Organic-inorganic Heterostructures Research Articles

Carbon Nanotube-Quantum Dot Nanohybrids: Coupling with Single-Particle Control in Aqueous Solution.

A strategy is reported for the controlled assembly of organic-inorganic heterostructures consisting of individual single-walled carbon nanotubes (SWCNTs) selectively coupled to single semiconductor quantum dots (QDs). The assembly in aqueous solution was controlled towards the formation of monofunctionalized SWCNT-QD structures. Photoluminescence studies in solution, and on surfaces at the single nanohybrid level, showed evidence of electronic coupling between the two nanostructures. The ability to covalently couple heterostructures with single particle control is crucial for the design of novel QD-based optoelectronic and light-energy conversion devices.

Molecular Alignment and Electronic Structure of N,N'-Dibutyl-3,4,9,10-perylene-tetracarboxylic-diimide Molecules on MoS2 Surfaces.

The molecular orientation of organic semiconductors on a solid surface could be an indispensable factor to determine the electrical performance of organic-based devices. Despite its fundamental prominence, a clear description of the emergent two-dimensional layered material-organic interface is not fully understood yet. In this study, we reveal the molecular alignment and electronic structure of thermally deposited N,N'-dibutyl-3,4,9,10-perylene-dicarboximide (PTCDI-C4) molecules on natural molybdenum disulfide (MoS2) using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The average tilt angle determination reveals that the anisotropy in the π* symmetry transition of the carbon K-edge (284-288 eV range) is present at the sub-monolayer regime. Supported by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and resonant photoemission spectroscopy (RPES) measurements, we find that our spectroscopic measurements indicate a weak charge transfer established at the PTCDI-C4/MoS2 interface. Sterical hindrance due to the C4 alkyl chain caused tilting of the molecular plane at the initial thin film deposition. Our result shows a tunable interfacial alignment of organic molecules on transition metal dichalcogenide surfaces effectively enhancing the electronic properties of hybrid organic-inorganic heterostructure devices.

Ultrafast Charge Transfer and Enhanced Absorption in MoS2-Organic van der Waals Heterojunctions Using Plasmonic Metasurfaces.

Hybrid organic-inorganic heterostructures are attracting tremendous attention for optoelectronic applications due to their low-cost processing and high performance in devices. In particular, van der Waals p-n heterojunctions formed between inorganic two-dimensional (2D) materials and organic semiconductors are of interest due to the quantum confinement effects of 2D materials and the synthetic control of the physical properties of organic semiconductors, enabling a high degree of tunable optoelectronic properties for the heterostructure. However, for photovoltaic applications, hybrid 2D-organic heterojunctions have demonstrated low power conversion efficiencies due to the limited absorption from constraints on the physical thickness of each layer. Here, we investigate the ultrafast charge transfer dynamics between an organic polymer:fullerene blend and 2D n-type MoS2 using transient pump-probe reflectometry. We employ plasmonic metasurfaces to enhance the absorption and charge photogeneration within the physically thin hybrid MoS2-organic heterojunction. For the hybrid MoS2-organic heterojunction in the presence of the plasmonic metasurface, the charge generation within the polymer is enhanced 6-fold, and the total active layer absorption bandwidth is increased by 90 nm relative to the polymer:fullerene blend alone. We demonstrate that MoS2-organic heterojunctions can serve as hybrid solar cells, and their efficiencies can be improved using plasmonic metasurfaces.

Nanoscale Strategies for Light Harvesting.

Recent advances and the current status of challenging light-harvesting nanomaterials, such as semiconducting quantum dots (QDs), metal nanoparticles, semiconductor-metal heterostructures, π-conjugated semiconductor nanoparticles, organic-inorganic heterostructures, and porphyrin-based nanostructures, have been highlighted in this review. The significance of size-, shape-, and composition-dependent exciton decay dynamics and photoinduced energy transfer of QDs is addressed. A fundamental knowledge of these photophysical processes is crucial for the development of efficient light-harvesting systems, like photocatalytic and photovoltaic ones. Again, we have pointed out the impact of the metal-nanoparticle-based surface energy transfer process for developing light-harvesting systems. On the other hand, metal-semiconductor hybrid nanostructures are found to be very promising for photonic applications due to their exciton-plasmon interactions. Potential light-harvesting systems based on dye-doped π-conjugated semiconductor polymer nanoparticles and self-assembled structures of π-conjugated polymer are highlighted. We also discuss the significance of porphyrin-based nanostructures for potential light-harvesting systems. Finally, the future perspective of this research field is given.

Organic–inorganic nanostructures for luminescent indication in the near-infrared range

Amplifying and quenching of IR luminescence of colloidal Ag2S quantum dots were revealed to take place when they couple to organic dye molecules of 3,3′-di-(γ-sulfopropyl)-9-ethyl-4,5,4′,5′-dibenzothiacarbocyanine betaine and erytrosine pyridinium salts, respectively. The observed effects are explained as due to the formation of organic–inorganic heterostructures with different mutual arrangement of electronic states of the dyes and the quantum dots.

Visible/near-IR-light-driven TNFePc/BiOCl organic–inorganic heterostructures with enhanced photocatalytic activity

Although semiconductor photocatalysis has been reported for more than 40 years, the spectral response is still focused on the region of UV-Visible and it is seldom extended to more than 600 nm. In this work, visible/near-IR-light-driven 2,9,16,23-tetranitrophthalocyanine iron (FeTNPc)/bismuth oxychloride (BiOCl) organic-inorganic heterostructures have been synthesized by a two-step solvothermal method. The obtained products were characterized by X-ray diffraction, Fourier transform infrared spectra, scanning electron and transmission microscopy, energy dispersive X-ray spectrometer, UV-vis diffuse reflectance spectroscopy, nitrogen adsorption-desorption, and electrochemical measurements. The photocatalytic activity for the decomposition of methyl orange and bisphenol A solution can be significantly improved under visible/near-IR-light irradiation. Through detecting the main oxidative species by trapping experiments, the results show holes and ˙O2(-) radicals are majorly and minorly responsible for photodegradation respectively. What's more, the FeTNPc/BiOCl composite photocatalyst still retained the photocatalytic activity after three cycle measurements.

Van der Waals p–n Junction Based on an Organic–Inorganic Heterostructure

Organic–inorganic heterostructures are an emerging topic that is very interesting for optoelectronics. Here, non‐conventional p–n junctions are investigated using organic rubrene single crystal and 2D MoS2 as the p‐ and n‐type semiconducting materials, respectively. The current‐rectifying behavior is clearly observed in the junction device. The rectification ratio can be electrically tuned by the gate voltage due to the 2D nature of the heterostructure. The devices also show good photoresponse properties with a photoresponsivity of ≈500 mA W−1 and a fast response time. These findings suggest a new route to facilitate the design of nanoelectronic and optoelectronic devices based on layered inorganics and organics.

Improved opto-electrical behavior of ZnO/C60 core/shell type organic–inorganic heterostructure

We report a successful synthesis of ZnO/C60 core/shell-type organic–inorganic hybrid nanorod arrays (NRAs) using simple chemical route. X-ray diffraction pattern (XRD) reveals hexagonal crystal structure of ZnO along with the face-centered cubic (fcc) structure of C60. Detailed Fourier transform infrared spectroscopy (FTIR) inferred the attachment of C60 on the surface of ZnO NRAs. HRTEM observation confirmed ∼3nm thickness of a very thin C60 nanocrystals shell layer formation. HRSEM image shows the existence of C60 on vertically aligned ZnO NRAs. UV–visible absorption spectra have two absorption edges corresponding to the energy band gap values of 3.05 and 1.83eV which arise due to core ZnO and shell C60 respectively. Photoluminescence spectra reveal a strong enhancement in the NBE emission and suppression in the deep-level emission on the surface modified ZnO NRAs. The measured electrical resistivity under illumination for ZnO/C60 core/shell is lower than that of bare ZnO NRAs.

High-efficiency hybrid solar cells by nanostructural modification in PEDOT:PSS with co-solvent addition

Conducting polymer poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) is gaining technological importance for the fabrication of organic and organic–inorganic heterostructure devices. The conductivity of PEDOT:PSS can be improved by the addition of co-solvents. Here, we show that the simple addition of a suitable wt% of a co-solvent, either ethylene glycol (EG) or dimethyl sulfoxide (DMSO), in PEDOT:PSS can significantly enhance the performance of hybrid solar cells. We provide a morphological model to explain the influence of the co-solvents in PEDOT:PSS, in which the co-solvent modifies the internal crystalline ordering of individual PEDOT nanocrystals that increases the crystal size and forms closely packed nanocrystals, and it also facilitates rearrangement of PSS that reduces its surface chain networks to enhance the polymer conductivity and hybrid solar cell properties. A hybrid solar cell made of EG 7 wt% modified PEDOT:PSS on planar Si exhibits an exceptionally high power conversion efficiency exceeding 12% for the first time.

Controllable Growth of Conducting Polymers Shell for Constructing High-Quality Organic/Inorganic Core/Shell Nanostructures and Their Optical-Electrochemical Properties

High-quality metal oxide/conducting polymer (CP) heterostructured nanoarrays are fabricated by controllable electrochemical polymerization of CP shells on preformed metal oxides nanostructures for both electrochromic and electrochemical energy storage applications. Coaxial and branched CP shells can be obtained on different backbones (nanowire, nanorod, and nanoflake) simply by controlling the electrodeposition time. "Solvophobic" and "electrostatic" interactions are proposed to account for the preferential growth of CP along metal oxides to form core/shell heterostructures. The coaxial TiO2/polyaniline core/shell nanorod arrays exhibit remarkable electrochromic performance with rich color changes, fast optical modulation, and superior cycling stability. In addition, the Co3O4/polyaniline core/shell nanowire arrays are evaluated as an anode material of Li ion battery and exhibit enhanced electrochemical property with higher and more stable capacity than the bare Co3O4 nanowires electrode. These unique organic-inorganic heterostructures with synergy pave the way for developing new functional materials with enhanced properties or new applications.

Electrochemically assembled planar hybrid poly(3-methylthiophene)/ZnO nanostructured composites

Step by step electrochemical assembling layers of compact ZnO (ZnOcomp), ZnO nanorods (ZnONR) and poly(3-methylthiophene) (P3MT) has been applied to form the photovoltaically active hybrid organic–inorganic heterostructure. Photoluminescence and photoconductivity characterization of the synthesized ZnOcomp and ZnONR layers display their different defect and doping states resulting in a non-linear I–V behavior of the assembled complex ZnOcomp/ZnONR layer structure for account of formation of a p–n junction at the interface. We find some healing of the defect states at surface of the ZnOcomp layer after its covering with ZnONR layer. The photoelectrochemical deposition of the stable P3MT on surface of the complex ZnOcomp/ZnONR structure is realized under light irradiation with wavelength close to near-band-edge (NBE) emission of ZnO (∼380nm) when using the special mixed voltammetry–potentiostatic–galvanostatic mode. This mode is found to minimize overoxidation/degradation of the forming P3MT. After the synthesis the formed P3MT layer is electrochemically reduced to move it to a semiconductor state. The resulting hybrid ZnOcomp/ZnONR/P3MT heterostructure is photovoltaically active and displays open-circuit voltage about 0.45V.

White Light Electroluminescence by Organic-Inorganic Heterostructures with CdSe Quantum Dots as Red Light Emitters

We have developed a white organic light-emitting diode featuring a double emission layer comprising a blue light-emitting conductive polymer as a host material for Cadmium Selenide (CdSe) quantum dots as red light emitters and tris-(8-hydroxyquinoline) aluminium thin layer for green light emission. The Commission Internationale de l'Eclairage coordinates of the emitting light of the device were found to be (0.32, 0.40) which were only slightly changed over a range of applied voltages between 5 and 10 volts. The use of CdSe nanocrystalline quantum dots (surface-stabilized with hexadecylamine/trioctylphosphine oxide ligands) in the hybrid heterostructure with poly(9,9-di-n-octylfluorenyl-2,7-diyl) conductive polymer was studied for a variety of CdSe concentrations developing the performance of the device in means of overcoming segregation problems in the blend. Besides, constituents' ratio was further examined for the exploration of possible energy transfer from polymer host material to the CdSe quantum dots as a key factor for well-balanced emission in the electroluminescent devices.

Electrical Spin Injection from an Organic-Based Ferrimagnet in a Hybrid Organic-Inorganic Heterostructure

We report the successful extraction of spin-polarized current from the organic-based room temperature ferrimagnetic semiconductor V[TCNE](x) (x∼2, TCNE: tetracyanoethylene; T(C)∼400 K, E(G)∼0.5 eV, σ(300 K)∼10(-2) S/cm) and its subsequent injection into a GaAs/AlGaAs light-emitting diode. The spin current tracks the magnetization of V[TCNE](x∼2), is weakly temperature dependent, and exhibits heavy-hole-light-hole asymmetry. This result has implications for room temperature spintronics and the use of inorganic materials to probe spin physics in organic and molecular systems.

A photovoltaic response of a Schottky diode based on the conducting polymer PEDOT:PSS and inorganic semiconductors

Hybrid organic-inorganic heterostructures have been produced using the conducting polymer PEDOT:PSS and three types of semiconductor single crystals, i.e., high-ohmic and low-ohmic cadmium sulphide (CdS, n-type semiconductor) and low-ohmic cadmium telluride (CdTe, p-type semiconductor). A photovoltaic (PV) response was observed upon light illumination of both CdS/PEDOT:PSS and CdTe/PEDOT:PSS heterojunctions. Photocurrent spectra unequivocally evidenced the main contribution of band-band transitions of inorganic crystals to the PV response, and current-voltage measurements indicated that band bending due to a depleting region at the surface of the crystals takes place. The suggested band bending was consistent with the model of the vacuum level alignment only at the interface of the low-ohmic CdS crystal and the polymer, which results in formation of a Schottky barrier responsible for the PV response. However, the analogous band bending for high-ohmic CdS and p-type CdTe crystals could be associated only with the Fermi level pinning regime at the semiconductor interfaces.

Nonradiative exciton energy transfer in hybrid organic-inorganic heterostructures

Nonradiative energy transfer from a GaAs quantum well to a thin overlayer of an infrared organic semiconductor dye is unambiguously demonstrated. The dynamics of exciton transfer are studied in the time domain by using pump-probe spectroscopy at the donor site and fluorescence spectroscopy at the acceptor site. The effect is observed as simultaneous increase in the population decay rate at the donor and of the rise time of optical emission at the acceptor sites. The hybrid configuration under investigation provides an alternative nonradiative, noncontact pumping route to electrical carrier injection that overcomes the losses imposed by the associated low carrier mobility of organic emitters.

Improvement of rare-earth complex electroluminescence by using organic–inorganic heterostructure

A new organic–inorganic heterostructure device was designed. The wide gap semiconductor ZnS was acted as an electron transporting, electron acceleration and hole blocking layer. The combined structure of organic/inorganic device has three distinguished advantages: (i) avoid these uncontrolled phenomena on organic material interfaces; (ii) increase the energy and number of injected electrons into ploy ( N-vinyl-carbazole) PVK (iii) enhance hole-current density by the increase of the electric field strength in PVK due to a high dielectric constant material ZnS as an electron transporting layer. Characteristic emissions of complex of terbium ion with o-benzoylbenzoate ion and 1, 10-phenathroline (Tb(o-BBA) 3(phen)) based on organic–inorganic heterostructure device were obtained. The maximum EL intensity was improved more than three times and reached to 326 cdm −2 compared with the pure organic electroluminescence device.

Electroluminescence of Tb( o-BBA) 3(phen) based on an organic–inorganic heterostructure

An organic–inorganic heterostructure device was designed to improve the electroluminescence intensity of terbium ion. In this heterostructure, a mixed solution of (Tb( o-BBA) 3(phen)) and poly( N-vinylcarbazole) (PVK) was prepared with a weight ratio of 3:1 which was acted as a hole transporting and emitting layer. A wide band semiconductor zinc sulfide (ZnS) layer was used as an electron transporting and hole blocking layer. Characteristic emissions of terbium ion from the organic–inorganic heterostructure device were observed and the electroluminescence intensity of terbium ion increased abruptly when the driving voltage went beyond 20.5 V. This may be due to a directly impact excitation of terbium ion by hot electrons, accelerated in ZnS layer, and then a recombination with the injected holes. The electroluminescence mechanism of Tb( o-BBA) 3(phen)-doped PVK was the charge-carrier trapping process by the dopant molecule according to the emission spectra of PVK and the excitation spectra of Tb( o-BBA) 3(phen).

Influences of organic hole-transport layer on the emission of organic–inorganic heterostructure devices

In this paper, influences of poly ( N-vinyl-carbazole) (PVK) on the emission properties of zinc selenide (ZnSe)-based organic–inorganic heterostructure devices have been studied. A broad band emission peak at 443 nm, with shoulders at 520 and 595 nm, was observed from ITO/PVK(80 nm)/ZnSe(120 nm)/Alq 3(15 nm)/Al under electric fields and it consisted of emissions from PVK, ZnSe and Alq 3 layers. Therefore, a charge carrier injection luminescence in ZnSe layer is suggested. By changing the thickness of PVK layer and/or ZnSe layer, the roles of PVK in the device were discussed.

White light emission from organic–inorganic hererostructure devices by using CdSe quantum dots as emitting layer

In this paper, white light emission was obtained from organic–inorganic heterostructure devices by using CdSe quantum dots as emitting layer, in which CdSe quantum dots were synthesized via a colloidal chemical approach by using CdO and Se powder as precursors. Photoluminescence of CdSe quantum dots demonstrated a white emission with a full wavelength at half maximum (FWHM) of about 200 nm under ambient conditions, and the white emission could be observed in both multilayer device ITO/PEDOT:PSS/CdSe/BCP/Alq 3/Al and single-layer device: ITO/PEDOT:PSS/CdSe/Al. The broad emission was attributed to the inhomogeneous broadening. The CIE coordinates of the multilayer device were x=0.35 and y=0.40. The white-light-emitting diodes with CdSe quantum dots as the emitting layer are potentially useful in lighting applications.

ZnSe-based organic-inorganic heterostructure diodes

ZnSe-based organic-inorganic heterostructure diodes in which ZnSe layer was fabricated by electron-beam evaporation were studied. Electroluminescence from ZnSe peaking at 578nm was observed from bilayer device ITO/ZnSe(50nm)/Alq3(12nm)/Al, but it is difficult to observe any EL emission from single-layer diode ITO/ZnSe(50—120nm)/Al. Based on this, we further introduced a PVK or NPB hole-transporting layer (HTL), to make trilayer devices ITO/HTL/ZnSe/Alq3/Al to investigate the influence of ZnSe layer on the emission of the trilayer devices by varying the device structure. Our experimental data of EL emission confirm the roles played by ZnSe in these devices of transporting not only electrons but also holes, as well as acting as an emissive layer. Furthermore, a luminescence mechanism of charge carriers injection luminescence in ZnSe layer is suggested.