted-structure organic bulk heterojunction solar cells with the active layer from a PCDTBT:PC60BM blend. These devices achieved a power conversion efficiency comparable to devices with TiO2 layers prepared by the common sol–gel process relying on high-temperature calcination. Thus the novel UV curable TiO2 formulation is promising as printable electron transport layers for flexible devices, which are not compatible with thermal processing.

Reducing Recombination Processes in the Inverted-Solution-Processed Small-Molecule Solar Cells by the Inserted Fullerene Cathode

Inverted architecture organic solar cells are potentially attractive, due to their long-term stability. However, this type of architecture is poorly applied in small-molecule solar cells, due to lower power conversion efficiencies (PCEs), usually caused by low fill factors. Here, the initially low fill factor of the inverted architecture small-molecule solar cells based on a DPP(TBFu)2:PC60BM blend is augmented by the inserted fullerene layer at the cathode, thus resulting in the efficient charge extraction and, up to now, highest PCE for DPP(TBFu)2 material and one of the highest for small-molecule DPP derivatives. Highly reproducible devices with PCE up to 5.29% were fabricated, which is notably higher than previously reported results.

The influence of transport layers on the photodegradation stability of polymer solar cell structures

Abstract A light exposure degradation study of electrically active polymers – high-glass-transition-temperature poly(1,4-phenylenevinylene) (Tg-PPV); poly(3-hexylthiophene-2,5-diyl) (P3HT); and poly(2-methoxy-5-(3′-7′- dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV) – in pure form and blends with [6,6]-phenyl C61-butyric acid methyl ester (PCBM) was conducted to assess the influence of the employed transport layers on the materials’ photodegradation stability. Devices were prepared on quartz glass and silicon (Si) substrates with a transport layer prepared from poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) or titanium dioxide (TiO2). Photodegradation processes in ambient air demonstrated that the polymers were thermally stable in the dark; thus, the material deteriorations not only were caused by thermal stress, but also from light-induced processes. Degradation processes of pure polymers may be considered as fast – in the order of hours – but retardable by blending of polymers with PCBM. The deposition of polymer blends on an additional layer of PEDOT:PSS or TiO2 revealed that the polymer blends studied in this work (except for P3HT) presented higher stability against polymer chain scission when deposited onto the TiO2 layer. Kinetic analysis undertaken during this work revealed that the photodegradation processes were followed by two degradation steps. Degradation kinetics were evaluated according to a Perrin-like model for absorption assessments and according to simple exponential for emission measurements.

Novel Riboflavin-Inspired Conjugated Bio-Organic Semiconductors

Flavins are known to be extremely versatile, thus enabling routes to innumerable modifications in order to obtain desired properties. Thus, in the present paper, the group of bio-inspired conjugated materials based on the alloxazine core is synthetized using two efficient novel synthetic approaches providing relatively high reaction yields. The comprehensive characterization of the materials, in order to evaluate the properties and application potential, has shown that the modification of the initial alloxazine core with aromatic substituents allows fine tuning of the optical bandgap, position of electronic orbitals, absorption and emission properties. Interestingly, the compounds possess multichromophoric behavior, which is assumed to be the results of an intramolecular proton transfer.

Vacuum-deposited diphenyl-diketo-pyrrolopyrrole solar cell structures

Photoelectrical parameters were measured of solar cell ITO|PEDOT:PSS|composite| Al samples. The active composite film was deposited in vacuum by co-evaporation of 3,6-bis(5-(benzofuran-2-yl)thiophen-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP(TBFu)2) and fullerene (C60). Additional DPP(TBFu)2:C60 composite films were studied by spectroscopy in the ultraviolet and visible region (UV-VIS) and scanning electron microscopy (SEM). It was found that solvent annealing (SVA) of composite DPP(TBFu)2:C60 vacuum-deposited films with tetrahydrofuran vapors improves the solar cell parameters by increasing the efficiency more than tenfold. This could be related to the more homogenized structure of the SVA composite film, as observed by SEM. The increased light absorption, as shown by UV-VIS spectroscopy, around the peak at 350 nm contributed to the better SVA solar cell performance. Photogeneration in the samples follows a monomolecular mechanism.

Photoelectric characterization of thin vacuum deposited diphenyl-diketo-pyrrolopyrroles films

The modern organic semiconductor devices are designed and fabricated as multilayer structures with stacked organic/inorganic thin films. There are strong requirements to the properties of the particular films comprising such structure, e. g. film homogeneity, thickness uniformity and roughness. Physical Vacuum Deposition (PVD) technique fulfils all of these requirements and even has the capability to produce the whole multilayer structure in the same vacuum cycle. Diphenyl-diketo-pyrrolopyrroles (DPP) are low molecular weight materials with promising luminescence and photoelectrical properties. Current paper deals with PVD of thin DPP films and investigation of their photoelectric properties. The organic films and inorganic electrodes of the multilayer structures were prepared in the same vacuum cycle, and then the samples were encapsulated in a glove box without exposure to oxygen. ITO|DPP|Al structures of about 150 nm thicknesses were prepared. The surface morphology of the films was studied by SEM imaging. Photoelectric characterization consisted of spectral sweep of the generated photocurrent, I-V characteristics in dark and under illumination and intensity sweep of the photocurrent for a given wavelength. Photoelectrical properties were successfully demonstrated and directions toward performance improvements have been given.

Thin polyphenylene vinylene electrophoretically and spin-coated films ? photoelectrical properties

Electrophoretic deposition (EPD) and spin coating (SC) techniques were compared on poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) used as a model material. Absorption spectra measured in a toluene solution and a toluene/ acetonitrile suspension with the same MDMO-PPV concentration of 0.0033 g.l?1 were analysed. An observed broadening of the characteristic absorption peak could be related to the formation of tightly-folded polymer chains in the suspension. Thin films of about 300 nm thickness were prepared by EPD from suspension and SC from solution with a concentration of 0.0033 g.l?1 and 8.95 g.l?1, respectively. The ITO|MDMO-PPV|Al structures with EPD MDMO-PPV films behave as a photovoltaic cell, while the same sample configuration with SC MDMO-PPV films acts more like a photoresistor. EPD and SC films exhibit the same charge-carrier photogeneration mechanism. It was clearly demonstrated that the EPD method uses the deposited material more efficiently, producing films with better photoelectrical properties.