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Microcrystals with different orientations of thiophene/phenylene co-oligomers (TPCOs) serving as Fabry–Perot microresonators were prepared using a miniemulsion technique with modification. Reflecting molecular packings and crystal structures, p-type 5,5′-bis(4-biphenylyl)-2,2′-bithiophene (BP2T) and n-type 5,5′-bis(4′-cyanobiphenyl-4-yl)-2,2′-bithiophene (BP2T-CN) grow in square-shaped (microplatelet) and rod-shaped (microrod) microcrystals, respectively. Strong exciton–photon coupling was demonstrated for BP2T (Rabi splitting energy Ω: 1.05 eV) and BP2T-CN (Ω: 1.25 eV) microcrystals owing to their active microresonators providing effective photonic mode confinement. We find that the strength of the coupling between excitons and photons is correlated with the refractive index and absorption coefficient originating from the transition dipole moment and oscillator strength. For BP2T-CN, a larger value of Ω was achieved because of a higher absorption coefficient, larger refractive index, and smaller mode volume.

Time-resolved terahertz (THz) spectroscopy is applied for a microcrystalline film of methylammonium lead bromide perovskite, CH3NH3PbBr3, to observe the carrier dynamics around the band edge. The ultrafast response of the transmitted THz electric field amplitude after carrier generation is modeled with a biexponential curve with ∼5 and 180 ps time constants, which are ascribed to Auger and electron-hole recombination processes, respectively. From the pump photon energy dependence of the time evolution of the THz electric field amplitude, it is shown that the bound exciton states and free interband excited carrier states show a clearly different temporal response. These measurements support the idea that the bound excitons generated in CH3NH3PbBr3 remain as stable excitons even at room temperature (RT). This is in clear contrast to the cases in CH3NH3PbI3 in which the excitons and band-edge free carriers are interchangeable at RT.

Methylammonium lead bromide (CH3NH3PbBr3)/poly(ethylene oxide) (PEO) composites are fabricated by a simple microcapillary method. The addition of PEO into a precursor solution of CH3NH3PbBr3 improv...

Herein, a core–shell heterostructure of H2O-oxidized ZnO nanorod (NR)@Mg-doped ZnO (MZO) nanoparticles (NP) with superior charge transfer capabilities is presented for the first time. ZnO NRs were strategically designed using a low-temperature and sustainable H2O oxidation technique and followed by low-temperature annealing of a spin-coated MZO precursor to form a core–shell heterostructure. Surface morphological and nanobeam electron diffraction (NBD) analysis validated the high-quality crystalline nature of the core–shell heterostructure. The verification of Mg dopant inclusion in the ZnO lattice and uniform distribution were established from X-ray (XRD, XPS, EDX), Raman and electron energy-loss (EELS) spectroscopy analyses. The ZnO NR@MZO NP core–shell film preserved the excellent transparency of the original ZnO NRs and displayed the highest conductivity due to the increased carrier concentration in the MZO shell. Steady-state photoluminescence (PL) intensity of the perovskite film on top of the ZnO NR@MZO NP core–shell film showed the strongest quenching among the samples indicating the fastest electron transfer. This ZnO NR@MZO NP core–shell heterostructure could provide a more efficient transmission channel by supplying a larger electronic contact with the light absorber layer and a direct path for electron transport to the cathode. Ultimately, our results highlight the great potential of the ZnO NR@MZO NP core–shell structure as an electrode not only for photovoltaics but also in other future flexible optoelectronic devices.

Organic semiconductors are promising candidates as platforms for room temperature polaritonic devices. An issue for practical implementation of organic polariton devices is the lowering of condensation threshold. Here we investigate anisotropic light-matter coupling characteristics in an organic crystal microcavity showing strong molecular orientation. Furthermore, the below-threshold excitation dynamics are investigated to clarify the spontaneous transition pathways from reservoir to polariton states. Time-resolved photoluminescence measurements reveal that photonic/excitonic hybrid transition processes coexist in the microcavity system. This finding provides valuable insights into a detailed understanding of polariton dynamics and help in the design of polaritonic devices showing a low-threshold condensed phase.

Developing a consistent and sustainable protocol for fabricating predetermined ZnO nanostructures is of significant interest in materials science and industry, owing to the emergence of ZnO-based devices and applications. Herein, the design of novel nanostructured ZnO films via a green, sustainable and low-temperature H2O oxidation technique is presented. Surface engineering was achieved by controlling the pH value of H2O during oxidation of Zn thin films. Diverse ZnO nanostructures of high structural and optical qualities including nanoparticles, microparticles composed of smaller rods, columnar nanorods and nanotubes having different growth orientations emerged. The morphology, chemical composition, structure, surface chemistry and optical properties of the nanomaterials were comprehensively characterized as a function of pH value. The experimental results and proposed growth mechanism for each nanostructure were presented and thoroughly discussed to have a deeper understanding on the physical insights governing the pH-controlled development of the nanostructures. This in-depth examination could pave the way to pioneering properties and functionalities that could sustainably fulfill the requirements of next generation optoelectronic devices.

Herein, the simultaneous etching and Al doping of H2O-oxidized ZnO nanorods (NRs) to generate Al-doped ZnO nanotubes (AZO NTs) is demonstrated. The innovative approach involves a facile one-step spin-coating of AlCl3 solution on top of the NRs. The polar (001) planes of ZnO were selectively etched due to the acidic nature of the AlCl3 solution, resulting in the transformation of NRs to NTs. At the same time, effective Al doping into the NTs was accomplished. Surface morphological analysis revealed gradual formation of NTs through additional AlCl3 coatings. Evidence of Al dopant inclusion and uniform distribution within NTs was established from XPS, XRD, Raman and EELS elemental mapping analyses. The HRTEM image and SAED pattern showed that the AZO NTs have a high-quality crystalline structure. Higher transmittance and a blue shift in absorption edge can also be observed in doped films indicating band gap broadening. A new green emission in the PL spectra of AZO NTs emerged due to the formation of oxygen vacancies. Most importantly, the AZO NTs showed higher electrical conductivity and electron mobility values compared with undoped ZnO NRs. Steady-state PL spectra of perovskite films on top of AZO films were quenched stronger than those of ZnO NRs, indicating faster electron transfer in the perovskite/AZO NTs interface. These results highlight the potential of AZO NTs as an electrode for solar cells and other optoelectronic devices. Ultimately, our approach offers an attractive strategy to enhance the charge-transport properties of nanostructured materials.

Simulations on Bloch surface waves and Bloch surface wave–exciton–polaritons based on the transfer matrix method were performed using only the layer thicknesses and refractive indices of the materials. We demonstrate that the incorporation of the influence of active layer is necessary to accurately determine the Bloch surface wave dispersion. Furthermore, the mode splitting that gives rise to the lower and upper polariton branches can be simulated by including the full dispersive refractive index of the active layer in the transfer matrix calculation. We show the dependence of coupling strength on active layer and truncation layer thicknesses, which implies that the Bloch surface wave–exciton interaction strength can be tuned just by changing these structural parameters. Furthermore, we calculate the area inside the dips corresponding to the lower and upper polariton modes, which can serve as an indicator of mode visibility. We find that in the Kretschmann–Raether configuration, a tradeoff between high Rabi splitting and good mode visibility must be taken into account in designing multilayer structures for Bloch surface wave–exciton–polaritons. Angle-resolved reflectivity maps were also calculated to illustrate how these results can be observed in an experimental set-up. This work serves as a guide map in the design and potential optimization of multilayer structures for the study of two-dimensional polaritonic systems.

As new candidates of thiophene/phenylene co-oligomer (TPCO) species, 5,5′′-bis(4′-methoxy-[1,1′-biphenyl]-4-yl)-2,2′:5′,2′′-terthiophene (BP3T-OMe) and 4′,4′′′-([2,2′:5′,2′′-terthiophene]-5,5′′-diyl)bis(([1,1′-biphenyl]-4-carbonitrile)) (BP3T-CN) were synthesized for lasing applications. Although most unsubstituted TPCO species crystallize in monoclinic form, BP3T-OMe and BP3T-CN crystallized in orthorhombic and triclinic forms, respectively. Since the unsubstituted species, 5,5′′-bis(4-biphenylyl)-2,2′:5′,2′′-terthiophene (BP3T), shows unique and superior lasing performance in single crystals, the newly synthesized BP3T-OMe and BP3T-CN have possibilities to show different or improved optoelectronic characteristics. Amplified spontaneous emission (ASE) and optically pumped lasing were observed from both of the single crystals based on their well-shaped crystalline cavity and high group refractive index values of 3.7–5.3 for excellent light confinement. The lasing threshold for the BP3T-OMe crystal was lower than that for the BP3T-CN crystal, which was attributed to their different molecular orientation, standing in the former and inclining in the latter.

An efficient synthesis for 1-(pyridin-2-yl)-3-(quinolin-2-yl)imidazo[1,5-a]quinoline (PCIC) is presented. Molecular properties as well as thin film deposition and characterization are reported. With an ionization energy of 5.5 eV estimated from cyclic voltammetry and a quantum yield of 28% as determined in solution, the molecule proved promising as possible component of light emitting devices. Therefore, studies in the solid state of PCIC were conducted. Thin films of PCIC were obtained by physical vapor deposition whose morphology was analyzed by atomic force microscopy. Crystals of the molecule were grown by recrystallization from solution or by entrainer sublimation. The structure of crystals depending on preparation route was analyzed by XRD and the results were used to discuss the structure in thin films. Photoluminescence characteristics were investigated in detail for the crystal needles and the vapor-deposited thin films, showing a dependence of emission maximum and the fine structure of bands on the molecular packing. The desired blue emission was measured even at air which is promising for technical application of the material and proves its stability against oxidation.

Electron transport is one of the most crucial processes that determine charge collection efficiency in perovskite solar cells. Herein, a low temperature-processed ZnO-TiO2 nanocomposite is developed as an electron transporting layer for perovskite solar cells. Highly-crystalline ZnO nanorods were deposited electrochemically which served as the scaffold for spin-coated TiO2 nanoparticles. This ZnO-TiO2 nanocomposite is designed to integrate the fast electron transport along the nanorods and the additional surface area provided by the nanoparticles for enhanced electronic contact between the electron-transporting layer and the perovskite layer. A weak photoluminescence quenching behavior was observed for ZnO nanorods after TiO2 nanoparticle coating which signifies a reduction in ZnO surface defects. Steady-state photoluminescence and optical absorption measurements indicated improved charge transfer and higher absorption of light, respectively, when ZnO-TiO2 nanocomposite is contacted with the CH3NH3PbI3 layer. However, the clustering of the nanoparticles caused inefficient charge transfer from TiO2 to ZnO.

Influence of onion-like carbon (OLC) thin films as insertion layer on the photovoltaic characteristics of soluble zinc phthalocyanine (zinc 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (ZnPc-TB))-based solar cells is investigated. Atmospheric photoelectron yield spectroscopy and ultraviolet-visible absorption spectroscopy reveal that the ionization potential and optical bandgap are 4.84 and 1.70 eV, respectively, for ZnPc-TB and 5.23 and 2.02 eV, respectively, for OLC. The power conversion efficiency of the OLC-inserted solar cell was higher than that of a cell without the OLC interlayer by a factor of 5.3. Improvement in photovoltaic parameters and photocurrent is attributed to an increase in the shunt resistance by a factor of 5.5 due to the OLC thin film which functions as a hole collection layer. The OLC-inserted bulk-heterojunction solar cells comprising ZnPc-TB and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) achieve the best performance with the power conversion efficiency up to 6.9 × 10−2% owing to an enhanced contribution of ZnPc-TB to a photocurrent generation. The OLC thin films acting as the hole collection layer provide a new alternative for solution-processed organic solar cells.

Microcavity systems with organic luminescent materials have a hot prospect for room-temperature cavity-polariton devices. The polariton dispersion relation of organic microcavities is significantly different from that of inorganic microcavities due to the strong localization of Frenkel excitons. Also photoexcited particles will undergo a different cooling mechanism until they reach the polariton ground state. In the characterization of efficient polariton condensates, therefore, the polariton cooling dynamics as well as the kinetics of the polariton eigenstate should be measured. Here we present experimental studies on ultrafast dynamics of cavity polaritons in an organic single-crystal microcavity under nonresonant pumping. In time-resolved photoluminescence measurements we observed, for the first time, an ultrafast dynamics of stimulated cooling of the organic cavity polariton. Transient transmission measurement enabled us to investigate the detailed renormalization dynamics of the polariton eigenstate....

Improved photovoltaic performance of perovskite solar cells is demonstrated through the synergistic effect of electrodeposited ZnO nanorods and rubrene:P3HT bilayer as electron and hole-transporting layers, respectively. Highly crystalline ZnO nanorods were obtained by electrochemical deposition in a chloride medium. Additionally, rubrene interlayer was able to passivate or cover the grain boundaries of perovskite film effectively that led to reduced leakage current. A perovskite solar cell optimized with ZnO nanorods and rubrene:P3HT bilayer achieved a maximum efficiency of 4.9% showing reduced hysteresis behavior compared with the device having P3HT as the only hole-transporting layer. The application of longer nanorods led to better perovskite infiltration and shorter charge carrier path length. These results highlight the potential of electrodeposited ZnO nanorods and rubrene:P3HT bilayer as charge selective layers for efficient perovskite solar cells.

Micro-ring structures with methylammonium lead bromide (CH3NH3PbBr3)/poly(ethylene oxide) (PEO) composites are fabricated by using a microcapillary as a template. By the fast-drying process, the CH3NH3PbBr3/PEO composite films with a high PEO concentration are deposited to homogeneously cover the inner surface of the microcapillaries. Under optical pumping, whispering gallery mode lasing is observed from the inner circumference of microcapillaries, which works as a micro-ring cavity. With a reduction in ϕ, the mode number and lasing threshold fluence decrease, suggesting that the stimulated emission is enhanced based on cavity quantum electrodynamics in the CH3NH3PbBr3/PEO composite films uniformly covering the inside of microcavities.

Molecular nanowires are one of potential materials towards realizing electrically pumped organic lasers. Strong light confinement in the one-dimensional cavity results in axial Fabry-Perot lasing at a low threshold of excitation fluence. In particular, the molecular orientation, i.e. anisotropic transition dipole moment, plays an important role to enhance the stimulated emission process along the nanowire axis. From this point of view, here we prepared epitaxially grown nanowires of semiconducting thiophene/phenylene co-oligomers (TPCOs) by mask-shadowing deposition on a cleaved (001) surface of a potassium chloride (KCl) crystal. Under optical pumping, single nanowires of both unsubstituted (p-type) and cyano-substituted (n-type) TPCOs exhibited multimode F-P lasing above a threshold fluence of >10 uJ/cm2 which decreased with increasing nanowire lengths. Their lying molecular orientation and stacking along the nanowire axis in both TPCOs are suitable for effective light propagation with transverse-electric mode resulting in better lasing performances compared to two-dimensional platelet crystals of TPCOs.

We investigated the formation of single-crystal CH 3 NH 3 PbCl 3 and CH 3 NH 3 PbI 3 perovskites by cast-capping method. This very simple but high efficiency technique based on modified solution process was successful to grow large-domain single crystals up to a millimeter size. Their X-ray diffraction patterns revealed that both crystals grew in the cubic form. The (100) planes of both crystals grew predominantly in contact with the substrate surface. The present technique helps further studies as an alternative method to fabricate high performance functional devices.

A cyno-substituted thiophene/phenylene co-oligomer (TPCO), 5,5′-bis(4′-cyanobiphenyl-4-yl)−2,2′-bithiophene (BP2T-CN), is vapor-deposited on KCl (001) surface kept at 220 °C by the mask-shadowing method. Transmission electron microscopy and fluorescence microscopy reveal that the deposited BP2T-CN crystallizes in two types of morphologies: microneedles and thin film crystallites. In particular, the predominant microneedles epitaxially grow in four directions in the manner that the BP2T-CN molecules align along the [110] KCl or [−110] KCl . X-ray diffraction patterns indicate that the BP2T-CN molecules in the microneedle lie parallel while those in the thin film crystallite obliquely stand on the KCl surface.

We propose a crystalline film growth technique for organic materials called vaporized film deposition (VFD). This method consists of two simple step: vapor-depositing a microcrystalline film on a substrate, then transferring it on another substrate by heating in vacuum. In this study, we used a cyano-substituted π-conjugated oligomer, 5,5’-bis(4’-cyanobiphenyl-4-yl)-2,2’-bithiophene (BP2T-CN). By placing the two substrates with a spacing of

A strategic low temperature oxidation of Zn thin films in water is presented to fabricate nanostructured ZnO as an electron transporting layer in efficient solid-state perovskite solar cells (glass/ITO/ZnO/perovskite/P3HT/Ag) for the first time. By controlling the oxidation time and temperature, novel nanostructured surface morphologies including platelets, rods, honeycomb structures and fibrous wires composed of particles are obtained. Nanostructures formed in longer reaction times show reduced concentration of surface defects improving the possible recombination losses in solar cells. The perovskite solar cell based on room temperature oxidized fibrous ZnO nanostructures exhibited a respectable maximum efficiency of 3.62%. This efficiency is improved up to 5.96% by utilizing the pointed nanorod morphology generated by oxidation at a growth temperature of 90 °C for 8 h. Most of the fabricated solar cells based on rod-like structures show higher efficiencies, weaker hysteresis behavior and good stability owing to the enhanced electronic properties and interfacial area between ZnO and the active layer. These results highlight the potential of wet oxidized nanostructured ZnO as an electron selective layer for low cost, sustainable and large-scale production of flexible perovskite solar cells.

Organic electroluminescence (EL) devices with surface-emitting microcavity structure were fabricated using vapor-deposited films of thiophene/phenylene co-oligomer derivatives, aiming at polariton formation under electrical excitation. Owing to strong coupling between excitons and photons in the device, we demonstrated the formation of cavity polaritons with a large Rabi-splitting energy (2ħΩ = 250 meV). Furthermore, efficient relaxation into the bottom of lower polariton branch was confirmed from angle-resolved EL spectra. In excitation-density dependence, the luminance of microcavity EL devices showed a superlinear increase with an elevation of current density indicating a contribution of triplet excitons.

Enhancing the magneto-optical (MO) response of magnetic films and nanostructures is an important issue for a wide variety of applications, including biosensing. Past success via multilayer stacking has been focused primarily on symmetric or periodic geometries. Here, however, the authors find that a quasiperiodic structure exhibits a far larger MO response than a similar periodic structure, over a broad spectral range, even though both samples have otherwise very similar magnetic and optical properties. Model calculations based on local optical properties fail to describe this behavior; more fundamental, nonlocal effects must be the origin of the massively enhanced MO signal.

Organic molecular crystals have a variety of low frequency vibrational modes composed of intra- and inter-molecular oscillations. They are mixed intricately in the terahertz (THz) region. We are interested in the controllability of the vibrational energy distribution among such THz vibrational modes based on the femtosecond double-pulse excitation scheme. Single crystalline rubrene is prepared by physical vapor transport. The optical response of vibrational modes in the electric ground state of rubrene is detected by the ultrafast pump-probe reflectivity measurement at 90 K. Three oscillation modes at 3.20, 3.67, and 4.18 THz are detected, and we demonstrate selective enhancement and depletion of each mode by properly tuning the double-pulse delay. The amplitude of the selected vibrational mode is modulated between 0.149 and 1.87, where 1.0 corresponds to the amplitude excited with a single pump pulse. The double-pulse delay dependence of the observed vibrational amplitude is simulated based on the classical driven harmonic oscillator model, and the results reasonably reproduce our experimental signals. Such selective manipulation of the vibrational amplitude can be a potential tool to investigate the vibronic and electron-phonon couplings which plays an important role for the charge transport characteristics and various optoelectronic properties in organic molecular crystals.

Distributed feedback (DFB) lasing is achieved with CH3NH3PbBr3 perovskite embedded in channel-type waveguides. By using a focused ion beam, DFB gratings are engraved within the bottom surface of channel-type waveguides etched on a SiO2/Si wafer. The oriented CH3NH3PbBr3 crystallized inside the waveguide with the DFB gratings shows second-order DFB lasing mode in lateral and normal directions above a threshold excitation density of 47 μJ cm−2 which is one order of magnitude lower than that in the non-DFB laser. The splitting DFB peaks are well reproduced by finite-differential time-domain calculation. The peaks change to a power-broadened amplified spontaneous emission as the excitation fluence is increased far above the threshold.

Silver mirror planar microcavity containing dye J–aggregates is fabricated by a vacuum deposition method. Characterization of the microcavity with the dye J–aggregates of lower concentration (7.70×10 −4 M) in comparison with the previous studies is performed. Optical strong coupling between excitons and confined photons within the microcavity is demonstrated from the anticrossing of exciton and photon modes. Angle-resolved transmission measurements give a Rabi-splitting energy of ~190 meV for the upper and lower polariton splitting. The fabrication of such a simple metal–mirror–based microcavity ( Q –factor ~13) leads to a progress of polaritonic characterization of organic media.

Hybrid solar cells were fabricated using aluminum-doped zinc oxide (AZO) grown by electrochemical deposition from chloride electrolyte solutions with Al/Zn molar ratios of 0.5, 2.5, and 5.0%. The substrates were AZO- and ZnO-seeded ITO. Ordered nanorod structures with high optical transmittance were grown at 0.5% Al/Zn ratio while interconnected micron-sized flakes were grown at 2.5% and 5.0%. The estimated band gap energies increase for higher Al dopant content, showing Burstein-Moss effect. EDX analysis detected high aluminum content in the 5.0% samples suggesting that insulating aluminum oxide phases were formed thus causing reduced solar cell efficiencies. The highest power conversion efficiency of 1.71%, from the 0.5% sample grown on ZnO-seeded ITO, can be attributed to the presence of AZO nanorods which provide a large interfacial area and effective charge transport.

Organic light-emitting diodes with trilayer PIN structures are fabricated using only thiophene/penylene co-oligomer derivatives: 5,5'-bis(4-biphenylyl)-2,2'-bithiophene (BP2T), 5'''-bis(4-trifluoromethylphenyl)[2,2';5',2'';5'',2''']quaterthiophene (P4T-CF3), and 5,5'-bis-(4'-cyanobiphenyl-4-yl)-2,2'-bithiophene (BP2T-CN) as the P, I, and N materials, respectively. As designed from their expected frontier orbital energies, electroluminescence (EL) is obtained from the P4T-CF3 layer. When the BP2T layer is first deposited on an indium-tin-oxide (ITO) substrate, the device (Al:Li/BP2T-CN/P4T-CF3/BP2T/ITO) shows homogeneous EL. On the other hand, the device with an opposite deposition order (Au/BP2T/P4T-CF3/BP2T-CN/ITO) shows dotted EL with higher efficiency at lower bias voltages. By decreasing the deposition rate of the P4T-CF3 layer in the latter device, its morphological change results in homogeneous EL with increased density of dotted emission.

Herein, the accelerated growth of nanostructured ZnO films via a facile, sustainable and low-temperature microwave-assisted H2O oxidation is presented for the first time. This novel technique involves the oxidation of Zn thin films in pure H2O under microwave irradiation to form nanostructured ZnO films. ZnO nanorods (NRs) were readily obtained after 30 min of microwave irradiation without the presence of any catalysts, surfactant or ligands. Moreover, increasing the irradiation time led to the conversion of NRs to honeycomb-like structures composed of nanotubes (NTs). The high-quality crystalline nature of the nanostructured ZnO films was established from XRD, Raman and HRTEM analyses. Based on XPS analysis, the duration of irradiation time controlled the amount of OH– group on the surface of the ZnO films. Insignificant amount of oxygen vacancies and OH– group were found for the films obtained at longer irradiation time. Most notably, the ZnO film with honeycomb-like structure formed after 2 h of irradiation exhibited the most promising electron-transporting capability based on steady-state PL analysis. These results highlight the potential of H2O-oxidized nanostructured ZnO films as electrode for photovoltaic devices. Finally, this study offers a promising approach which could sustain the requirements of future ZnO-based optoelectronic devices.

We report on the fabrication and characterization of low-dimensional single crystals of hexyl-substituted thiophene/phenylene co-oligomer, 5,5'-Bis(4'-n-hexyl-4-biphenylyl)-2,2'-bithiophene (BP2T-Hx). X-ray diffraction measurements of the single crystals reveal that BP2T-Hx molecules crystallize in a monoclinic form. Temperature dependence of photoluminescence (PL) decay profiles of the BP2T-Hx crystal results in a PL quantum yield of 39%. Above an excitation threshold of 262 μJ/cm2, amplified spontaneous emission is obtained in a disk-shaped crystal of BP2T-Hx based on the self-waveguiding effect of fluorescence light. Owing to two-dimensional light confinement supported by high group refractive index of 3.4 and high quality factor of 3800, the one-dimensional needle crystal with a cavity length of 70 μm realizes a Fabry-Pérot lasing at a threshold of 186 μJ/cm2 which is 29% lower than that of the disk-shaped crystal.

Herein, we present a vapor film deposition method for fabricating polycrystalline films of a thiophene/phenylene co-oligomer. The polycrystalline film has comparable physical and optical characteristics, e.g. an amplified spontaneous emission, to those of the single-crystal phase as the film consists of tiny single crystals with a grain size of 5–20 μm. Meanwhile, in situ FET results illustrate the dominant unipolar p-type characteristics with a hole mobility of 0.025 cm2 V−1 s−1, higher than the conventional physically deposited films owing to the standing molecular orientation.

We report LED properties in perovskite semiconductors and thiophene/phenylene co-oligomers (TPCOs) double heterostructures. Perovskite semiconductors have been formed by using the simple solution-process, "cast-capping method" on the substrates with TPCOs. The electroluminescence has quenched rapidly, but it has recovered to nearly initial states. Under the pulsed operation within 3 V, the device has rather long durability. We have compared LED properties with those of the TPCO LEDs. The ion migrations and/or light-emitting electrochemical cell operations are strongly suggested in the perovskite/TPCO LEDs.

Microneedle crystals of 1,4-bis-(4-methylstyryl)benzene (DSB-4Me) and amorphous microdots of bis (N,N-di-p-tolylamino-p-styryl)benzene (DADSB) are fabricated by using mask-shadowing and conventional vapor deposition techniques. By interaction between π-conjugated electronic chains and ionic lattice of a KCl crystal substrate, DSB-4Me molecules grow into needle crystals epitaxially orienting in four directions making ±60 against [110]KCl and [-110]KCl. As for DADSB, self-assembly into microdots by heating the KCl substrate at 180C during deposition is attributed to the impact of bulky peripheral groups in DADSB and surface migration of the deposited molecules. Moreover, while amplified spontaneous emission (ASE) is observed above an excitation threshold of 362 μJ/cm2 in the DSB-4Me microneedle crystals, a lower threshold whispering-gallery mode (WGM) lasing is observed above 37 μJ/cm2 for DADSB microdots owing to the higher waveguide quality.

We investigate the microwave spectroscopies of a micrometer-sized single permalloy (Py) chiral structure on coplanar waveguides (CPWs). Under an external dc magnetic field applied in a direction perpendicular to the microwave propagation, the Py chiral structure loaded on the center of the CPW signal line shows Kittel-mode ferromagnetic resonance. Contrastingly, the structure on the signal-line edge highlights two additional resonances: spin-wave resonance at a higher frequency, and unique resonance at a lower frequency of approximately 7.8 GHz. The resonance signal at 7.8 GHz originates from magnetically induced, geometry-driven resonance, although the resonance frequency does not depend on the external magnetic field. Moreover, the displacement of the Py structures on the signal line results in nonreciprocal microwave transmission, which is traced back to the edge-guide mode.

Herein we experimentally study magnetic multilayer metamaterials with broken translational symmetry. Epitaxially-grown iron-gold (Fe-Au) multilayers modulated using Fibonacci sequence—referred to as magnetic inverse Fibonacci-modulated multilayers (IFMs)—are prepared using ultra-high-vacuum vapor deposition. Experimental results of in-situ reflection high-energy electron diffraction, magnetization curves, and ferromagnetic resonance demonstrate that the epitaxially-grown Fe-Au IFMs have quasi-isotropic magnetization, in contrast to the in-plane magnetization easy axis in the periodic multilayers.

A novel series of alkyl-monosubstituted thiophene/phenylene co-oligomers (TPCOs) has been synthesized and characterized. The introduction of alkyl chains to TPCOs improved the solubility in organic solvents. Thin films of these compounds were prepared by the vacuum-deposition, solution-cast, and skim methods. Of these, the solution-cast films and skim films consist of highly-ordered structures characterized by molecular bilayers. In particular, the skim method produced a large-sized free-standing thin film. We investigated the carrier transport of the thin films on the field-effect transistor (FET) configurations. These FET devices exhibited typical p-channel characteristics with clear saturation region. The introduction of alkyl monosubstituents is responsible for enhancement in the carrier mobility. The device characteristics are contrasted with those of alkyl-disubstituted compounds.

align almost perpendicular to the crystal face. [ 10,11 ] Since the π-electronic transition dipole between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively) is parallel to the molecular axis, those monoclinic crystals result in low-threshold lasing due to the effective stimulated emission with the transverse magnetic (TM) mode. [ 12 ] By introducing methoxy groups at the molecular terminal of BP1T, 2,5-bis(4′-methoxybiphenyl-4-yl)thiophene (BP1T-OMe) changes to crystallize in an orthorhombic form in which all molecules perfectly stand upright to the crystal face. [ 13 ] This upright orientation is the most favorable for the TM-mode lasing in the platelet crystal. Besides such crystallographic modifi cation, the substituents into the TPCO molecule also change the p/n conduction types. Introduction of electron-withdrawing groups at the molecular terminal increases an electron-accepting nature resulting from lowered π electronic energies. Yamao et al. have confi rmed the n-type conduction from a light-emitting FET device with vaporgrown crystals of 1,4-bis{5-[4-(trifl uoromethyl)phenyl]thiophen2-yl}benzene (AC5-CF 3 ). [ 14 ] By introducing trifl uoromethyl groups, the HOMO/LUMO energies of AC5-CF 3 are deepened by 0.35 and 0.41 eV, respectively, in comparison to those of unsubstituted AC5 as demonstrated by the density functional theory (DFT) calculations. [ 15 ] In this study, we chose substitution into BP1T with cyano groups which are stronger electronwithdrawing than trifl uoromethyl groups. [ 16,17 ] The HOMO and LUMO energy levels of 2,5-bis(4’-cyanobiphenyl-4-yl)thiophene (BP1T-CN) [ 4 ] are deepened by 0.48 and 0.65 eV, respectively with respect to those of unsubstituted BP1T (Figure S1). In contrast to the elevation of HOMO and LUMO energies by 0.20 and 0.19 eV, respectively, for the p-type BP1T-OMe, stronger n-type conduction is expected for BP1T-CN. While optically pumped lasing has been extensively investigated for p-type TPCO crystals, [ 18,19 ] there is no report for those n-type TPCOs so far. Here we investigated the optically pumped lasing from single crystals of a new derivative of BP1T-CN. First, we characterized a crystal structure of BP1T-CN grown from a vapor phase. A fl uorescence micrograph of a representative BP1T-CN crystal is shown in Figure 1 (a). The crystal is bluegreen-emitting with a fl uorescence maximum at λ = 500 nm under ultraviolet (UV) excitation (Figure S2). As compared to fl uorescence images of typical p-type TPCO crystals (Figure S3), remarkable differences appear in the BP1T-CN crystal: the crystal shape is typically rod-like instead of thin plate-like. The emission is enhanced at the both ends of the rod instead at all edges of the thin plate. The fl uorescence is radiated also from the top face of the rod crystal (Figure 1 (a)) whereas no fl uorescence is seen in Optically Pumped Lasing from Single Crystals of a CyanoSubstituted Thiophene/Phenylene Co-Oligomer

Zinc oxide (ZnO) nanostructures with various morphologies (pencil-like nanorods, nanotubes, and lotus-like structures) have been successfully formed by simple oxidation of vacuum deposited Zn thin film on glass/ITO substrates in hot water at 90 °C. The morphology evolved from pencil-like nanorods to nanotubes to lotus-like structures with prolonged oxidation of Zn thin film for 6–24 h. The change in morphology of ZnO is attributed to the combined effects of electrochemical reactions in the solution, morphology and structure of Zn thin film, and wurtzite structure of resulting ZnO. A hybrid organic–inorganic solar cell following an inverted bulk heterojunction configuration was fabricated based on the lotus-like ZnO structures. The solar cell achieved a power conversion efficiency of up to 1.18%, which demonstrates the applicability of the technique for photovoltaic applications.

Organic semiconductor microcavities forming strongly coupled exciton-polaritons are interesting systems due to their nonlinear coherent emission observed even at room temperature. Here, we investigate the incident angle and photon-energy-dependent photoemission from a planar organic microcavity to evaluate the relaxation efficiency towards the bottom of the lower polariton branch. We observe nonlinear increase in the vertical emission from the microcavity when the sample is pumped resonantly to the lower polariton branch with an incident angle of 30 to 55°. The observed results support the fast and efficient relaxation of organic microcavity polaritons within the lower polariton branch.

Optically pumped lasing is observed in cyano-substituted thiophene/phenylene co-oligomer (TPCO) microcrystals fabricated by the slide boat method. Dot-shaped crystals approximately 10 μ m in size are obtained. Needle- and platelet-like crystals are also obtained in other TPCO derivatives. The needle and platelet crystals show a lower lasing threshold than that of the dot-shaped crystals with clear multimode lasing spectra. A brief discussion follows on how to improve film fabrication from microdot and platelet crystals to film-like morphology.

We have grown crystals in which two kinds of thiophene/phenylene co-oligomers (TPCOs) are hybridized. Biphenyl-capped thiophene (BP1T) and biphenyl-capped terthiophene (BP3T) were chosen from among the TPCOs. The hybrid crystals were grown in both the vapor phase and the liquid phase. These hybrid crystals showed the emission colors intermediate between the two components. Correspondingly maximum peak positions of the emissions from the hybrid crystals were located halfway between those from single-component crystals of BP1T and BP3T. We made hybrid thin films by co-deposition of the two TPCOs in vacuum. The thin films exhibited both emission colors and emission peak positions similar to those of the hybrid crystals. The X-ray diffraction measurements indicate that the crystallographic structure of the hybrid crystals resembles that of the BP1T crystal. Also we made field-effect transistors using the hybrid crystals and measured their hole mobilities. We briefly discuss the implications of the X-ray diffraction and electrical data.

Photoluminescence from an organic microcavity is investigated using vapor-grown single crystals of 5,5'-bis(4'-cyano-biphenyl-4-yl)-2,2'-bithiophene (BP2T-CN). A vertical half-cavity structure is fabricated with thin platelet crystals of BP2T-CN placed on a distributed Bragg reflector (DBR). Lying orientation of the BP2T-CN molecules is suitable for effective surface emission from the cavity. Angle-resolved photoluminescence spectra show anticrossing splits, suggesting the formation of cavity polaritons induced by coupling between confined photons and excitons. Phenomenological analysis well reproduces the dispersion characteristics with a Rabi splitting energy of 90 meV at room temperature. With increasing excitation fluence under optical pumping, one of the cavity photon modes is gain-narrowed, and amplified emission is obtained from the surface-emitting half-cavity structure.

We investigate the ferromagnetic resonance (FMR) of a single chiral structure of a ferromagnetic metal—the magnetochiral (MCh) metamolecule. Using a strain-driven self-coiling technique, micrometer-sized MCh metamolecules of metallic permalloy (Py) are fabricated without any residual Py films. The magnetization curves of ten Py MCh metamolecules obtained by an alternating gradient magnetometer show soft magnetic behavior. In cavity FMR with a magnetic-field sweep and coplanar-waveguide (CPW) FMR with a frequency sweep, the Kittel-mode FMR of the single Py metamolecule is observed. The CPW-FMR results, which are consistent with the cavity-FMR results, bring about the effective g factor, effective magnetization, and Gilbert damping of the single metamolecule. Together with calculations using these parameters, the angle-resolved cavity FMR reveals that the magnetization in the Py MCh metamolecule is most likely to be the hollow-bar type of configuration when the external magnetic field is applied parallel to the chiral axis, although the expected magnetization state at remanence is the corkscrew type of configuration.