Electron Transfer Enhanced by a Minimal Energetic Driving Force at the Organic-Semiconductor Interface.

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 (T) in upconversion OLEDs with 45 material combinations.

Efficient Spin Interconversion by Molecular Conformation Dynamics of a Triplet Pair for Photon Up-Conversion in an Amorphous Solid.

Solid-state materials with improved light-to-energy conversions in organic photovoltaics and in optoelectronics are expected to be developed by realizing efficient triplet-triplet annihilation (TTA) by manipulating the spin conversion processes to the singlet state. In this study, we elucidate the spin conversion mechanism for delayed fluorescence by TTA from a microscopic view of the molecular conformations. We examine the time evolution of the electron spin polarization of the triplet-pair state (TT state) in an amorphous solid-state system exhibiting highly efficient up-conversion emission by using time-resolved electron paramagnetic resonance.

Wavily Curved Perylene Diimides: Synthesis, Characterization, and Photovoltaic Properties.

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.

Evaporable Fullerene Indanones with Controlled Amorphous Morphology as Electron Transport Layers for Inverted Perovskite Solar Cells.

Fullerenes are among the most commonly used electron-transporting materials (ETMs) in inverted perovskite solar cells (IPSCs). Although versatile functionalized fullerene derivatives have shown excellent performance in IPSCs, pristine [60]fullerene (C) is still the most widely used in devices mainly because of its uniform morphology by thermal deposition. However, thermally evaporable fullerene derivatives have not yet been achieved.

Blue organic light-emitting diode with a turn-on voltage of 1.47 V.

Among the three primary colors, blue emission in organic light-emitting diodes (OLEDs) are highly important but very difficult to develop. OLEDs have already been commercialized; however, blue OLEDs have the problem of requiring a high applied voltage due to the high-energy of blue emission. Herein, an ultralow voltage turn-on at 1.

Bottom Contact 100 nm Channel-Length α-In Se In-Plane Ferroelectric Memory.

Owing to the emerging trend of non-volatile memory and data-centric computing, the demand for more functional materials and efficient device architecture at the nanoscale is becoming stringent. To date, 2D ferroelectrics are cultivated as channel materials in field-effect transistors for their retentive and switchable dipoles and flexibility to be compacted into diverse structures and integration for intensive production. This study demonstrates the in-plane (IP) ferroelectric memory effect of a 100 nm channel-length 2D ferroelectric semiconductor α-In Se stamped onto nanogap electrodes on Si/SiO under a lateral electric field.

Synthesis of neutral Li-endohedral PCBM: an n-dopant for fullerene derivatives.

Li@PCBM, the first neutral Li@C 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.

Quasi-Homoepitaxial Junction of Organic Semiconductors: A Structurally Seamless but Electronically Abrupt Interface between Rubrene and Bis(trifluoromethyl)dimethylrubrene.

Single-crystalline organic semiconductors exhibiting band transport have opened new possibilities for the utilization of efficient charge carrier conduction in organic electronic devices. The epitaxial growth of molecular materials is a promising route for the realization of well-crystallized organic semiconductor p-n junctions for optoelectronic applications enhanced by the improved charge carrier mobility. In this study, the formation of a high-quality crystalline interface upon "quasi-homoepitaxial" growth of bis(trifluoromethyl)dimethylrubrene (fmRub) on the single-crystal surface of rubrene was revealed by using out-of-plane and grazing-incidence X-ray diffraction techniques.

Influence of N-Substituents on Photovoltaic Properties of Singly Bay-Linked Dimeric Perylene Diimides.

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.

Curved Perylene Diimides Fused with Seven-Membered Rings.

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.

Development of Perylene-Based Non-Fullerene Acceptors through Bay-Functionalization Strategy.

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.

Donor/Acceptor Photovoltaic Cells Fabricated on -Doped Organic Single-Crystal Substrates.

In this study, the operation of donor/acceptor photovoltaic cells fabricated on homoepitaxially grown -doped rubrene single-crystal substrates is demonstrated. The photocurrent density is dominated by the sheet conductivity (σ) of the -type single-crystal layer doped to 100 ppm with an iron chloride (FeCl) acceptor. A 65 mm thick type rubrene single-crystal substrate is expected to be required for a photocurrent density of 20 mA·cm.

Electronic and Crystallographic Examinations of the Homoepitaxially Grown Rubrene Single Crystals.

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.

Photoconversion Mechanism at the -Homojunction Interface in Single Organic Semiconductor.

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 -homojunction interface in a single organic semiconductor using the temperature dependence of characteristics and energy structure measurements. Even though the organic -homojunction SC devices were fabricated using a single host material and the doping technique resembling an inorganic -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.

Regioselective Bay-Functionalization of Perylenes Toward Tailor-Made Synthesis of Acceptor Materials for Organic Photovoltaics.

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 C -symmetric dibromide by a controlled monoetherification and a final bromination.

Li@C endohedral fullerene as a supraatomic dopant for C electron-transporting layers promoting the efficiency of perovskite solar cells.

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.

Parts-per-Million-Level Doping Effects in Organic Semiconductor Films and Organic Single Crystals.

Controlling the pn-type behavior of a semiconductor such as silicon by adding an extremely small quantity of an impurity (doping) is a central part of inorganic semiconductor electronics since the 20th century. Recent progress in the doping of organic semiconductors strongly suggests the advent of a new era of doped organic semiconductors. Here, the principles and effects of doping at the level of parts per million (ppm) in organic semiconductor films and single crystals are described, including descriptions of complete pn-control, doping sensitization, ppm doping using an extremely low-speed deposition technique reaching 10 nm s , and emerging ppm-level doping effects, such as trap filling, majority carriers, homojunction formation, and decreased mobility, as well as ppm-level doping effects in organic single crystals measured by the Hall effect, which shows a doping efficiency of 24%.

Effect of Band Bending and Energy Level Alignment at the Donor/Acceptor Interface on Open-Circuit Voltage in Organic Solar Cells.

Open-circuit voltage ( V) is a key parameter governing the power conversion efficiency of organic solar cells. We clarified the effect of band bending in organic semiconductor films on the V of phthalocyanine (HPc)/fullerene (C) planar heterojunction (PHJ) OSCs. The V was significantly affected by the HPc layer thickness, varying from 0.

Crystallization and Polymorphism of Organic Semiconductor in Thin Film Induced by Surface Segregated Monolayers.

Preparation of highly crystalline organic semiconductor films is vital to achieving high performance in electronic devices. Here we report that surface segregated monolayers (SSMs) on top of phenyl-C-butyric acid methyl ester (PCBM) thin films induce crystal growth in the bulk, resulting in a dramatic change in the structure to form a new crystal phase. Highly ordered crystalline films with large domain sizes of several hundreds of nanometers are formed with uniaxial orientation of the crystal structure perpendicular to the substrate.

Hall Effect in Bulk-Doped Organic Single Crystals.

The standard technique to separately and simultaneously determine the carrier concentration per unit volume (N, cm ) and the mobility (μ) of doped inorganic single crystals is to measure the Hall effect. However, this technique has not been reported for bulk-doped organic single crystals. Here, the Hall effect in bulk-doped single-crystal organic semiconductors is measured.

Electrochemical Detection of Circadian Redox Rhythm in Cyanobacterial Cells via Extracellular Electron Transfer.

Recent research on cellular circadian rhythms suggests that the coupling of transcription-translation feedback loops and intracellular redox oscillations is essential for robust circadian timekeeping. For clarification of the molecular mechanism underlying the circadian rhythm, methods that allow for the dynamic and simultaneous detection of transcription/translation and redox oscillations in living cells are needed. Herein, we report that the cyanobacterial circadian redox rhythm can be electrochemically detected based on extracellular electron transfer (EET), a process in which intracellular electrons are exchanged with an extracellular electrode.

Dominant effects of first monolayer energetics at donor/acceptor interfaces on organic photovoltaics.

Energy levels of the first monolayer are manipulated at donor/acceptor interfaces in planar heterojunction organic photovoltaics by using molecular self-organization. A "cascade" energy landscape allows thermal-activation-free charge generation by photoirradiation, destabilizes the energy of the interfacial charge-transfer state, and suppresses bimolecular charge recombination, resulting in a higher open-circuit voltage and fill factor.

All-Polymer Solar Cell with High Near-Infrared Response Based on a Naphthodithiophene Diimide (NDTI) Copolymer.

Polymer-blend solar cells (all-PSCs) based on a copolymer of naphthodithiophene diimide and bithiophene (PNDTI-BT-DT) as a near-infrared absorber as well as an electron acceptor were fabricated in combination with PTB7 as an electron donor. Notably, the external quantum efficiency spectra of the all-PSCs demonstrated photoresponse up to 900 nm with the efficiency of 25% at 800 nm, which is much higher than that for the previously reported all-PSCs. Power conversion efficiency as high as 2.

Surface functionalization of organic semiconductor films by segregated monolayers.

Fullerene-based surfactants with semifluoroalkyl chains bearing one of five different functional groups at the end were synthesized and used for the facile surface modification of organic semiconductor films. Surface analysis showed that the modifiers were segregated and the functional groups were exposed at the surface.

Morphological stability of organic solar cells based upon an oligo(p-phenylenevinylene)-C70 dyad.

An oligo(p-phenylenevinylene)-C(70) dyad achieves the highest power conversion efficiency (1.92%) in dyad-based organic solar cells to date. Covalent attachment in the dyad prevents large phase separation, resulting in good morphological and device stability at high temperatures as compared with mixed bulk heterojunction devices.