Dynamically altered conductance in an Organic Thin Film Memristive Device

The memristive device is one of the basic elements of novel, brain-inspired, fast, and energy-efficient information processing systems in which there is no separation between memorization and information analysis functions. Since the first demonstration of the resistive switching effect, several types of memristive devices have been developed. In most of them, the memristive effect originates from direct modification of the conducting area, e.g. conducting filament formation/disintegration, or semiconductor doping/dedoping. Here, we report a solution-processed lateral memristive device based on a new conductivity modulation mechanism. The device architecture resembles that of an organic field-effect transistor in which the top gate electrode is replaced with an additional insulator layer containing mobile ions. Alteration of the ion distribution under the influence of applied potential changes the electric field, modifying the conductivity of the semiconductor channel. The devices exhibit highly stable current-voltage hysteresis loops and Short-Term Plasticity (STP). We also demonstrate short-term synaptic plasticity with tunable time constants

Temperature- and pH-responsive schizophrenic copolymer brush coatings with enhanced temperature response in pure water

Novel brush coatings were fabricated with glass surface-grafted chains copolymerized using surface-initiated atom transfer radical polymerization (SI-ATRP) from 2-(2-methoxyethoxy)ethyl methacrylate (OEGMA188) and acrylamide (AAm), taken in different proportions. P(OEGMA188-co-AAm) brushes with AAm mole fraction >44% (determined with XPS and TOF-SIMS spectroscopy) and nearly constant with the depth copolymer composition (TOF-SIMS profiling) exhibit unusual temperature-induced transformations: The contact angle of water droplets on P(OEGMA188-co-AAm) coatings increases by ~45° with temperature, compared to 17−18° for POEGMA188 and PAAm. The thickness of coatings immersed in water and the morphology of coatings imaged in air show a temperature response for POEGMA188 (using reflectance spectroscopy and AFM, respectively), but this response is weak for P(OEGMA188-co-AAm) and absent for PAAm. This suggests mechanisms more complex than a simple transition between hydrated loose coils and hydrophobic collapsed chains. For POEGMA188, the hydrogen bonds between the ether oxygens of poly(ethylene glycol) and water hydrogens are formed below the transition temperature T$_{c}$ and disrupted above T$_{c}$ when polymer−polymer interactions are favored. Different hydrogen bond structures of PAAm include free amide groups, cis-trans-multimers, and trans-multimers of amide groups. Here, hydrogen bonds between free amide groups and water dominate at T T$_{c}$, such as cis-trans-multimers and trans-multimers of amide groups, can still be hydrated. The enhanced temperature-dependent response of wettability for P(OEGMA188-co-AAm) with a high mole fraction of AAm suggests the formation at T$_{c}$ of more hydrophobic structures, realized by hydrogen bonding between the ether oxygens of OEGMA188 and the amide fragments of AAm, where water molecules are caged. Furthermore, P(OEGMA188-co-AAm) coatings immersed in pH buffer solutions exhibit a 'schizophrenic' behavior in wettability, with transitions that mimic LCST and UCST for pH = 3, LCST for pH = 5 and 7, and any transition blocked for pH = 9

Synthesis and characterization of two new TiO2-containing benzothiazole-based imine composites for organic device applications

The effect of the presence of titanium dioxide in two new imines, (E,E)-(butane-1,4-diyl)bis(oxybutane-4,1-diyl) bis(4- {[(benzo[d][1,3]thiazol-2-yl)methylidene]amino}benzoate) (SP1) and (E)-N-[(benzo[d][1,3]thiazol-2-yl)methylidene]-4-dodecylaniline (SP2), on the properties and stability of imine:TiO2 composites for organic device applications were examined. The investigated titanium dioxide (in anatase form, obtained via the sol–gel method) exhibited a surface area of 59.5 m2 /g according to Brunauer–Emmett–Teller theory, and its structure is a combination of both meso- and microporous. The average pore diameter calculated by the Barrett–Joyner–Halenda method was 6.2 nm and the cumulative volume of pores was 0.117 m3 /g. The imine SP1 exhibited columnar organization (Col), while SP2 revealed a hexagonal columnar crystalline phase (Colhk). The imine:TiO2 mixtures in various weight ratio (3:0, 3:1, 3:2, 3:3) showed a lower energy gap and HOMO–LUMO energy levels compared to pure TiO2 . This implies that TiO2 provides not only a larger surface area for sensitizer adsorption and good electron collection, but also causes a shift of the imine energy levels resulting from intermolecular interaction. Also the temperature of the phase transition was slightly affected with the increase of TiO2 concentration in imine-based composites. The changes observed in the Fourier transform middle-infrared absorption (FT-MIR) spectra confirmed the significant influence of TiO2 on structural properties of both investigated imines. Similar interactions of oxygen vacancies existing on the TiO2 surface with SP1 and SP2 were observed. The imine:TiO2 mixtures showed good air stability and reusability, which demonstrates its potential for organic device applications

Synthesis and characterization of two new TiO2-containing benzothiazole-based imine composites for organic device applications

The effect of the presence of titanium dioxide in two new imines, (E,E)-(butane-1,4-diyl)bis(oxybutane-4,1-diyl) bis(4- {[(benzo[d][1,3]thiazol-2-yl)methylidene]amino}benzoate) (SP1) and (E)-N-[(benzo[d][1,3]thiazol-2-yl)methylidene]-4-dodecylaniline (SP2), on the properties and stability of imine:TiO2 composites for organic device applications were examined. The investigated titanium dioxide (in anatase form, obtained via the sol–gel method) exhibited a surface area of 59.5 m2/g according to Brunauer–Emmett–Teller theory, and its structure is a combination of both meso- and microporous. The average pore diameter calculated by the Barrett–Joyner–Halenda method was 6.2 nm and the cumulative volume of pores was 0.117 m3/g. The imine SP1 exhibited columnar organization (Col), while SP2 revealed a hexagonal columnar crystalline phase (Colhk). The imine:TiO2 mixtures in various weight ratio (3:0, 3:1, 3:2, 3:3) showed a lower energy gap and HOMO–LUMO energy levels compared to pure TiO2. This implies that TiO2 provides not only a larger surface area for sensitizer adsorption and good electron collection, but also causes a shift of the imine energy levels resulting from intermolecular interaction. Also the temperature of the phase transition was slightly affected with the increase of TiO2 concentration in imine-based composites. The changes observed in the Fourier transform middle-infrared absorption (FT-MIR) spectra confirmed the significant influence of TiO2 on structural properties of both investigated imines. Similar interactions of oxygen vacancies existing on the TiO2 surface with SP1 and SP2 were observed. The imine:TiO2 mixtures showed good air stability and reusability, which demonstrates its potential for organic device applications

Mutual Diffusion of Model Acceptor/Donor Bilayers under Solvent Vapor Annealing as a Novel Route for Organic Solar Cell Fabrication

The fabrication of bulk heterojunction organic solar cells (OSCs) is primarily based on a phase demixing during solution deposition. This spontaneous process is triggered when, as a result of a decrease in the solvent concentration, interactions between donor and acceptor molecules begin to dominate. Herein, we present that interdiffusion of the same molecules is possible when a bilayers of donors and acceptors are exposed to solvent vapor. Poly(3-hexyl thiophene) (P3HT), and poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT) were used as donors and two types of fullerene derivatives were used as acceptors: phenyl-C61-butyric acid methyl ester (PC60BM) and phenyl-C71-butyric acid methyl ester (PC70BM), Secondary ion mass spectrometry depth profiling revealed that the interpenetration of donors and acceptors induced by solvent vapor annealing was dependent on solvent vapor and component compatibility. Exposure to chloroform vapor resulted in a complete intermixing of both components. The mutual mixing increased efficiency of inverted solar cells prepared by solvent vapor annealing of model donor/acceptor bilayers. These results provide a new means for mixing incompatible components for the fabrication of organic solar cells

Interdiffusion of fullerene derivative in PQT-12 thin layer under solvent annealing.

Aby osiągnąć wysoką wydajność foto-konwersji, niezbędne jest głębsze zrozumienie mechanizmów dyfuzyjnych w warstwie aktywnej ogniw słonecznych. Wydajność jest silnie zależna od przestrzennego ułożenia komponentów tworzących warstwę aktywną. Powszechnie używane układy wykorzystują warstwę złożoną z pochodnej fullerenu C60 i poli(3-alkilotiofenów). Te dwa składniki powinny przenikać się wzajemnie aby zwiększyć powierzchnię kontaktu ( utworzyć strukturę zwaną heterozłączem objętościowym -BHJ). Optymalna geometria BHJ osiągana jest poprzez wygrzewanie temperaturowe lub rozpuszczalnikowe. W niniejszej pracy badane były dwuwarstwy utworzone z poli(3,3''' didodecylo quatro tiofenu)(PQT-12) i pochodnych fullerenu C60.In order to achieve high photoconversion efficiencie, it is necessary to better understand the diffusion mechanisms in the active layer of solar cells. The efficiency is highly dependent on the spatial arrangement of the components forming the active layer. Most common used system are layers consisting phases of C60 fullerene derivative and poly (3-alkilo thiophene). This two phases should interpenetrate to increase the interface area (create structure called bulk heterojunction BHJ). BHJ optimal shape can be obtained using thermal or vapor solvent annealing. In this research the bilayer of of poly (3,3”’ didodecyl quarter thiophene) (PQT 12) and C60 fullerene derivative was analyzed

The influence of synthetic polymers’ chemical structures on the sputtering rate of low-energy ion beams

Metoda spektroskopii masowej jonów wtórnych jest użytacznym narzędziem w badaniach nad cienkimi warstwami polimerowymi. Istotnym czynnikiem w tej metodzie jest analiza procesów zachodzących podczas rozpylania jonowgo. Celem niniejszej pracy było zbadanie wpływu budowy chemicznej wybranych polimerów syntetycznych na szybkość ich rozpylania. Kluczowym aspektem branym pod uwagę był wpływ obecności tlenu na proces rozpylania polimerów.Secondary ion mass spectroscopy is widely used in research on the polymer thin films. The analysis of processes during ion sputtering is an important aspect of SIMS method. The aim of this work is to present the impact of chemical structure of selected synthetic polymers on the sputtering rate. The key factor in this comparison was the influence of oxygen on the polymer thin films’ sputtering process