Atto-Scale Noise Near-Infrared Organic Photodetectors Enabled by Controlling Interfacial Energetic Offset through Enhanced Anchoring Ability.

The near-infrared (NIR) sensor technology is crucial for various applications such as autonomous driving and biometric tracking. Silicon photodetectors (SiPDs) are widely used in NIR applications; however, their scalability is limited by their crystalline properties. Organic photodetectors (OPDs) have attracted attention for NIR applications owing to their scalability, low-temperature processing, and notably low dark current density (JD), which is similar to that of SiPDs. However, the still high JD (at NIR band) and few measurements of noise equivalent powers (NEPs) pose challenges for accurate performance comparisons. This study addresses these issues by quantitatively characterizing the performance matrix and JD generation mechanism using electron-blocking layers (EBLs) in OPDs. The energy offset at an EBL/photosensitive layer interface determines the thermal activation energy and directly affects JD. A newly synthesized EBL (3PAFBr) substantially enhances the interfacial energy barrier by forming a homogeneous contact owing to the improved anchoring ability of 3PAFBr. As a result, the OPD with 3PAFBr yields a noise current of 852 aA (JD = 12.3 fA cm⁻2 at V → -0.1 V) and several femtowatt-scale NEPs. As far as it is known, this is an ultralow of JD in NIR OPDs. This emphasizes the necessity for quantitative performance characterization.

Multifunctional Pt3Rh-Co3O4 alloy nanoparticles with Pt-enriched surface and induced synergistic effect for improved performance in ORR, OER, and HER.

Engineering high-performance electrocatalysts to improve the kinetics of parallel electrochemical reactions in low-temperature fuel cells, water splitting, and metal-air battery applications is important and inevitable. In this study, by employing a chemical co-reduction method, we developed multifunctional Pt3Rh-Co3O4 alloy with uniformly distributed ultrafine nanoparticles (2-3 nm), supported on carbon. The presence of Co3O4 and the incorporation of Rh led to a strong electronic and ligand effect in the Pt lattice environment, which caused the d-band center of Pt to shift. This shift improved the electrocatalytic performance of Pt3Rh-Co3O4 alloy. When Pt3Rh-Co3O4/C was used to catalyze the oxygen reduction reaction (E1/2: 0.75 V), oxygen evolution reaction (η10: 290 mV), and hydrogen evolution reaction (η10: 55 mV), it showed greater endurance (mass activity loss of only 7%-17%) than Pt-Co3O4/C and Pt/C catalysts up to 5000 potential cycles in perchloric acid. Overall, the as-prepared Pt3Rh-Co3O4/C showed high multifunctional electrocatalytic potency, as demonstrated by typical electrochemical studies, and its physicochemical properties endorse their extended performance for a wide range of energy storage and conversion applications.

Polyhedron shaped palladium nanostructures embedded on MoO2/PANI-g-C3N4 as high performance and durable electrocatalyst for oxygen reduction reaction.

A hybrid catalyst support anchoring a noble metal catalyst could be a promising material for building interfacial bonding between metallic nanostructures and polymer functionalized carbon supports to improve the kinetics of oxygen reduction reaction (ORR). This study successfully prepared a polyhedron nanostructured Pd and MoO2-embedded polyaniline-functionalized graphitized carbon nitride (PANI-g-C3N4) surface using a chemical reduction method. The Pd-Mo/PANI-g-C3N4 achieved an ORR activity of 0.27 mA µg-1 and 1.14 mA cm-2 at 0.85 V, which were 4.5 times higher than those of commercial 20% Pt/C catalyst (0.06 mA µg-1 and 0.14 mA cm-2). In addition, the Pd-Mo/PANI-g-C3N4 retained âˆ¼ 77.5% of its initial mass activity after 10,000 cycles, with only 30 mV half-wave potential reduction. Further, the engineered potential active sites in the catalyst material verified the significant improvement in the ORR activity of the catalyst with increased life-time, and theoretical calculations revealed that the synergistic effect of the catalytic components enhanced the ORR kinetics of the active sites.

Highly Effective Thermally Activated Delayed Fluorescence Emitters Based on Symmetry and Asymmetry Nicotinonitrile Derivatives.

In this study, we developed two thermally activated delayed fluorescence (TADF) emitters, ICzCN and ICzCYP, to apply to organic light-emitting diodes (OLEDs). These emitters involve indolocarbazole (ICz) donor units and nicotinonitrile acceptor units with a twisted donor-acceptor-donor (D-A-D) structure for small singlet (S1) and triplet (T1) state energy gap (ΔEST) to enable efficient exciton transfer from the T1 to the S1 state. Depending on the position of the cyano-substituent, ICzCN has a symmetric structure by introducing donor units at the 3,5-position of isonicotinonitrile, and ICzCYP has an asymmetric structure by introducing donor units at the 2,6-position of nicotinonitrile. These emitters have different properties, such as the maximum luminance (Lmax) value. The Lmax of ICzCN reached over 10000 cd m-2. The external quantum efficiency (ηext) was 14.8% for ICzCN and 14.9% for ICzCYP, and both achieved a low turn-on voltage (Von) of less than 3.4 eV.

Thin-Film Luminescent Solar Concentrator Based on Intramolecular Charge Transfer Fluorophore and Effect of Polymer Matrix on Device Efficiency.

Luminescent solar concentrators (LSCs) provide a transformative approach to integrating photovoltaics into a built environment. In this paper, we report thin-film LSCs composed of intramolecular charge transfer fluorophore (DACT-II) and discuss the effect of two polymers, polymethyl methacrylate (PMMA), and poly (benzyl methacrylate) (PBzMA) on the performance of large-area LSCs. As observed experimentally, DACT-II with the charge-donating diphenylaminocarbazole and charge-accepting triphenyltriazine moieties shows a large Stokes shift and limited re-absorption losses in both polymers. Our results show that thin-film LSC (10 × 10 × 0.3 cm3) with optimized concentration (0.9 wt%) of DACT-II in PBzMA gives better performance than that in the PMMA matrix. In particular, optical conversion efficiency (ηopt) and power-conversion efficiency (ηPCE) of DACT-II/PBzMA LSC are 2.32% and 0.33%, respectively, almost 1.2 times higher than for DACT-II/PMMA LSC.

Highly effective organic light-emitting diodes containing thermally activated delayed fluorescence emitters with horizontal molecular orientation.

In this study, we report new thermally activated delayed fluorescence (TADF) emitters, AcPYM (10,10'-(pyrimidine-2,5-diylbis(4,1-phenylene))bis(9,9-dimethyl-9,10-dihydroacridine)) and PxPYM (10,10'-(pyrimidine-2,5-diylbis(4,1-phenylene))bis(10H-phenoxazine)), by employing donor units at the 2,5-positions of the pyrimidine acceptor unit. The donor-acceptor-donor (D-A-D) units combined in the linear molecular structure of AcPYM or PxPYM enhanced the horizontally oriented alignment, and the horizontal transition dipole moments were realized by up to 87% in the host matrix. Organic light-emitting diodes (OLEDs) containing AcPYM and PxPYM emitters realized external quantum efficiencies (η ext) of 16.8% for blue and green emissions.

Direct Patterning of a Carbon Nanotube Thin Layer on a Stretchable Substrate.

Solution-based direct patterning on an elastomer substrate with meniscus-dragging deposition (MDD) enables fabrication of very thin carbon nanotube (CNT) layers in the nanometer scale (80-330 nm). To fabricate the CNT pattern with CNT solution, contact angle, electrical variation, mechanical stress, and surface cracks of elastomer substrate were analyzed to identify the optimal conditions of O2 treatment (treatment for 30 s with RF power of 50 W in O2 atmosphere of 50 sccm) and mixture ratio between Ecoflex and polydimethylsiloxane (PDMS) (Ecoflex:PDMS = 5:1). The type of mask for patterning of the CNT layer was determined through quantitative analysis for sharpness and uniformity of the fabricated CNT pattern. Through these optimization processes, the CNT pattern was produced on the elastomer substrate with selected mask (30 µm thick oriented polypropylene). The thickness of CNT pattern was also controlled to have hundreds nanometer and 500 µm wide rectangular and circular shapes were demonstrated. Furthermore, the change in the current and resistance of the CNT layer according to the applied strain on the elastomer substrate was analyzed. Our results demonstrated the potential of the MDD method for direct CNT patterning with high uniformity and the possibility to fabricate a stretchable sensor.

Precise control of nanoscale spacing between electrodes using different natured self-assembled monolayers.

Herein, we introduce an interdigitated horizontal electrode (IHE) structure with a metal-based electron-collecting (or -injecting) electrode and a hole-collecting (or -injecting) electrode composed of a conductive polymeric material that has a nanoscale distance and is horizontally separated. In the IHE, a metal electrode is fabricated on a silicon-oxide substrate, and a self-assembled monolayer (SAM) is selectively bonded to the metal and the oxide to form a conductive polymer electrode by dip coating. Each of the SAM materials is composed of a head part bonded to the substrate surface and a tail part that is hydrophilic or hydrophobic. This inherent property makes the metal electrode hydrophobic and the oxide substrate hydrophilic. Ag is used as a metal electrode material and is combined with alkanethiol SAMs. The alkylsilane SAMs are combined with the silicon oxide substrate to make them hydrophilic, using poly (3, 4-ethylenedioxythiophene)-poly (PEDOT: PSS) as the conductive polymer material. In this study, we have found that there is a difference in the spacing between the two electrodes that depends on the combination of SAM materials. Each interval was spaced from a minimum of 140 nm to a maximum of 385 nm.

An Alternative Host Material for Long-Lifespan Blue Organic Light-Emitting Diodes Using Thermally Activated Delayed Fluorescence.

It has been challenging to find stable blue organic light emitting diodes (OLEDs) that rely on thermally activated delayed fluorescence (TADF). Lack of stable host materials well-fitted to the TADF emitters is one of the critical reasons. The most popular host for blue TADF, bis[2-(diphenylphosphino)phenyl] ether oxide (DPEPO), leads to unrealistically high maximum external quantum efficiency. DPEPO is however an unstable material and has a poor charge transporting ability, which in turn induces an intrinsic short OLED operating lifespan. Here, an alternative host material is introduced which educes the potential efficiency and device lifespan of given TADF emitters with the appropriateness of replacing the most popular host material, DPEPO, in developing blue TADF emitters. It simultaneously provides much longer device lifespan and higher external quantum efficiency at a practical brightness due to its high material stability and electron-transport-type character well-fitted for hole-transport-type TADF emitters.

Blue Oleds: High-Efficiency Blue Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence from Phenoxaphosphine and Phenoxathiin Derivatives (Adv. Mater. 23/2016).

High-performance blue thermally activated delayed fluorescence (TADF) emitters containing a phenoxaphosphine oxide or phenoxathiin dioxide acceptor unit coupled with a dimethylacridan donor unit are developed by T. Yasuda and co-workers, as desribed on page 4626. These emitters can allow efficient up-conversion of triplet excitons into singlet excitons, leading to both photoluminescence and internal electroluminescence quantum efficiencies of up to nearly 100%.

High-Efficiency Blue Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence from Phenoxaphosphine and Phenoxathiin Derivatives.

High-efficiency blue thermally activated delayed fluorescence (TADF) molecules, consisting of phenoxaphosphine oxide and phenoxathiin dioxide as acceptor units and 9,9-dimethylacridan as a donor unit, are reported. Maximum external electroluminescence quantum efficiencies of up to 20.5% are achieved in blue organic light-emitting diodes (OLEDs) by employing these materials as TADF emitters.

Thermally Activated Delayed Fluorescence Polymers for Efficient Solution-Processed Organic Light-Emitting Diodes.

Thermally activated delayed fluorescence (TADF) π-conjugated polymers are developed for solution-processed TADF-OLEDs. Benzophenone-based alternating donor-acceptor structures contribute to the small ∆EST , enabling efficient exciton-harvesting through TADF. Solution-processed OLEDs using the TADF polymers as emitters can achieve high maximum external electroluminescence efficiencies of up to 9.3%.

Nearly 100% internal quantum efficiency in undoped electroluminescent devices employing pure organic emitters.

The design of efficient and concentration-insensitive metal-free thermally activateddelayed fluorescence (TADF) materials is reported. Blue and green organic light-emitting diodes (OLEDs) containing a hole-transport layer, an undoped TADF emissive layer, and an electron-transport layer achieve maximum external quantum efficiencies of 19%, which is comparable to the best doped OLEDs.

X-shaped benzoylbenzophenone derivatives with crossed donors and acceptors for highly efficient thermally activated delayed fluorescence.

Thermally activated delayed fluorescence (TADF) materials based on benzoylbenzophenone, AcPmBPX and PxPmBPX, were designed and synthesized. Organic light-emitting diodes using these materials as emitters exhibited high external electroluminescence quantum efficiencies of up to 11%.

Highly efficient blue electroluminescence based on thermally activated delayed fluorescence.

Organic compounds that exhibit highly efficient, stable blue emission are required to realize inexpensive organic light-emitting diodes for future displays and lighting applications. Here, we define the design rules for increasing the electroluminescence efficiency of blue-emitting organic molecules that exhibit thermally activated delayed fluorescence. We show that a large delocalization of the highest occupied molecular orbital and lowest unoccupied molecular orbital in these charge-transfer compounds enhances the rate of radiative decay considerably by inducing a large oscillator strength even when there is a small overlap between the two wavefunctions. A compound based on our design principles exhibited a high rate of fluorescence decay and efficient up-conversion of triplet excitons into singlet excited states, leading to both photoluminescence and internal electroluminescence quantum yields of nearly 100%.

Luminous butterflies: efficient exciton harvesting by benzophenone derivatives for full-color delayed fluorescence OLEDs.

Butterfly-shaped luminescent benzophenone derivatives with small energy gaps between their singlet and triplet excited states are used to achieve efficient full-color delayed fluorescence. Organic light-emitting diodes (OLEDs) with these benzophenone derivatives doped in the emissive layer can generate electroluminescence ranging from blue to orange-red and white, with maximum external quantum efficiencies of up to 14.3%. Triplet excitons are efficiently harvested through delayed fluorescence channels.