Organic Heterostructures Research Articles

Selective epitaxial growth of organic heterostructure via cocrystal engineering: Towards oriented signal conversion

Selective epitaxial growth of organic heterostructure via cocrystal engineering: Towards oriented signal conversion

Spatially Resolved Organic Whispering-Gallery-Mode Hetero-Microrings for High-Security Photonic Barcodes.

Whispering-gallery-mode (WGM) microcavities featuring distinguishable sharp peaks in a broadband exhibit enormous advantages in the field of miniaturized photonic barcodes. However, such kind of barcodes developed hitherto are primarily based on microcavities wherein multiple gain medias were blended into a single matrix, thus resulting in the limited and indistinguishable coding elements. Here, a surface tension assisted heterogeneous assembly strategy is proposed to construct the spatially resolved WGM hetero-microrings with multiple spatial colors along its circular direction. Through precisely regulating the charge-transfer (CT) strength, full-color microrings covering the entire visible range were effectively acquired, which exhibit a series of sharp and recognizable peaks and allow for the effective construction of high-quality photonic barcodes. Notably, the spatially resolved WGM hetero-microrings with multiple coding elements were finally acquired through heterogeneous nucleation and growth controlled by the directional diffusion between the hetero-emulsion droplets, thus remarkably promoting the security strength and coding capacity of the barcodes. The results would be useful to fabricate new types of organic hierarchical hybrid WGM heterostructures for optical information recording and security labels.

Spatially Resolved Organic Whispering‐Gallery‐Mode Hetero‐Microrings for High‐Security Photonic Barcodes

AbstractWhispering‐gallery‐mode (WGM) microcavities featuring distinguishable sharp peaks in a broadband exhibit enormous advantages in the field of miniaturized photonic barcodes. However, such kind of barcodes developed hitherto are primarily based on microcavities wherein multiple gain medias were blended into a single matrix, thus resulting in the limited and indistinguishable coding elements. Here, a surface tension assisted heterogeneous assembly strategy is proposed to construct the spatially resolved WGM hetero‐microrings with multiple spatial colors along its circular direction. Through precisely regulating the charge‐transfer (CT) strength, full‐color microrings covering the entire visible range were effectively acquired, which exhibit a series of sharp and recognizable peaks and allow for the effective construction of high‐quality photonic barcodes. Notably, the spatially resolved WGM hetero‐microrings with multiple coding elements were finally acquired through heterogeneous nucleation and growth controlled by the directional diffusion between the hetero‐emulsion droplets, thus remarkably promoting the security strength and coding capacity of the barcodes. The results would be useful to fabricate new types of organic hierarchical hybrid WGM heterostructures for optical information recording and security labels.

Laterally Engineering Organic Light-Harvesting Monolithic Heterostructures for Spatially Resolved Photonic Barcodes

Laterally Engineering Organic Light-Harvesting Monolithic Heterostructures for Spatially Resolved Photonic Barcodes

Homogenous Hyperbranched Networks Enabling Anisotropic Photon Transport and Polarization Filtering

AbstractIntegrated hierarchical microstructures composed of organic micro/nanocrystals with defined morphology have received great interest as candidates for advanced photonic circuits. Herein, the synthesis of highly ordered multilevel homogenous hyperbranched networks (HHNs) made of the individual organic compound 2, 3‐dicyanine naphthalene via a facile solution self‐assembly route is reported. The selective growth of branches on the sidewall of the backbone driven by the lattice match mechanism leads to the formation of higher‐level snowflake‐like configuration of the HHNs. These well‐organized HHNs perform excellent abilities of directional asymmetry photon transport and hierarchical polarization filtering. Combined with the doping strategy, the broad emission range of hyperbranched network heterostructures is expanded, and even the white light emission with Commission Internationale de L'Eclairage coordinates at (0.30, 0.33) is realized. This work provides deep insight into the rational creation of complex organic heterostructures for novel photoelectric devices with desired performances.

A novel molecularly imprinted photoelectrochemical aptasensor based on dual recognition mechanism for ultratrace detection of plasticizer dibutyl phthalate

Dibutyl phthalate (DBP) is one of the main phthalate plasticizer pollutants in the environment, which can seriously affect the endocrine and immune systems of animals and plants, and raise the risk of cancer, mutagenesis, reproductive malformation and other diseases. The present work aimed to develop a simple, rapid and ultrasensitive photoelectrochemical (PEC) sensor for DBP detection. By incorporating aptamer recognition mechanism with molecular imprinted technology (MIT), a dual identification strategy was proposed based on metal organic framework (MOF) and Cu2O heterostructure, which was synthesized in situ by electrodeposition and a simple immersion method. Specially, the novel PEC sensor was exploited by controllable self-polymerization of dopamine with the complex formed by Aptamer [DBP] and DBP incubation on the surface of Cu3(BTC)2/Cu2O/ITO. Owing to the strong light adsorption ability, good stability and enhanced photocurrent of Cu3(BTC)2/Cu2O hybrid under visible light irradiation, and also to the double recognition mechanism of aptamer and MIT, the PEC sensor exhibited highly specific determination of DBP. Under optimal experimental conditions, the designed sensor achieved a linear range from 0.1 pM to 1.0 nM and an extremely low detection limit of 0.035 pM. Moreover, it showed good reliability and practicability in real samples assay. This study extended the development of PEC sensor in plasticizer contaminant detection.

Supramolecular Copolymers Under Kinetic, Thermodynamic, or Pathway-Switching Control.

Supramolecular copolymers have attracted much attention due to their potential functionalities. However, the co-assembly strategies to construct co-assemblies of small molecules with well-defined sequence structures are stilllimited, especially for more complex crystalline block co-assemblies. Herein, we target this challenge by designing Ir(III) complexes 1 and 2, which possess unique self-assembly pathways and are capable of forming crystalline assemblies in aqueous systems. Specifically, block and random co-assemblies of 1 and 2 can be synthesized by kinetic and thermodynamic control, respectively. Meanwhile, by adjusting the water content to orthogonalize the on-pathway and the off-pathway, an unprecedented pathway-switching approach is realized to synthesize block and random co-assemblies. By coupling kinetic pathways, the present co-assembly strategies are expected to pave the way for the synthesis of crystalline co-assemblies of small molecules and the construction of organic heterostructures.

Supramolecular Copolymers Under Kinetic, Thermodynamic, or Pathway‐Switching Control

AbstractSupramolecular copolymers have attracted much attention due to their potential functionalities. However, the co‐assembly strategies to construct co‐assemblies of small molecules with well‐defined sequence structures are still limited, especially for more complex crystalline block co‐assemblies. Herein, we target this challenge by designing IrIII complexes 1 and 2, which possess unique self‐assembly pathways and are capable of forming crystalline assemblies in aqueous systems. Specifically, block and random co‐assemblies of 1 and 2 can be synthesized by kinetic and thermodynamic control, respectively. Meanwhile, by adjusting the water content to orthogonalize the on‐pathway and the off‐pathway, an unprecedented pathway‐switching approach is realized to synthesize block and random co‐assemblies. By coupling the kinetic pathways, the present co‐assembly strategies are expected to pave the way for the synthesis of crystalline co‐assemblies of small molecules and the construction of organic heterostructures.

Directional Self-Assembly of Facet-Aligned Organic Hierarchical Super-Heterostructures for Spatially Resolved Photonic Barcodes.

Organic multicolor heterostructures with spatially resolved luminescent colors and identifiable patterns have exhibited considerable potential for achieving micro-/nanoscale photonic barcodes. Nevertheless, such types of barcodes reported thus far are exclusively based on a single heterostructure with limited coding elements. Here, a directional self-assembly strategy is proposed to achieve high-coding-capacity spatially resolved photonic barcodes through rationally constructing organic hierarchical super-heterostructures, where numerous subheterostructure blocks with flat hexagonal facets are precisely oriented with their specific facets via a reconfigurable capillary force. The building blocks were prepared through a one-pot sequential heteroepitaxial growth, which enables the effective modulation of the structural and color characteristics in coding structures. Significantly, a directional facet-to-facet attraction between particles via facet registration leads to the formation of well-defined 1D super-heterostructures, which contain multiple coding elements, thus providing a good platform for constructing the high-coding-capacity photonic barcodes. The results may be useful in fabricating organic hierarchical hybrid super-heterostructures for security labels and optical data recording.

Tuning the surface electronic structure of WS2 with Zn- and Cu-phthalocyanine for improved hydrogen evolution reaction: Experimental and DFT investigation

WS2 nanosheets have been successfully demonstrated to be promising materials for several important catalytic reactions including Hydrogen Evolution Reaction (HER) and Oxygen Reduction Reactions (ORR) either standalone or by functionalizing and as composites. Tungsten disulfide (WS2) is known to exist in two phases: 2H semiconducting and 1 T conducting. The 2H phase is commonly obtained by simple exfoliation of bulk WS2. Due to the semiconducting nature of the 2H phase, catalytic activity towards HER is very feeble compared to its 1 T counterpart. In this work, we have enhanced the activity of 2H WS2 nanosheets by interfacial modification through metal phthalocyanine (Pc) molecule (Cu-Pc and Zn-Pc) functionalization. We observe that the HER activity shows significant enhancement with the functionalization, with Zn-Pc showing better performance than the Cu-Pc. This functionalization creates an electronically coupled inorganic–organic heterostructure which shows improved response to HER. The WS2 functionalized nanosheets were studied in-depth with X-ray diffraction (XRD), X-ray photo electron spectroscopy (XPS) and High-Resolution Transmission Electron Microscopy (HRTEM) analyses. Electrochemical studies like linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) demonstrates that the heterostructures deliver enhanced charge transfer kinetics. The Zn-Pc functionalized nanosheets display an overpotential of 233 mV for attaining a current density of 10 mA.cm-2 and the overpotential decreased to 165 mV after cycling due to the surface reconstruction, when the stability was assessed with chronoamperometry. Density Functional Theory (DFT) studies reveal that the charge transfer due to the adsorption of Zn-Pc onto WS2 nanosheets is comparatively better than that of Cu-Pc. This work recounts that by simple metal phthalocyanine functionalization, charge transfer characteristics of WS2 can be markedly improved, thereby signifying the importance of interface modification in two-dimensional (2D) heterostructures.

GIWAXS Characterization of Metal–Organic Framework Thin Films and Heterostructures: Quantifying Structure and Orientation

AbstractFor optoelectronic applications of metal–organic framework (MOF) thin films, it is important to be able to fabricate films and heterostructures that are highly oriented relative to the substrate's surface normal. However, process optimization to achieve this is difficult without sufficiently detailed structural characterization of the deposited films. It is demonstrated that 2D grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) data from a laboratory system go a long way to providing such characterization and can 1) better test structural models than 1D scans, 2) provide a quantitative estimate—useful for process optimization—of the fraction of the deposited film that has the desired surface‐oriented texture (2D powder), and 3) deliver such information as a function of depth into the film—useful for heterostructure characterization. Herein, GIWAXS data collection and analysis are introduced in the context of understanding MOF thin films, then it is shown how the desired oriented fraction (2D powder fraction) of UiO‐66 fabricated by vapor‐assisted conversion can be increased from 4% to over 95% by minimizing nucleation in solution. Finally, it is demonstrated that heterostructures of UiO‐66 and UiO‐67 can be grown wherein both layers are highly ordered (UiO‐66 83%, UiO‐67 >94%) once synthetic protocols are optimized.

Correlating Charge Transfer Dynamics with Interfacial Trap States in High-Efficiency Organic Solar Cells.

The charge transfer between the donor and acceptor determines the photogenerated carrier density in organic solar cells. However, a fundamental understanding regarding the charge transfer at donor/acceptor interfaces with high-density traps has not been fully addressed. Herein, a general correlation between trap densities and charge transfer dynamics is established by adopting a series of high-efficiency organic photovoltaic blends. It is found that the electron transfer rates are reduced with increased trap densities, while the hole transfer rates are independent of trap states. The local charges captured by traps can induce potential barrier formation around recombination centers, leading to the suppression of electron transfer. For the hole transfer process, the thermal energy provides a sufficient driving force, which ensures an efficient transfer rate. As a result, a 17.18% efficiency is obtained for PM6:BTP-eC9-based devices with the lowest interfacial trap densities. This work highlights the importance of interfacial traps in charge transfer processes and proposes an underlying insight into the charge transfer mechanism at nonideal interfaces in organic heterostructures.

A new strategy: realization of organic heteroepitaxy and organic alloys based on the similarity of CC and NN

The similarity of NN and CC in trans-4,4′-azobis(pyridine) and trans-1,2-bis(pyridin-4-yl)ethene offers an innovative approach for creating controllable and versatile organic heterostructure and organic alloy.

Molecular Engineering of Silicon Phthalocyanine to Improve the Charge Transport and Ammonia Sensing Properties of Organic Heterojunction Gas Sensors

AbstractNovel organic heterostructures fabricated with a bilayer consisting of an axially substituted silicon phthalocyanine (R2‐SiPc) derivative and lutetium bis‐phthalocyanine (LuPc2) are investigated for their ammonia sensing properties. Surface and microstructure characterization of the heterostructure films reveal either compact or highly porous surface topography in (345F)2‐SiPc and Cl2‐SiPc‐based heterostructures, while electrical characterization reveals a strong influence of the axial substituent in R2‐SiPc on NH3 sensing capabilities. Electrical characterization further demonstrates an apparent energy barrier for interfacial charge transport, which is higher in the (345F)2‐SiPc/LuPc2 heterojunction device. In‐depth charge transport studies by impedance spectroscopy further reveal a resistive interface in (345F)2‐SiPc/LuPc2 and faster bulk and interfacial charge transport in Cl2‐SiPc/LuPc2 heterojunction devices. Different interfacial charge transport capabilities and surface topographies affect NH3 sensing properties of the two heterojunction devices, in which (345F)2‐SiPc/LuPc2 reveals a fast and non‐linear response with a limit of detection (LOD) of 310 ppb, while Cl2‐SiPc/LuPc2 exhibits a slow, and linear response to NH3 with LOD of 100 ppb. Finally, different metrological parameters of the two sensors are correlated to the respective gas‐material interactions, in which adsorption and diffusion regimes are modulated by the surface topography and hydrophobicity of the sensing layer.

S-scheme MIL-101(Fe) octahedrons modified Bi2WO6 microspheres for photocatalytic decontamination of Cr(VI) and tetracycline hydrochloride: Synergistic insights, reaction pathways, and toxicity analysis

Solar-driven elimination of refractory contaminants is an ideal route to tackle the environmental issues. Nevertheless, the photocatalytic performance of photocatalysts is heavily restrained due to the insufficient accessible reactive sites and fast electrons/holes reunion. Herein, a novel metal–organic framework-based S-scheme heterostructure of MIL-101(Fe)/Bi2WO6 was synthesized by a simple solvothermal approach. The optimized MIL-101(Fe)/Bi2WO6 (MIL/BWO-2) affords the highest photo-activities under visible light, which are 13.7, 6.7 folds greater for Cr(VI) reduction, and 0.8, 10.5 folds higher for tetracycline hydrochloride oxidation compared with individual Bi2WO6 and MIL-101(Fe), respectively. The preeminent catalytic capability lies in two aspects: 1) the introduction of MIL-101(Fe) substantially enlarges the surface area of the composites, offering ample reaction sites and fostering pollutant adsorption and mass transportation; 2) the novel S-scheme photo-carrier transport mechanism assisted by oxygen vacancies favors spatial segregation and transport of photoinduced electrons/holes with superior redox capacity. Reactive species identification experiments verify that O2– and e– dominantly contribute to Cr(VI) reduction, while O2–, h+ and OH account for tetracycline hydrochloride destruction. Furthermore, the tetracycline photo-decomposition pathway, eco-toxicity evaluation, and photocatalytic mechanism were investigated comprehensively. This research paves the way for building high-performance MOFs-based S-scheme heterojunctions toward photocatalytic water purification.

Dynamic Epitaxial Growth of Organic Heterostructures for Polarized Exciton Conversion.

Highly spatial and angular precision in epitaxial-growth process is crucial for constructing organic low-dimensional heterostructures (OLDHs) with the desired substructures, which remains significant challenge owing to the unpredicted location of complex heterogeneous nucleation. Herein, a dynamic epitaxial-growth approach is developed along the tailored longitudinal/horizontal directions to create diverse OLDHs with hierarchical architectures. The controlled morphology evolution of seed crystals from kinetic to thermodynamic species is achieved via incrementally increasing the crystallization time from 0 to 600s. Accordingly, the kinetic and thermodynamic seed crystals respectively present the specific lattice-matching crystal-planes of (100) and (011), which facilitates the longitudinal epitaxial-growth (LG) process for triblock heterostructures, and the horizontal epitaxial-growth (HG) process for axial-branch heterostructures. The dominant core/shell heterostructures are prepared via both LG and HG processes with a crystallization time of ≈30s. Significantly, these prepared OLDHs realize the rationally polarized exciton conversion for optical logic gate application through the exciton conversion and photon propagation at the heterojunction. This strategy provides an avenue for the precise synthesis of OLDHs with anisotropy optical characters for integrated optoelectronics.

Deposition and Characterization of Heterostructures Based on Doped Ferrocene for Film-Device Applications

Novel heterostructures based on ferrocenium hexafluorophosphate (FcPF6), 2,6-dihydroxyanthraquinone (DHAQ) or 2,6-diaminoanthraquinone (DAAQ), zinc phthalocyanine (ZnPc) and nylon 11 were deposited by the high-vacuum thermal evaporation (HVTE) technique. Morphological and mechanical characterizations of these organic heterostructures FcPF6:DHAQ/nylon(ZnPc) and FcPF6:DAAQ/nylon(ZnPc) were carried out. Subsequently, corresponding optical parameters were calculated. The heterostructure with FcPF6:DHAQ presented the lowest optical band gap and fundamental band gap at 1.55 eV and 2.45 eV, respectively. The nylon(ZnPc) layer favors the optical behavior and places these heterostructures within organic low-bandgap semiconductor range. Additionally, devices were fabricated, and their electrical behavior was evaluated. The ITO/FcPF6:DHAQ/nylon(ZnPc)/Ag device exhibits ohmic behavior, and the ITO/FcPF6:DAAQ/nylon(ZnPc)/Ag device exhibits ohmic behavior at low voltages, but at V ≥ 5 V, its behavior changes to Space Charge Limited Current (SCLC). This device carries a maximum current of 0.02 A, three orders of magnitude higher than the current carried by the device with the DHAQ. The SCLC conduction mechanism showed a hole mobility of 9.27 × 10−8 (cm2)/Vs, the concentration of thermally excited holes of 3.01 × 1023 m−3, and trap concentration of 3.93 × 1021 m−3. FcPF6:DHAQ/nylon(ZnPc) and FcPF6:DAAQ/nylon(ZnPc) are potential candidates for organic devices as an emitter layer and active layer, respectively.

Effect of Aluminum Nanostructured Electrode on the Properties of Bulk Heterojunction Based Heterostructures for Electronics

The properties of organic heterostructures with mixed layers made of arylenevinylene-based polymer donor and non-fullerene perylene diimide acceptor, deposited using Matrix Assisted Pulsed Laser Evaporation on flat Al and nano-patterned Al electrodes, were investigated. The Al layer electrode deposited on the 2D array of cylindrical nanostructures with a periodicity of 1.1 µm, developed in a polymeric layer using UV-Nanoimprint Lithography, is characterized by an inflorescence-like morphology. The effect of the nanostructuring on the optical and electrical properties was studied by comparison with those of the heterostructures based on a mixed layer with fullerene derivative acceptor. The low roughness of the mixed layer deposited on flat Al was associated with high reflectance. The nano-patterning, which was preserved in the mixed layer, determining the light trapping by multiple scattering, correlated with the high roughness and led to lower reflectance. A decrease was also revealed in photoluminescence emission both at UV and Vis excitation of the mixed layer, with the non-fullerene acceptor deposited on nano-patterned Al. An injector contact behavior was highlighted for all Al/mixed layer/ITO heterostructures by I-V characteristics in dark. The current increased, independently of acceptor (fullerene or non-fullerene), in the heterostructures with nano-patterned Al electrodes for shorter conjugation length polymer donors.

Wavelength and Polarization Sensitive Synaptic Phototransistor Based on Organic n-type Semiconductor/Supramolecular J-Aggregate Heterostructure.

Human retina- and brain-inspired optoelectronic synapses, which integrate light detection and signal memory functions for data processing, have significant interest because of their potential applications for artificial vision technology. In nature, many animals such as mantis shrimp use polarized light information as well as scalar information including wavelength and intensity; however, a spectropolarimetric organic optoelectronic synapse has been seldom investigated. Herein, we report an organic synaptic phototransistor, consisting of a charge trapping liquid-crystalline perylene bisimide J-aggregate and a charge transporting crystalline dichlorinated naphthalene diimide, that can detect both wavelength and polarization information. The device shows persistent positive and negative photocurrents under low and high voltage conditions, respectively. Furthermore, the aligned organic heterostructure in the thin-film enables linearly polarized light to be absorbed with a dichroic ratio of 1.4 and 3.7 under transverse polarized blue and red light illumination, respectively. These features allow polarized light sensitive postsynaptic functions in the device. Consequently, a simple polarization imaging sensor array is successfully demonstrated using photonic synapses, which suggests that a supramolecular material is an important candidate for the development of spectropolarimetric neuromorphic vision systems.

Directed self-assembly of organic crystals into chip-like heterostructures for signal processing

Organic single crystals show broad application prospects in the field of optical confinement and waveguides due to their low optical transmission loss and tunable optical properties. Individual one- or two-dimensional (1D or 2D) optical waveguide crystals have the limitations of a single function in organic photonics. In this work, a chip-like organic heterostructure was fabricated using an elaborately designed, sequential growth method. By regulating the concentration of each organic component, the processes of solution self-assembly, etching, and epitaxial self-assembly are successively performed to complete the directional growth of organic micro/nanostructures. Notably, the as-prepared chip-like organic heterostructure is composed of 1D/2D optical waveguide crystals, which can realize multidimensional photon transportation and multi-terminal directional optical signal output. Furthermore, the unique 2D optical waveguide properties of the chip-like heterostructures offer opportunities for constructing the encoding form of the output optical signal at the micro/nanoscale.