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Free-standing and flexible field-effect transistors based on 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene)/polystyrene bilayers are obtained by well-controlled phase separation of both components. The phase separation is induced by solvent vapor annealing of initially amorphous blend films, leading to crystallization of TIPS-pentacene as the top layer. The crystallinity and blend morphology strongly depend on the molecular weight of polystyrene, and under optimized conditions, distinct phase separation with a well-defined and trap-free interface between both fractions is achieved. Due to the distinct bilayer morphology, the resulting flexible field-effect transistors reveal similar charge carrier mobilities as rigid devices and additionally pronounced environmental and bias stress stabilities. The performance of the flexible transistors remains stable up to a strain of 1.8%, while above this deformation, a close relation between current and strain is observed that is required for applications in strain sensors.

A series of new bis(benzo[h]quinolinato) Ir(III) complexes with modified β-ketoiminato ancillary ligands were synthesized, and their electrochemical, photophysical properties were determined with the support of theoretical calculations. Moreover, all the synthesized heteroleptic Ir(III) complexes were examined as dopants of the host–guest type emissive layers in solution-processed phosphorescent organic light emitting diodes (PhOLEDs) of a simple structure. As expected on the basis of voltammetry measurements as well as DFT calculations, all the compounds appeared to be green emitters. Their examination showed that alteration of β-ketoiminato ligand structure causes frontier orbitals’ energy levels to be slightly changed, while significantly affecting photoluminescence and electroluminescence efficiencies of iridium phosphors containing these ligands. It was also found that modification of ancillary ligands might enhance charge trapping on the dopant, thus increasing its efficiency, especially in electroluminescence. From among the iridium complexes studied, the compound bearing 1-naphthyl group bonded to the nitrogen atom of the ancillary ligand proved to be the most efficient emitter. The PhOLED fabricated on the basis of this dopant has reached a luminance level of 16000 cd/m2, current efficiency close to 12 cd/A, and an external quantum efficiency around 3.2%.

Recently, non-fullerene n-type organic semiconductors have attracted significant attention as acceptors in organic photovoltaics (OPVs) due to their great potential to realize high-power conversion efficiencies. The rational design of the central fused ring unit of these acceptor molecules is crucial to maximize device performance. Here, we report a new class of non-fullerene acceptor, Y6, that employs a ladder-type electron-deficient-core-based central fused ring (dithienothiophen[3.2-b]- pyrrolobenzothiadiazole) with a benzothiadiazole (BT) core to fine-tune its absorption and electron affinity. OPVs made from Y6 in conventional and inverted architectures each exhibited a high efficiency of 15.7%, measured in two separate labs. Inverted device structures were certified at Enli Tech Laboratory demonstrated an efficiency of 14.9%. We further observed that the Y6-based devices maintain a high efficiency of 13.6% with an active layer thickness of 300 nm. The electron-deficient-core-based fused ring reported in this work opens a new door in the molecular design of high-performance acceptors for OPVs.

The investigation of nondoped exciplex blends of 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), working as the one-electron acceptor molecule, with different electron donors is reported. The emissions of these exciplexes span from the blue to orange-red regions, showing clear contribution from thermally activated delayed fluorescence (TADF) and delayed fluorescence originated from nongeminate recombination of charge carriers created by the dissociation of optically generated exciplexes. We focus our studies on the properties of TADF in these systems, covering in particular the physical meaning of the different transient components observed in their luminescence decays. Our results unravel the intricate role of reverse intersystem crossing due to spin–orbit coupling and possibly also due to hyperfine interactions and internal conversion, which affect the efficiency of the TADF mechanism. Remarkable performances are obtained in prototype organic light-emitting diodes fabricated with some of these blends. Green exciplex blends, in particular, exhibited the current efficiency of 60 cd A–1, power efficiency of 71 lm W–1, and external quantum efficiency of 20%. We believe that our results will contribute significantly to highlight the potential advantages of intermolecular exciplexes in the area of organic light-emitting diodes.

Two conjugated polymers, with different side chains of alkoxy-substituted difluorobenzene and alkyl-substituted difluorobenzene based on quinoxaline (Qx) as the electron acceptor unit and benzodithiophene as the electron donor unit, named HFQx-T and HFAQx-T, were used as electron donor polymers to fabricate all-polymer solar cells (all-PSCs) with a naphthalenediimide–bithiophene n-type semiconducting polymer (N2200). Usually, halogenated solvents are harmful to natural environment and human beings, and solvent additives were disadvantageous in the process of roll-to-roll technology. The Qx-based polymers are successfully used to fabricate high-performance all-PSCs, which processed with the nonhalogenated solvent tetrahydrofuran (THF) at room temperature. With THF as the processing solvent, the active layer showed a higher absorption coefficient, better phase separation, exciton dissociation, and charge carrier mobilities than that processed with CHCl3. Moreover, the photovoltaic properties have been dramatically improved with THF. The optimized device of HFAQx-T:N2200 processed with THF delivered an efficient power conversion efficiency (PCE) of 7.45%, which is the highest PCE for all-PSCs from Qx-based polymers processed by a nonhalogenated solvent.

Photogeneration of charge carriers in closely packed phenyl-C61-butyric acid methyl ester (PCBM) was investigated by means of the xerographic discharge technique. It was found that the position of the center of mass of the thermalized electron is positioned at a distance that is integral to the multiplicity of the center-to-center distance between the adjacent PCBM molecules. For a low electric field, 104–107V/m, the most photogenerated electrons originate from the electrons thermalized at the molecule next but one to the geminate recombination center. For the threshold electric field (ca. 2 × 108V/m) the expected value of the thermalization length, ca. 1.9 nm, is independent of the assumed distribution functions of thermalization distance of the electron–hole pairs. The Coulomb binding energy for this characteristic of PCBM electron–hole separation length is correlated with the threshold energy value separating the extrinsic and intrinsic photogeneration in fullerenes. The model predicts the observed experimentally threshold value of photon energy 2.25 eV, below which the photogeneration yield in fullerene-based materials decreases abruptly; then, taking into account the average electron–hole pair Coulomb binding energy 0.15 eV, one can calculate the electric gap energy 2.4 eV, consistent with the literature data. It explains also how the presence of poly(3-hexylthiophene) influences the photogeneration process.

Ambipolar organic field-effect transistors (OFETs) based on heterojunction active films still suffer from an imbalance in the transport of electrons and holes. This problem is related to an uncontrolled phase separation between the donor and acceptor organic semiconductors in the thin films. In this work, we have developed a concept to improve the phase separation in heterojunction transistors to enhance their ambipolar performance. This concept is based on preaggregation of the donor polymer, in this case poly(3-hexylthiophene) (P3HT), before solution mixing with the small-molecular-weight acceptor, phenyl-C61-butyric acid methyl ester (PCBM). The resulting heterojunction transistor morphology consists of self-assembled P3HT fibers embedded in a PCBM matrix, ensuring balanced mobilities reaching 0.01 cm2/V s for both holes and electrons. These are the highest mobility values reported so far for ambipolar OFETs based on P3HT/PCBM blends. Preaggregation of the conjugated polymer before fabricating binary blends can be regarded as a general concept for a wider range of semiconducting systems applicable in organic electronic devices.

A series of solution-processable tetraalkoxy-substituted dinaphtho[2,3-a:2′,3′-h]phenazines were synthesized by reductive functionalization of indanthrone (6,15-dihydrodinaphtho[2,3-a:2′,3′-h]phenazine-5,9,14,18-tetraone), an old intractable dye. The melting point of these new compounds was found to decrease from 204 °C to 98 °C upon extension of the number of carbons from 4 to 12 in the alkoxy substituent. All derivatives show a strong tendency to self-organize in 2D as evidenced by STM investigations of monolayers deposited on HOPG. The 2D structure is less dense and shows different alkoxy group interdigitation pattern as compared to the 3D structure determined from the X-ray diffraction data obtained for the corresponding single crystals. Electrochemical, absorption, and emission properties of tetraalkoxy-substituted dinaphtho[2,3-a:2′,3′-h]phenazines, studied in solution, are essentially independent of the length of the alkoxy substituents. All derivatives exhibit high photoluminescence quantum yield, approaching 60%. When molecularly dispersed in a solid matrix consisting of poly(9-vinylcarbazole) (PVK) (60 wt %) and (2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole) (PBD) (40 wt %) (so-called “guest/host configuration”), they show green electroluminescence due to an effective energy transfer from the matrix to the luminophore. The best light-emitting diodes were obtained for the butoxy derivative showing a luminance approaching 1500 cd/m2and a luminous efficiency over 0.8 cd/A.

In organic electronics solution‐processable n‐channel field‐effect transistors (FETs) matching the parameters of the best p‐channel FETs are needed. Progress toward the fabrication of such devices is strongly impeded by a limited number of suitable organic semiconductors as well as by the lack of processing techniques that enable strict control of the supramolecular organization in the deposited layer. Here, the use of N,N′‐bis(4‐n‐butylphenyl)‐1,4,5,8‐naphthalenetetracarboxylic‐1,4:5,8‐bisimide (NBI‐4‐n‐BuPh) for fabrication of n‐channel FETs is described. The unidirectionally oriented crystalline layers of NBI‐4‐n‐BuPh are obtained by the zone‐casting method under ambient conditions. Due to the bottom‐contact, top‐gate configuration used, the gate dielectric, Parylene C, also acts as a protective layer. This, together with a sufficiently low LUMO level of NBI‐4‐n‐BuPh allows the fabrication and operation of these novel n‐channel transistors under ambient conditions. The high order of the NBI‐4‐n‐BuPh molecules in the zone‐cast layer and high purity of the gate dielectric yield good performance of the transistors.

We report on the preparation of high performance field-effect transistors (FETs) based on large areas of aligned films of a TTF derivative, namely, tetrakis-(octadecylthio)-tetrathiafulvalene (TTF-4SC18). TTF-4SC18 assembles into one-dimensional stacks in which the long alkyl chains promote intermolecular − overlapping due to their extremely closely packed nature. The films were prepared from solution by zone-casting, a simple technique that does not require the use of preoriented substrates. The films were characterized by AFM and X-ray, indicating an extremely high crystalline quality. The TTF molecules are tilted with respect to the substrate surface and are well-aligned in the casting direction. More than 40 FETs were measured, showing a remarkable reproducibility of their performance. The average charge carrier mobility value measured along the casting direction was about 0.006 cm2/V s for a channel length L 100 m and about 0.01 cm2/V s for L 80 m and L 50 m. The FET mobilities determined in the direction perpendicular to the orientation were ca. 1 order of magnitude lower. We found that all the devices after annealing exhibited an enhanced performance with FETs mobilities about 1 order of magnitude higher. The best devices revealed a charge carrier mobility close to 0.1 cm2/V s with an on/off ratio of the order of 104.

Summary: Photopolymerisation of acrylic acid (AA) to poly(acrylic acid) (polyAA) in the lyotropic liquid crystalline (LLC) phase of hydroxypropylcellulose (HPC) in the AA-water mixture, as well as the influence of mesomorphic organisation of the HPC on the structure of water was studied. Raman and thermo-optical analysis results reveal that the lyotropic phase of the HPC/AA-H2O can be used as a template system suitable for the formation of anisotropic hydrogels. The mesomorphic organisation of the HPC/AA-H2O phase is preserved after photopolymerisation induced by UV radiation. Also the structure of water, strongly disturbed in the LLC‐phase as compared with the structure of liquid water, is preserved after the photopolymerisation. Apart from the water originating from the LLC‐phase of HPC/AA‐H2O, the anisotropic hydrogel may also contain water molecules taken up during immersion of the hydrogel in liquid water. Raman spectroscopy reveals that the water resulting from the swelling has a structure close to that of liquid water. Because the anisotropic hydrogel network is created by hydrogen bonds between HPC, water and polyAA, it is not stable when immersed in water for long time. An increased stability of the LC‐organisation of the hydrogel network can be achieved by crosslinking of the hydrogel with calcium ions, which can form a salt with polyAA, as confirmed by Raman spectroscopy.Comparison of the (a) Raman spectrum of liquid water with (b) that of water in the hydrogel, illustrating the influence of the mesomorphic organization in the hydrogel on the water structure.

A series of poly{[3-(carbazol-9-yl)propyl]silane-co-methylphenylsilane}s were investigated by optical absorption, photoluminescence and thermoluminescence measurements. It was found that the optical absorption bands of the carbazolyl side groups superimpose on those of the Si backbones in the ultraviolet range. This feature reduces photodegradability of Si-Si bonds during UV irradiation. The TL spectra recorded in the 15 - 325 K temperature range after photoexcitation at 15 K show that the carbazolyl side groups act as trapping sites in polysilanes. Increasing density of carbazolyl groups results in increasing population of deeper (ca. 150 meV) traps. Spectral analyses of the thermoluminescence at different temperatures are discussed and compared with analogous results for poly(9-vinylcarbazole) (PVK). It is concluded that the monomeric mechanism of luminescence dominates at low temperatures while the excimeric mechanism prevails at higher temperatures, similarly to PVK.

A series of poly{[3‐(carbazol‐9‐yl)propyl]silane‐co‐methylphenylsilane}s were investigated by optical absorption, photoluminescence and thermoluminescence measurements. It was found that the optical absorption bands of the carbazolyl side groups superimpose on those of the Si backbones in the ultraviolet range. This feature reduces photodegradability of Si‐Si bonds during UV irradiation. The TL spectra recorded in the 15 ‐ 325 K temperature range after photoexcitation at 15 K show that the carbazolyl side groups act as trapping sites in polysilanes. Increasing density of carbazolyl groups results in increasing population of deeper (ca. 150 meV) traps. Spectral analyses of the thermoluminescence at different temperatures are discussed and compared with analogous results for poly(9‐vinylcarbazole) (PVK). It is concluded that the monomeric mechanism of luminescence dominates at low temperatures while the excimeric mechanism prevails at higher temperatures, similarly to PVK.

The modern technologies use many multilayer composites comprising, the connection of different classes substrates: ceramics, metals, polymers, etc. In this work we focused our attention on an application of confocal micro-Raman spectroscopy to study the multilayer composites. Different multilayer model systems were used to check the role of the confocal mode. The problem of the transparency of layer, and their thickness were discussed. The procedure of determination of interfaces from so-called depth profiles and their first derivatives was also presented.

The modern technologies use many multilayer composites comprising, the connection of different classes substrates: ceramics, metals, polymers, etc. In this work we focused our attention on an application of confocal micro‐Raman spectroscopy to study the multilayer composites. Different multilayer model systems were used to check the role of the confocal mode. The problem of the transparency of layer, and their thickness were discussed. The procedure of determination of interfaces from so‐called depth profiles and their first derivatives was also presented.

AbstractThe molecular relaxation phenomena of the specific polymer composites obtained by photopolymerisation of the oriented lyotropic liquid-crystalline systems composed of cellulose derivatives dissolved in photo-polymerisable acrylic acid are studied. We have investigated the composites based on two cellulose derivatives, which differ by the length of their side-chains and consequently by their physical properties.In this work, the molecular relaxations of such aniso- tropic composites were studied by dielectric relaxation spectroscopy and by thermooptical analysis. In the dielectric relaxation spectroscopy two representations were analysed: temperature dependences of dielectric loss ϵ“(T) and of electric modulus M“(T). The electric modulus representation is especially convenient to monitor the relaxations in a high temperature range where the ionic conductivity dominates the dielectric response.

The low-frequency Raman scattering (LFRS) was used in order to determine the orientation of poly(acrylic acid) in anisotropy composite with liquid crystalline [(propionyloxy)propyl]cellulose (PPC). The photopolymerisation of acrylic acid in the presence of PPC leads to the formation of the poly(acrylic acid) (pAA) anisotropic network. This anisotropy is stable even at temperatures higher than the temperature of the optical isotropisation of the PPC/pAA composite. The comparison of the LFRS and thermooptical data proves the hypothesis explaining of the reversibility of the optical birefringence in the PPC/pAA composites by formation, in a course of photopolymerisation of anisotropic pAA network.

The curing of different epoxy-amine model systems which present only gelification and/or vitrification processes has been followed with the evolution of their viscoelastic and electrical behaviours during the network formation. Some attempts are performed to correlate the significant evolution of the mechanical and electrical parameters with the physico-chemical changes of these well defined chemical systems during their hardening and complete curing.

The method of reticulate doping previously used to obtain bulk-conducting macromolecular films is modified to yield surface-conducting materials. Morphology and properties of these systems, consisting of a conducting network of CT complex crystallites penetrating the bulk of an inert polymer matrix are briefly described, most of them being supposed to be common for bulk and surface-conducting films. Preparation of surface conducting films is discussed in terms of crystallization of the components of the CT complex initially molecular ly dispersed in the matrix due to a controlled increase of the molecular mobility in the surface layer of the film. Possible mechanisms responsible for the unusual effectiveness of the reticulate doping are discussed.