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Solubility enhancement is a key issue for developing the perylene diimide‐based functional materials. Introduction of curved structure proved an effective solubilizing method without employing steric repulsion. In this work, wavily curved perylene diimides were developed as a new family of highly soluble curved perylene diimides. Moreover, their conformational dynamics, aggregating properties, electronic properties, and photovoltaic performances were thoroughly examined in comparison to the previously reported isomer exhibiting an arched curvature. The waved isomer demonstrated heightened rigidity and a greater propensity for aggregation compared to the arched isomer, likely attributed to its more planar structure. Each benzoxepin unit played a role in cancelling out the curvature on the opposite side. While the difference in the molecular curvature did not cause significant alterations in the photophysical and electron‐accepting properties, we identified that the modulation of the curved structure is effective in controlling the morphology of the photoelectric conversion layer. [ABSTRACT FROM AUTHOR]

Doping effects on organic lateral photovoltaic cells with separated carrier‐generating and doped carrier‐transporting layers are investigated. A doping concentration of 100 ppm into the lateral hole and electron transporting layers doubles the photocurrent density by forming a built‐in potential between the layers in the vertical direction of the lateral cell, which accelerates carrier generation. A higher doping concentration induces trap‐assisted recombination at direct C8‐BTBT/PTCDI‐C8 contact points and causes a decrease in photocurrent density. [ABSTRACT FROM AUTHOR]

We have elucidated the details of the photodegradation of non‐fluorinated benzoindolenine‐based SQ dyes with low photostability in solution and proposed a hypothesis to improve their photostability. Based on the results, replacing all the hydrogen atoms on the benzoindolenine ring with fluorine atoms or methylation of the oxygen anions of the non‐fluorinated benzoindolenine SQ dye resulted in improvement of photostability. Furthermore, a preliminary investigation of the synthesized SQ dyes for organic photovoltaics revealed that the O‐methylated SQ dye with bulky fluorine‐containing anions provided a much higher Voc than similar benzoindolenine‐based SQ dyes. [ABSTRACT FROM AUTHOR]

A remaining frontier in the field of organic light‐emitting diodes (OLEDs) is reducing their operating voltage. Herein, an efficient OLED is reported, operable by a 1.5 V battery, that produces bright emission equivalent to the luminance of a typical display. The OLED has a smaller turn‐on voltage at 0.97 V than an optical energy of emitted photons at 2.04 eV (608 nm), because the OLED is based on an upconversion (UC) transition associated with triplet–triplet annihilation that doubles the energy of excited states. The characteristics of charge transfer (CT) state at the interface have been revealed, which are key to efficient UC, and the percentage of excited states deactivated by parasitic loss processes during the UC transition is significantly reduced from over 90% to approximately 10% by introducing a highly crystalline acceptor material and an emissive dopant. Consequently, the UC‐OLED achieves a quantum efficiency that is two orders of magnitude higher than that in the previous report. [ABSTRACT FROM AUTHOR]

Hydrogen (H2) is increasingly employed in industrial applications, such as developing hydrogen fuel cells for vehicles and power plants. However, H2 explodes at a concentration limit of 4%, necessitating the development of ultrasensitive hydrogen sensors capable of early‐stage detection of hydrogen leaks. In this study, nano‐patterned polycrystalline cupric oxide (CuO) nanowire array nanogap gas sensors with voids are fabricated using electron‐beam lithography and ex situ oxidization by annealing, which could detect 5 ppb H2 and show response and recovery times of less than 10 s without a baseline shift. Combining a pre‐H2 annealing process in Ar/H2 for Cu nanowires and a low‐rate oxidation process enhances the crystallinity of CuO nanowires, facilitating the preparation of polycrystalline CuO nanowires with voids, which is a significantly practical approach for the improvements of gas sensing properties. Response and recovery times of <10 s can be obtained for a gap separation of ≈30 nm. These improvements are discussed based on a high electric field of ≈1.3 MV cm−1. The relationship between the normalized response and H2 concentration is discussed based on the power law. This paper presents highly reliable and fast H2 sensors without a baseline shift to meet the demands of the hydrogen industry. [ABSTRACT FROM AUTHOR]

The influence of N‐substituents on the photovoltaic properties of singly bay‐linked perylene diimides (diPDIs) was systematically investigated to understand the aromatic‐aliphatic balance, which is beneficial for achieving high device performance in organic photovoltaic (OPV) systems. The synthesis of various N‐substituted diPDIs was successfully achieved using a newly developed one‐step procedure, resulting in sufficiently high yields. Detailed investigations of seven variants of diPDIs demonstrated that the primary alkyl substituents, particularly the 2‐ethylhexyl group, induce the self‐organized growth of thin films with high crystallinity. This is beneficial for enhancing the device performance of bulk heterojunction (BHJ) systems. The results presented herein reveal the important roles of alkyl side chains as hydrophobic solubilizing auxiliaries or primary determinants in the control of the active layer nanomorphology. This offers a valuable guideline that is essential for developing high‐performance organic semiconductor materials for future practical applications. [ABSTRACT FROM AUTHOR]

Curved perylene diimides fused with seven‐membered rings have been synthesized using a regioselective bay‐functionalization method and Pd‐catalyzed intramolecular C−H/C−Br coupling reaction. X‐Ray analysis and temperature‐dependent NMR spectroscopy revealed the curved molecular structure with a certain degree of conformational flexibility. The curved and expanded π‐conjugation altered the electronic properties while retaining the intrinsic properties of the parent perylene diimide. Despite the absence of solubilizing N‐substituents, the curved perylene diimides showed sufficient solubility for application in solution‐processed organic photovoltaic devices. The devices showed superior performance with a power conversion efficiency of up to 2.76% due to suppressed charge recombination. Our detailed investigations suggest that the introduction of a curved structure enables the removal of the bulky N‐substituents, which is an effective way to achieve a thin‐film morphology suitable for photoelectric conversion. [ABSTRACT FROM AUTHOR]

The development of an efficient synthetic protocol for multiply bay‐functionalized perylenes and application of these products to photovoltaics are reported. Tetrabenzyl 1‐(4‐tert‐butylphenoxy)perylene‐3,4,9,10‐tetracarboxylate underwent a regioselective bromination at the 7‐position followed by a further bromination at the 12‐position to provide a 7,12‐dibromide in high 84% yield. This compound was transformed into a tetrasubstituted C2h‐symmetric dibromide by a controlled monoetherification and a final bromination. The synthetic versatility of the new brominated precursors was demonstrated by their application to cross‐coupling reactions, cyanation, and derivatization to the corresponding perylene diimide (PDI). Owing to the high solubility and the raised LUMO level, the obtained tetrasubstituted PDI showed significant advantages as an acceptor material for photovoltaic applications, exhibiting a remarkably high open‐circuit voltage (VOC) reaching 1.00 V. The observed high VOC could be understood by reduction of energy offset for charge separation and non‐radiative recombination loss. [ABSTRACT FROM AUTHOR]

Reducing the energy loss in output voltage is critically important for further enhancing the efficiency of organic solar cells (OSCs). Here, we report that OSCs with high mobility and highly crystalline donor (D) and acceptor (A) materials were able to reduce an open-circuit voltage (VOC) loss. The crystallinity of the acceptor layer could be altered by appropriate selection of the three molecules with different alkyl side chain lengths. The VOC was found to increase as the crystallinity of the acceptor layer increased. The origin of the high VOC was that the highly crystalline D/A interface reduced the energy loss in the output voltage by realizing ideal band-to-band recombination. Especially, the high crystallinity of the several molecular layers (less than 6 nm) in the vicinity of the D/A interface was important for realizing the high VOC. Our results demonstrate that the careful design of the D/A interface enables high power conversion efficiencies to be achieved in OSCs by reducing open-circuit voltage loss. [ABSTRACT FROM AUTHOR]

Very low activation energy for hole generation reaching 5.7 meV to realize the ionization rate of 100% at room temperature by surface doping of molybdenum oxide on rubrene single crystals was observed from the temperature dependence of the hole concentration directly measured by the Hall effect. Hole mobility having band-conductive nature was maintained after surface doping. Very low activation energy can be explained by the overlap of shielded Coulomb potentials. By increasing the concentration of charge transfer states at the interface between the crystal and the dopant, high doping efficiency can be achieved. [ABSTRACT FROM AUTHOR]

Formation of pn homojunction in a single semiconductor material through doping is key for photocurrent generation in inorganic solar cells (SCs). In contrast, a donor/acceptor heterojunction is generally utilized in organic SCs in order to split coulombically bound exciton forming in organic semiconductors. Here, an organic pn homojunction SC showing high internal quantum efficiency of about 30% is reported. pn Homojunction was created by co-deposition of p or n type dopants and an organic semiconductor. An increase of the photocurrent density by more than 8 times, from the undoped device to pn homojunction device with 5% doping, was observed. The increase of photocurrent due to charge separation was assisted by the built-in potential near the pn homojunction interface that was controlled by doping concentration. The result demonstrated that the pn homojunction interface in a single organic semiconductor layer formed by doping can achieve efficient charge separation and provide a suitable alternative to the donor/acceptor interface that has been considered necessary for photoconversion in organic SCs. Image 1 • pn Homojunction in single organic semiconductor achieved efficient charge separation. • Increase of photocurrent by 8 times from undoped to 5% doping was observed. • Built-in potential at the pn homojunction was controlled by doping concentration. • Charge separation was assisted by a built-in potential near the pn homojunction. [ABSTRACT FROM AUTHOR]

The dependences of the mobility, the lifetime of deep traps and the range for hole- and electron-only devices on the ratio of metal-free phthalocyanine and fullerene in co-deposited films were measured by impedance spectroscopy. The ranges of the carriers were shown to be independent of the ratio of the co-deposited molecules. A multiple trapping model in which the disorder of the co-deposited molecules gives rise to shallow traps that dominate the mobility is proposed. Very long hole and electron ranges of 0.34 and 9.4 μm, which are long enough to extract carriers from co-deposited films in organic photovoltaic cells, were observed. [ABSTRACT FROM AUTHOR]

A dyad molecule was synthesized, with oligo( p -phenylenevinylene) (OPV) as the electron donor and naphthalene diimide (NDI) as the acceptor. The optical, thermal, and X-ray diffraction measurements of the film structure showed that the OPV and NDI moieties of the dyad crystallized separately in the spin-coated films. This is in striking contrast to the previously reported OPV and C 70 fullerene dyad, in which the introduction of C 70 severely disrupted the OPV packing. The separated crystallization in the OPV–NDI dyad was attributed to the planar shape of the acceptor and the differences in the crystalline structures of planar NDI and rod-like OPV. [ABSTRACT FROM AUTHOR]

Abstract: Low-band-gap dyad molecules containing diketopyrrolopyrole (DPP) chromophore and hexathiophene were designed and synthesized in combination with C60 and C70 derivatives as the electron acceptors. The effect of alkyl side chains in the donor parts on film morphology, thermal properties, and optical properties were investigated by X-ray diffraction analysis, differential scanning calorimetry, UV–vis absorption spectroscopy, and fluorescence spectroscopy. The donor part with a shorter alkyl side chain showed better packing of the π-plane and an enhancement of absorption in the longer-wavelength region, which led to higher J SC of organic solar cells. The use of C70 as the electron acceptor led to stronger absorption in the visible region, resulting in improved external quantum efficiency and J SC compared with those of the C60 derivatives. The single-component solar cell of the dyad with the methyl side chains and C70 derivative showed the power conversion efficiency of 0.84% with a relatively high J SC of 4.4mAcm−2 under AM 1.5 illumination (100mWcm−2). [Copyright &y& Elsevier]

Abstract: The Lattice Boltzmann Method (LBM) with a forcing scheme is used to simulate homogeneous isotropic turbulence, and the resolutions of 1283 and 2563 are compared. Two models, D3Q15 and D3Q19, are used in the investigation. Results demonstrate that the Lattice Boltzmann Method can capture important features of turbulence such as the vortex-like tubes and the Kolmogorov −5/3 power spectrum. Visualization of the elongated vortices using the high rotational identification method, , is also presented. For 2563, a longer range of the Kolmogorov −5/3 slope can be observed than in the case of 1283 grid points. As the resolution increases, the turbulence characteristics of the flow are found to become similar to those obtained in studies by the spectral method regardless of which model is used. [Copyright &y& Elsevier]

Efficient Interfacial Upconversion Enabling Bright Emission at an Extremely Low Driving Voltage in Organic Light-Emitting Diodes (Advanced Optical Materials 4/2022) Charge transfer states, donor/acceptor interface, driving voltage, organic light-emitting diodes, upconversion Keywords: charge transfer states; donor/acceptor interface; driving voltage; organic light-emitting diodes; upconversion EN charge transfer states donor/acceptor interface driving voltage organic light-emitting diodes upconversion 1 1 1 02/21/22 20220215 NES 220215 In article number 2101710, Seiichiro Izawa, Masahiro Morimoto, Shigeki Naka, and Masahiro Hiramoto report an efficient organic light-emitting diode (OLED), operable by a 1.5-V battery, that produces bright emission equivalent to the luminance of a typical display. [Extracted from the article]

Abstract: The structure at a spanwise edge of spreading turbulent region is studied in a wind tunnel experiment using conditional-sampling and ensemble-averaging techniques. A turbulent region is created by locally tripping the laminar boundary layer using two bi-morph piezoelectric actuators. The turbulent region protrudes into the laminar region at the middle height of the boundary layer. The results show that when the turbulent region spreads, a pair of streamwise vortices exists near the interface on the turbulent side, and the flow induced by the vortex pair pushes the turbulent fluid into the laminar region. An experiment in which a thin flat plate is inserted into the boundary layer reveals that the spanwise spreading of the turbulent region can be effectively suppressed by destroying these vortical structures. [Copyright &y& Elsevier]

The low-voltage operation of blue organic light-emitting diodes (OLEDs) is critical for reducing power consumption and improving device lifetime. This review briefly summarizes the history and origin of low-voltage electroluminescence and its realization in recent reports. In particular, upconversion OLEDs, which use the charge transfer state as an intermediate state to facilitate blue emission via triplet–triplet annihilation, present a promising solution. Thus, continued efforts aimed at reducing the driving voltage, including the exploration of new materials and device structures, are expected to significantly contribute to expanding the applications of blue OLEDs. • Turn-on voltages of blue OLEDs are reviewed. • Minimizing charge injection barriers is vital to reduce turn-on voltage. • Extremely low turn-on is realized in upconversion OLED via charge transfer state. [ABSTRACT FROM AUTHOR]

Low band gap dyad molecules were prepared that have absorption spectra matched well with the solar spectrum, and the construction of efficient charge transport pathways was observed. Under AM 1.5 illumination, the devices have achieved the highest JSC(4.79 mA cm2) and FF (0.46) in dyad-based organic solar cells to date. [ABSTRACT FROM AUTHOR]

In this study, the operation of donor/acceptor photovoltaic cells fabricated on homoepitaxially grown p-doped rubrene single-crystal substrates is demonstrated. The photocurrent density is dominated by the sheet conductivity (σ□) of the p-type single-crystal layer doped to 100 ppm with an iron chloride (Fe2Cl6) acceptor. A 65 μm thick p-type rubrene single-crystal substrate is expected to be required for a photocurrent density of 20 mA·cm−2. An entire bulk doping technique for rubrene single crystals is indispensable for the fabrication of practical organic single-crystal solar cells. [ABSTRACT FROM AUTHOR]

The π-conjugated rigid molecule Bph is a candidate for use as a channel system of single-molecule transistors. In this first-principles study, the practicality of the chemical modification of the channel molecule Bph for enhancing stability and improving performance is discussed. The insertion of methylene groups into the edges of a channel is suggested to enhance the stability of the cross-linking structures between electrodes because of the relaxation of S bonds. The calculation of electronic states and transmission indicates the sufficient on current of the methylene-inserted Bph derivative (Bph–CH2) in transistors through resonant tunneling. These results suggest the practicality of inserting methylene groups as a method of modifying channel molecules for achieving high stability and large on currents to realize single-molecule transistors. [ABSTRACT FROM AUTHOR]

A new optimization strategy based on system performance optimization life cycle (SPOLC) is introduced for high-performance lattice Boltzmann simulations of three-dimensional decaying isotropic turbulence. This strategy improves the performance of turbulent flow simulations in periodic boxes at different resolutions using the lattice Boltzmann method (LBM). The strategy improves the performance by modifying the lattice Boltzmann model, mathematical representation, computational algorithm, software implementation, and computing hardware utilization. The modifications include: (1) Establishing the slice concept as a logical grouping layer added to the LBM, applying an aggregation–disaggregation mechanism, enabling two-dimensional (2D) operation on the three-dimensional (3D) model, (2) improving lattice data access pattern by using an alternative one-dimensional (1D) array for numerical representation instead of the 3D cubic representation, (3) major reduction in memory access iterations by switching from function-wise iteration method to lattice-wise iteration method by applying code fusion to the streaming, velocity and collision model functions and iterations, (4) applying process parallelization and data vectorization, (5) achieving a much more efficient utilization of modern compute units by increasing the adaption of stream processing model. Furthermore, a correctness validation process has been applied by conducting lattice-wise value comparisons between the proposed solution output and the original implementation output. Simulations of decaying isotropic turbulence at resolutions ranging from 323 to 5123 using the LBM are carried out for these purposes. Calculations are performed on two systems with distinct specifications, to validate the effectiveness and portability of the SPOLC strategy. The calculation times are significantly reduced after applying the SPOLC strategy on S1 with the lattice Boltzmann relaxation time τ=0.503 by over 69% compared to S2’s original time, increasing to 95.47% at higher resolutions. Different features of the flow fields are depicted and their characteristics are discussed. Thin tubes are visualized, and the energy spectra are studied. All fields are initialized by a forced turbulent field simulated in a previous study using the LBM. [ABSTRACT FROM AUTHOR]

The energetic driving force for electron transfer must be minimized to realize efficient optoelectronic devices including organic light‐emitting diodes (OLEDs) and organic photovoltaics (OPVs). Exploring the dynamics of a charge‐transfer (CT) state at an interface leads to a comprehension of the relationship between energetics, electron‐transfer efficiency, and device performance. Here, we investigate the electron transfer from the CT state to the triplet excited state (T1) in upconversion OLEDs with 45 material combinations. By analyzing the CT emission and the singlet excited‐state emission from triplet–triplet annihilation via the dark T1, their energetics and electron‐transfer efficiencies are extracted. We demonstrate that the CT→T1 electron transfer is enhanced by the stronger CT interaction and a minimal energetic driving force (<0.1 eV), which is explained using the Marcus theory with a small reorganization energy of <0.1 eV. Through our analysis, a novel donor–acceptor combination for the OLED is developed and shows an efficient blue emission with an extremely low turn‐on voltage of 1.57 V. This work provides a solution to control interfacial CT states for efficient optoelectronic devices without energy loss. [ABSTRACT FROM AUTHOR]

The energetic driving force for electron transfer must be minimized to realize efficient optoelectronic devices including organic light‐emitting diodes (OLEDs) and organic photovoltaics (OPVs). Exploring the dynamics of a charge‐transfer (CT) state at an interface leads to a comprehension of the relationship between energetics, electron‐transfer efficiency, and device performance. Here, we investigate the electron transfer from the CT state to the triplet excited state (T1) in upconversion OLEDs with 45 material combinations. By analyzing the CT emission and the singlet excited‐state emission from triplet–triplet annihilation via the dark T1, their energetics and electron‐transfer efficiencies are extracted. We demonstrate that the CT→T1 electron transfer is enhanced by the stronger CT interaction and a minimal energetic driving force (<0.1 eV), which is explained using the Marcus theory with a small reorganization energy of <0.1 eV. Through our analysis, a novel donor–acceptor combination for the OLED is developed and shows an efficient blue emission with an extremely low turn‐on voltage of 1.57 V. This work provides a solution to control interfacial CT states for efficient optoelectronic devices without energy loss. [ABSTRACT FROM AUTHOR]

Despite the rapid progresses in the field of organic semiconductors, aided by the development of high-mobility organic materials, their high carrier mobilities are often unipolar, being sufficiently high only for either electrons or holes. Yet, the basic mechanisms underlying such significant mobility asymmetry largely remains elusive. We perform angle-resolved photoelectron spectroscopy to reveal the occupied band structures and the many-body interactions for low-mobility hole carriers in a typical n-type semiconductor perylene diimide derivative. The band dispersion exhibits strong renormalization to the calculated non-interacting electronic structure. The analysis including many-body interactions elucidate that the significant mass enhancement can be understood in terms of strong charge–phonon coupling, leading to an important mechanism of polaron band transport of low intrinsic carrier mobility in organic semiconductors. [ABSTRACT FROM AUTHOR]

The present study aims to simulate a collision of two droplets containing immiscible liquids by employing a three- dimensional incompressible smoothed particle hydrodynamics (SPH) method, with models implemented for the computation. The simulation of a head-on collision of two droplets, both of which contain the same glycerol solution, showed that the droplet behavior agrees very well with that observed in an experiment by Qian and Law (J Fluid Mech 331:59–80, 1997. 10.1017/S0022112096003722). The simulation of a head-on collision of a silicone oil droplet and a glycerol solution droplet showed that the droplet behavior agrees fairly well with that observed in the experiment by Planchette et al. (J Fluid Mech 702:5–25, 2012. 10.1017/jfm.2012.94). However, the oil only partially wraps the glycerol solution in the simulation, whereas in the experiment, the oil completely encapsulates the glycerol solution. The shape of the coalesced droplet at the early stage of the collision quantitatively agrees with that observed in the experiment. In the case of an offset collision of a droplet of silicone oil and a droplet of glycerol solution, the two droplets separate again, and small satellite droplets are formed after the collision; this behavior agrees well with that observed experimentally by Planchette et al. (2012). The feasibility of using simulations to estimate droplet liquid composition ratios is also presented. It is shown that the models implemented for the incompressible SPH simulation work reasonably well, and that this method can be a useful tool for studying the droplet collision phenomena. [ABSTRACT FROM AUTHOR]

Abstract Doped rubrene single-crystal photovoltaic cells were fabricated. Whole photocurrent generated in the pn -homojunction with the macroscopic area of 2 mm × 1 mm was confirmed to be collected through the p -doped homoepitaxial layer. A single-crystal substrate collected excitons to the pn -homojunction with the collection efficiency reaching 46%, owing to the long exciton diffusion length of 2.7 μm. Graphical abstract Image 1 Highlights • Doped rubrene single-crystal photovoltaic cells were fabricated. • Whole photocurrent generated in the pn -homojunction was confirmed to be collected through the p-doped homoepitaxial layer. • A single-crystal substrate collected excitons to the pn -homojunction with the collection efficiency reaching 46%. [ABSTRACT FROM AUTHOR]

Large energy losses in open-circuit voltage ( V OC ) are still an issue for the photo-conversion efficiency of organic solar cells (OSCs). We clarify the relationship between charge recombination and V OC loss for phthalocyanine/fullerene planar heterojunction (PHJ) OSCs. We quantify the V OC loss relative to the charge-transfer state energy by the temperature dependence of V OC . The charge recombination order obtained from impedance measurements indicates the presence of trap-assisted recombination. Our results suggest that the V OC losses are caused by the broad distribution of the tail state near the donor/acceptor (D/A) interface in the PHJ device. Thus, reducing the number of trap states near the D/A interface could lead to an increase in V OC . [ABSTRACT FROM AUTHOR]

In‐Plane Ferroelectric Memory In article number 2303032 by Yutaka Majima and co‐workers, in‐plane (IP) ferroelectric memory effect of a 100 nm channel‐length 2D ferroelectric semiconductor α‐In2Se3 stamped onto nanogap electrodes on Si/SiO2 is demonstrated. The non‐volatile memory characteristics with IP polarization including the on/off ratio reaching 103, stable retention lasting 17 hours, and endurance over 1200 cycles suggest a wide range of memory applications utilizing the lateral bottom contact structure. [ABSTRACT FROM AUTHOR]

In‐Plane Ferroelectric Memory In article number 2303032 by Yutaka Majima and co‐workers, in‐plane (IP) ferroelectric memory effect of a 100 nm channel‐length 2D ferroelectric semiconductor α‐In2Se3 stamped onto nanogap electrodes on Si/SiO2 is demonstrated. The non‐volatile memory characteristics with IP polarization including the on/off ratio reaching 103, stable retention lasting 17 hours, and endurance over 1200 cycles suggest a wide range of memory applications utilizing the lateral bottom contact structure. [ABSTRACT FROM AUTHOR]

Li@PCBM, the first neutral Li@C60 derivative, was synthesized. The Li@PCBM exists in a monomer-dimer equilibrium in solution but as a monomer in the PCBM matrix. The fully dispersed Li@PCBM n-doped the surrounding empty PCBM, raising the Fermi level by 0.13 eV compared with the undoped PCBM film. The hybrid films were utilized as an ETL for PSCs, promoting the efficiency of the device. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSCs) are promising low-cost devices for generating electricity. In addition to fill factor, the short circuit current density ( JSC) and the open circuit voltage ( VOC) are two key factors that have critical influence on the device performance. The energy levels of the donor and acceptor materials are crucial for achieving a high JSC and VOC. However, the interfacial structures between the organic materials substantially affect the JSC and VOC through the energy of the charge transfer (CT) states and the charge separation and recombination reaction kinetics. Here, it is reported that separating the donor and acceptor layer in bilayer OSCs with a thin insulating layer increases the energy of the CT state by weakening the Coulomb interaction at the interface and this also suppresses photoinduced CT and recombination. Although these effects usually increase VOC and decrease JSC, the trade-off is avoided by doping the insulating layer with a dye to utilize the energy transfer process. The increase in VOC without the reduction in JSC enhances the conversion efficiency of the OSCs by 30%. [ABSTRACT FROM AUTHOR]

Abstract: Harmonic analysis filtering methods are used to decompose 3D forced and decaying turbulent fields into coherent and incoherent parts. The filtering methods are the curvelets, wavelet and dual-tree complex wavelet filtering techniques. The methods are applied against the velocity fields of forced and decaying homogeneous isotropic turbulence. The velocity fields are generated using the Lattice Boltzmann Method (LBM) with a resolution of where the Taylor micro-scale Reynolds numbers are and for forced and decaying fields, respectively. The main objective of this study is to use other different filtering methods rather than depending only on wavelet and Fourier decompositions. Using different filtering methods may help in turbulence modeling, improving our knowledge about the structure of turbulent flow, choosing the appropriate filtering method and extracting general characteristics of the flow under study. Results show that the coherent and the random incoherent fields contribute to all scales in the inertial range, but the statistical behavior is different for each field. The three filtering methods approximately identify the coherent fields with the same geometrical shapes of the organized vortical structures. The statistical properties such as flatness, skewness and spectrum of the extracted fields (coherent and incoherent parts) are also investigated for each filtering method. The joint PDFs between the third and second invariants of the velocity gradient tensor are also studied. The joint PDFs for the coherent parts are found similar to previous topological studies of isotropic turbulence; however the incoherent PDFs show different topological features. [Copyright &y& Elsevier]

Perylene has had a tremendous impact in the history of material research for the molecular semiconductors. Among numerous derivatives of this polyaromatic hydrocarbon, perylene diimide (PDI) represents a promising class of organic materials envisioned as non-fullerene acceptors (NFAs) for the practical organic photovoltaic (OPV) applications due to their enhanced photo- and thermal stability and remarkably high electron affinity, some of which realize band-like transport properties. The present review guides some of the representative achievements in the development of rationally designed PDI systems, highlighting synthetic methodologies based on bay-functionalization strategies for creating well-designed molecular nanostructures and structure-performance relationship of perylene-based small molecular acceptors (SMAs) for the photovoltaic outcomes. [ABSTRACT FROM AUTHOR]

C60:Li@C60 hybrid n-type semiconducting films were first fabricated. The Fermi level of 1% Li@C60-added C60 films was determined to be −4.52 eV, which was 0.12 eV higher than that of pristine C60 films. A fraction of Li@C60 is distributed uniformly within the C60 film. Its application in PSCs was demonstrated, in which the addition of Li@C60 into a C60 film improved the device performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Afterglow materials have long emission lifetimes up to seconds to minutes. • We synthesize Eu2+, Dy3+@SrAl 2 O 4 , where emitting agents are co-doped in SrAl 2 O 4. • The liquid-state reaction plays a crucial role in the synthesis of materials. • Synthesis with a surfactant-template method yields product morphologies in 40–80 nm. • The hydrothermal method that produces morphologies up to approximately 2–3 μm. Afterglow materials, which are also known as persistent emitters, have a long emission lifetime that varies from seconds to tens of minutes. These materials have shown potential applications in photoenergy conservation devices such as evacuation signage and emitting lines in a motorway surface. In this study, we synthesized afterglow materials, Eu2+, Dy3+@SrAl 2 O 4 , wherein the emitting agents (Eu2+ and Dy3+) are co-doped in a SrAl 2 O 4 framework, which was confirmed by X-ray diffraction. The liquid-state reaction process plays a crucial role in the synthesis of materials. When the surfactant-template method is used for synthesis, reverse micelles, which control the morphology of afterglow product, hold the raw reactant materials, thereby yielding characteristic morphologies of approximately 40–80 nm. The reverse micelles have been detected by small-angle X-ray scattering in this study. In contrast, the hydrothermal method produces morphologies up to approximately 2–3 μm. Results suggest that both the synthetic routes yield similar emission spectra and mean afterglow time of ~ 10 s. [ABSTRACT FROM AUTHOR]

Homoepitaxial growth of organic semiconductor single crystals is a promising methodology toward the establishment of doping technology for organic opto-electronic applications. In this study, both electronic and crystallographic properties of homoepitaxially grown single crystals of rubrene were accurately examined. Undistorted lattice structures of homoepitaxial rubrene were confirmed by high-resolution analyses of grazing-incidence X-ray diffraction (GIXD) using synchrotron radiation. Upon bulk doping of acceptor molecules into the homoepitaxial single crystals of rubrene, highly sensitive photoelectron yield spectroscopy (PYS) measurements unveiled a transition of the electronic states, from induction of hole states at the valence band maximum at an adequate doping ratio (10 ppm), to disturbance of the valence band itself for excessive ratios (≥ 1000 ppm), probably due to the lattice distortion. [ABSTRACT FROM AUTHOR]

Clarifying critical differences in free charge generation and recombination processes between inorganic and organic semiconductors is important for developing efficient organic photoconversion devices such as solar cells (SCs) and photodetector. In this study, we analyzed the dependence of doping concentration on the photoconversion process at the organic pn-homojunction interface in a single organic semiconductor using the temperature dependence of J–V characteristics and energy structure measurements. Even though the organic pn-homojunction SC devices were fabricated using a single host material and the doping technique resembling an inorganic pn-homojunction, the charge generation and recombination mechanisms are similar to that of conventional donor/acceptor (D/A) type organic SCs; that is, the charge separation happens from localized exciton and charge transfer (CT) state being separated by the energy offset between adjacent molecules, and the recombination happens from localized charge carrier at two adjacent molecules. The determining factor for photoconversion processes is the localized nature of charges in organic semiconductors. The results demonstrated that controlling the delocalization of the charges is important to realize efficient organic photoconversion devices. [ABSTRACT FROM AUTHOR]