Dual Chalcogen-Bonding Interaction for High-Performance Filterless Narrowband Organic Photodetectors.

A novel green-absorbing organic molecule featuring dual intramolecular chalcogen bonds is synthesized and characterized. This molecule incorporates two such bonds: one between a tellurium atom and the oxygen atom of a carbonyl moiety, and the other between the tellurium atom and the adjacent nitrogen atom within a pyridine moiety. The molecule, featuring dual intramolecular chalcogen bonds exhibits a narrow absorption spectrum and elevated absorption coefficients, closely aligned with a resonance parameter of approximately 0.5. This behavior is due to its cyanine-like characteristics and favorable electrical properties, which are a direct result of its rigid, planar molecular structure. Therefore, this organic molecule forming dual intramolecular chalcogen bonds achieves superior optoelectronic performance in green-selective photodetectors, boasting an external quantum efficiency of over 65% and a full-width at half maximum of less than 95 nm while maintaining the performance after 1000 h of heating aging at 85 °C. Such organic photodetectors are poised to enhance stacked organic photodetector-on-silicon hybrid image sensors, paving the way for the next-generation of high-resolution and high-sensitivity image sensors.

Octupole moment driven free charge generation in partially chlorinated subphthalocyanine for planar heterojunction organic photodetectors.

In this study, high-performance organic photodetectors are presented which utilize a pristine chlorinated subphthalocyanine photoactive layer. Optical and optoelectronic analyses indicate that the device photocurrent is primarily generated through direct charge generation within the chlorinated subphthalocyanine layer, rather than exciton separation at layer interfaces. Molecular modelling suggests that this direct charge generation is facilitated by chlorinated subphthalocyanine high octupole moment (-80 DÅ2), which generates a 200 meV shift in molecular energetics. Increasing the thickness of chlorinated subphthalocyanine leads to faster response time, correlated with a decrease in trap density. Notably, photodetectors with a 50 nm thick chlorinated subphthalocyanine photoactive layer exhibit detectivities approaching 1013 Jones, with a dark current below 10-7 A cm-2 up to -5 V. Based on these findings, we conclude that high octupole moment molecular semiconductors are promising materials for high-performance organic photodetectors employing single-component photoactive layer.

The State-of-the-Art Solution-Processed Single Component Organic Photodetectors Achieved by Strong Quenching of Intermolecular Emissive State and High Quadrupole Moment in Non-Fullerene Acceptors.

A bulk-heterojunction (BHJ) blend is commonly used as the photoactive layer in organic photodetectors (OPDs) to utilize the donor (D)/acceptor (A) interfacial energetic offset for exciton dissociation. However, this strategy often complicates optimization procedures, raising serious concerns over device processability, reproducibility, and stability. Herein, highly efficient OPDs fabricated with single-component organic semiconductors are demonstrated via solution-processing. The non-fullerene acceptors (NFAs) with strong intrinsic D/A character are used as the photoactive layer, where the emissive intermolecular charge transfer excitonic (CTE) states are formed within <1 ps, and efficient photocurrent generation is achieved via strong quenching of these CTE states by reverse bias. Y6 and IT-4F-based OPDs show excellent OPD performances, low dark current density (≈10-9 A cm-2 ), high responsivity (≥0.15 A W-1 ), high specific detectivity (>1012 Jones), and fast photo-response time (<10 µs), comparable to the state-of-the-art BHJ OPDs. Together with strong CTE state quenching by electric field, these excellent OPD performances are also attributed to the high quadrupole moments of NFA molecules, which can lead to large interfacial energetic offset for efficient CTE dissociation. This work opens a new way to realize efficient OPDs using single-component systems via solution-processing and provides important molecular design rules.

Molecular orientation-dependent energetic shifts in solution-processed non-fullerene acceptors and their impact on organic photovoltaic performance.

The non-fullerene acceptors (NFAs) employed in state-of-art organic photovoltaics (OPVs) often exhibit strong quadrupole moments which can strongly impact on material energetics. Herein, we show that changing the orientation of Y6, a prototypical NFA, from face-on to more edge-on by using different processing solvents causes a significant energetic shift of up to 210 meV. The impact of this energetic shift on OPV performance is investigated in both bilayer and bulk-heterojunction (BHJ) devices with PM6 polymer donor. The device electronic bandgap and the rate of non-geminate recombination are found to depend on the Y6 orientation in both bilayer and BHJ devices, attributed to the quadrupole moment-induced band bending. Analogous energetic shifts are also observed in other common polymer/NFA blends, which correlates well with NFA quadrupole moments. This work demonstrates the key impact of NFA quadruple moments and molecular orientation on material energetics and thereby on the efficiency of high-performance OPVs.

Small Molecule Based Organic Photo Signal Receiver for High-Speed Optical Wireless Communications.

The present work describes the development of an organic photodiode (OPD) receiver for high-speed optical wireless communication. To determine the optimal communication design, two different types of photoelectric conversion layers, bulk heterojunction (BHJ) and planar heterojunction (PHJ), are compared. The BHJ-OPD device has a -3 dB bandwidth of 0.65 MHz (at zero bias) and a maximum of 1.4 MHz (at -4 V bias). A 150 Mbps single-channel visible light communication (VLC) data rate using this device by combining preequalization and machine learning (ML)-based digital signal processing (DSP) is demonstrated. To the best of the authors' knowledge, this is the highest data rate ever achieved on an OPD-based VLC system by a factor of 40 over the previous fastest reported. Additionally, the proposed OPD receiver achieves orders of magnitude higher spectral efficiency than the previously reported organic photovoltaic (OPV)-based receivers.

Harnessing Intramolecular Chalcogen-Chalcogen Bonding in Merocyanines for Utilization in High-Efficiency Photon-to-Current Conversion Optoelectronics.

A novel series of donor (D)-π-acceptor (A) merocyanine molecules harnessed with intramolecular chalcogen bonding (ChaB) is designed, synthesized, and characterized. ChaB comprises periodic chalcogen atoms, S, Se, and Te, and a neighboring oxygen atom of a carbonyl moiety. Compared to the D-π-A merocyanine dye with nontraditional intramolecular hydrogen bonding, the novel molecules with an intramolecular ChaB exhibit remarkably smaller absorption spectral widths and higher absorption coefficients attributed to their cyanine-like characteristics approaching the resonance parameter (c2) ∼0.5; furthermore, they exhibit better thermal stabilities and electrical charge-carrier transport properties in films. These novel D-π-A merocyanines harnessed with intramolecular ChaB networks are successfully utilized in high-performance color-selective organic photon-to-current conversion optoelectronic devices with excellent thermal stabilities. This study reports that the unique intramolecular ChaB plays an essential role in locking the molecular conformation of merocyanine molecules and enhancing the optical, thermal, and optoelectronic properties of high-performance and high-efficiency organic photon-to-current conversion devices.

Green-Light-Selective Organic Photodiodes with High Detectivity for CMOS Color Image Sensors.

Stacked structures employing wavelength-selective organic photodiodes (OPDs) have been studied as promising alternatives to the conventional Si-based image sensors because of their color constancy. Herein, novel donor (D)-π-acceptor (A) molecules are designed, synthesized, and characterized as green-light-selective absorbers for application in organic-on-Si hybrid complementary metal-oxide-semiconductor (CMOS) color image sensors. The p-type molecules, combined with two fused-type heterocyclic donors and an electron-accepting unit, exhibit cyanine-like properties that are characterized by intense and sharp absorption. This molecular design leads to improved absorption properties, thermal stability, and higher photoelectric conversion compared to those of a molecular design based on a nonfused ring. A maximum external quantum efficiency of 66% (λmax = 550 nm) and high specific detectivity (D*) of 8 × 1013 cm Hz1/2/W are achieved in an OPD consisting of a bulk heterojunction blend with two transparent electrodes on both sides. Finally, the green-light-detection capability of the narrow-band green-selective OPD is demonstrated by the optical simulation of an organic-on-Si hybrid, stacked-type, full-color photodetector comprising the green-light-selective OPD and a bottom Si photodiode with only blue and red color filters. Based on this molecular design, further optimization of the OPDs can allow the development of various optoelectronic sensors including 3D-stacked image sensors with enhanced sensitivities to replace the conventional Si-based CMOS image sensors.

Aqueous nanosilica dispersants for carbon nanotube.

Nanosilicas can disperse single-wall carbon nanotube (SWCNT) in aqueous solution efficiently; SWCNTs are stably dispersed in aqueous media for more than 6 months. The SWCNT dispersing solution with nanosilica can produce highly conductive transparent films which satisfy the requirements for application to touch panels. Even multiwall carbon nanotube can be dispersed easily in aqueous solution. The highly stable dispersion of SWCNTs in the presence of nanosilica is associated with charge transfer interaction which generates effective charges on the SWCNT particles, giving rise to electrostatic repulsion between the SWCNTs in the aqueous solution. Adhesion of charged nanosilicas on SWCNTs in the aqueous solution and a marked depression of the S11 peak of optical absorption spectrum of the SWCNT with nanosilicas suggest charge transfer interaction of nanosilicas with SWCNT. Thus-formed isolated SWCNTs are fixed on the flexible three-dimensional silica jelly structure in the aqueous solution, leading to the uniform and stable dispersion of SWCNTs.

Metal-semiconductor transition like behavior of naphthalene-doped single wall carbon nanotube bundles.

Naphthalene (N) or naphthalene-derivative (ND) adsorption-treatment evidently varies the electrical conductivity of single wall carbon nanotube (SWCNT) bundles over a wide temperature range due to a charge-transfer interaction. The adsorption treatment of SWCNTs with dinitronaphthalene molecules enhances the electrical conductivity of the SWCNT bundles by 50 times. The temperature dependence of the electrical conductivity of N- or ND-adsorbed SWCNT bundles having a superlattice structure suggests metal-semiconductor transition like behavior near 260 K. The ND-adsorbed SWCNT gives a maximum in the logarithm of electrical conductivity vs. T(-1) plot, which may occur after the change to a metallic state and be associated with a partial unravelling of the SWCNT bundle due to an evoked librational motion of the moieties of ND with elevation of the temperature.

Dynamic quantum molecular sieving separation of D2 from H2-D2 mixture with nanoporous materials.

Quantum molecular sieving separability of D(2) from an H(2)-D(2) mixture was measured at 77 K for activated carbon fiber, carbon molecular sieve, zeolite and single wall carbon nanotube using a flow method. The amount of adsorbed D(2) was evidently larger than H(2) for all samples. The maximum adsorption ratio difference between D(2) and H(2) was 40% for zeolite (MS13X), yielding a selectivity for D(2) with respect to H(2) of 3.05.

Simulation of dynamic behavior of surfactants on a hydrophobic surface using periodic-shell boundary molecular dynamics.

The adsorption and aggregation behaviors of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) on a hydrophobic graphite surface were examined using a novel molecular dynamics (MD) simulation with the periodic-shell boundary condition (PSBC). Differences in the adsorption behavior of SDS and CTAB molecules were clearly shown on the hydrophobic surface. Unexpectedly, the SDS molecules approached the graphite surface with their hydrophilic head groups. This unexpected approach mode was thought to be due to the aqueous layer on the graphite surface. The hydrophobic moiety of SDS molecules repeatedly adsorbed and desorbed on the graphite surface. In addition, SDS molecules kept moving on the graphite surface; thus, they did not form a stable adsorption layer. In contrast to SDS, the hydrophobic moiety of CTAB molecules approached the graphite surface at the primary step of adsorption. The hydrophobic moieties of CTAB molecules came close to each other, whereas the hydrophilic groups separated from one another. This result suggests that the CTAB molecules form molecular assemblies with a curved structure. The simulation results were consistent with the experimental observations. A clear difference between the adsorption behavior of SDS and CTAB molecules was revealed by MD simulations with PSBC.