Organic Rubrene Research Articles

Investigation of high-detectivity self-powered photodetectors of Rubrene/Bi2Se3 hybrid Van der Waals heterojunction

This paper investigates the Vander Waals heterostructure of organic rubrene and topological insulator Bi2Se3 with an atomically abrupt interface with exciting applications in electronic and optoelectronic devices. This organic/inorganic heterostructure (OIH) was prepared using a simple two-step physical vapor deposition process; based on this hybrid structure, a self-powered photodetector was then constructed. The Dirac surface state at the heterointerface enhances the splitting and transferring of photo-generated carriers, resulting in improved device characteristics. Under 1064 nm, the prepared photodetectors demonstrated a maximum responsivity (6.37 A/W), a high detectivity (3.42 × 1010 Jones), and ultrafast photoresponse speeds with rise time (1.17 µs) and decay time (1.59 µs), respectively. These promising results suggest that these PDs can be used in various photodetection applications and may lead to developing new devices.

Unveiling the Doping- and Temperature-Dependent Properties of Organic Semiconductor Orthorhombic Rubrene from First Principles

Due to its large hole mobility, organic rubrene (C42H28) has attracted research questions regarding its applications in electronic devices. In this work, extensive first-principles calculations are performed to predict some temperature- and doping-dependent properties of organic semiconductor rubrene. We use density functional theory (DFT) to investigate the electronic structure, elastic and transport properties of the orthorhombic phase of the rubrene compound. The calculated band structure shows that the orthorhombic phase has a direct bandgap of 1.26 eV. From the Vickers hardness (1.080 GPa), our calculations show that orthorhombic rubrene is not a super hard material and can find useful application as a flexible semiconductor. The calculated transport inverse effective mass and electronic fitness function show that the orthorhombic rubrene crystal structure is a p-type thermoelectric material at high temperatures.

Waterproof and Flexible Perovskite Photodetector Enabled By P-type Organic Molecular Rubrene with High Moisture and Mechanical Stability.

Metal halide perovskite films have gained significant attention because of their remarkable optoelectronic performances. However, their poor stability upon the severe environment appears to be one of the main facets that impedes their further commercial applications. Herein, a method to improve the stability of flexible photodetectors under water and humidity environment without encapsulation is reported. The devices are fabricated using the physical vapor deposition method (Pulse Laser Deposition & Thermal Evaporation) under high-vacuum conditions. An amorphous organic Rubrene film with low molecular polarity and high elastic modulus serves as both a protective layer and hole transport layer. After immersed in water for 6000min, the photoluminescence intensity attenuation of films only decreased by a maximum of 10%. The demonstrator device, based on Rubrene/CsPbBr3/ZnO heterojunction confirms that the strategy not only enhances device moisture and mechanical stability but also achieves high sensitivity in optoelectronic detection. In self-powered mode, it has a fast response time of 79.4 µs /207.6 µs and a responsivity 124mAW-1. Additionally, the absence of encapsulation simplifies the fabrication of complex electrodes, making it suitable for various applications. This study highlights the potential use of amorphous organic films in improving the stability of perovskite-based flexible devices.

Spontaneously homogeneous alignment of liquid crystals on self-assembly organic rubrene

A novel spontaneously homogeneous liquid crystal (LC) alignment with self-assembled organic rubrene layer on the substrate surface has been reported. The spontaneous alignment technique without surface pre-treatment results in low cost, short processing time, and the room-temperature processing extends application to plastic device. The rubrene-nematic LC mixture is used to fabricate the LC cell. During the capillary filling, the LC molecules align in the flow direction. Meanwhile, the flow-induced LC alignment enforces the tetracene of the rubrene dopants along the flow direction because of the van der Waals and π–π interactions between the rubrene and LC molecules. Afterwards, the rubrene dopants spontaneously migrate onto substrate surface and self-assemble as the triclinic crystalline rubrene (TCR) with ribbon morphology. The LC alignment on TCR has a low pretilt angle, thereby providing a homogeneous LC alignment spontaneously. LC alignment on TCR shows a higher thermal stability compared to conventional polyimide due to the strong interactions of the rubrene and LC molecules. Moreover, the rubrene molecules remain in the bulk suppress the free-ions, decrease the rotational viscosity of LCs and hence shortening the response time of cell. The suppressed free-ions also decrease the screening effect on the substrate surfaces and hence the operation voltage of cell. The TCR structure on the substrate surface and the residual rubrene molecules dispersed in the bulk simultaneously contribute to the enhancement in electro-optical performance of the LC cell.

Organic bipolar transistors

Devices made using thin-film semiconductors have attracted much interest recently owing to new application possibilities. Among materials systems suitable for thin-film electronics, organic semiconductors are of particular interest; their low cost, biocompatible carbon-based materials and deposition by simple techniques such as evaporation or printing enable organic semiconductor devices to be used for ubiquitous electronics, such as those used on or in the human body or on clothing and packages1–3. The potential of organic electronics can be leveraged only if the performance of organic transistors is improved markedly. Here we present organic bipolar transistors with outstanding device performance: a previously undescribed vertical architecture and highly crystalline organic rubrene thin films yield devices with high differential amplification (more than 100) and superior high-frequency performance over conventional devices. These bipolar transistors also give insight into the minority carrier diffusion length—a key parameter in organic semiconductors. Our results open the door to new device concepts of high-performance organic electronics with ever faster switching speeds.

Molecular crystallization of rubrene thin films assisted by gold nanoparticles

We demonstrate that crystalline organic rubrene thin films can be obtained by a facile spin-coating method using gold (Au) nanoparticles (NPs). Dodecanethiol-functionalized Au NPs were dissolved with rubrene molecules in solvent and a thin film of Au/rubrene was prepared by a simple spin coating process. The results of confocal photoluminescence (PL) and absorption spectral mapping confirmed the local formation of orthorhombic crystalline structures of the Au/rubrene hybrid film, in contrast to the monoclinic structure of plain rubrene films. Further, the results of transmission electron microscopy (TEM) and X-ray diffraction analysis, as well as Raman spectroscopy measurements of the rubrene and Au/rubrene films suggested the formation of high crystalline Au/rubrene film. The molecular crystallization of the Au/rubrene hybrid film is attributed to the nucleation effect of the Au NPs.

High-performance self-powered photodetector based on organic/inorganic hybrid van der Waals heterojunction of rubrene/silicon* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11604228, 11774208, and 11974222), the Science and Technology Planning Foundation of Shandong Province, China (Grant No. J18KA219).

Organic/inorganic hybrid van der Waals heterostructure with an atomically abrupt interface has attracted great research interests within the field of multifunctional electronic and optoelectronic devices. The integration of organic rubrene films with inorganic Si semiconductors can avoid the atomic mutual-diffusion at the interface, and provide the possibility of forming two-dimensional van der Waals heterojunction accompanied with the type-II energy band alignment, due to the transfer behaviors of majority carriers at the interface. In this study, the high-quality rubrene/Si van der Waals heterostructure with an electronically abrupt junction was prepared, and a self-powered photodetector was then constructed based on this hybrid heterojunction. The photodetector demonstrated an excellent switching response to the 1064 nm monochromatic light with large on/off current ratio of 7.0 × 103, the maximum photocurrent of 14.62 mA, the maximum responsivity of 2.07 A/W, the maximum detectivity of 2.9 × 1011 Jones, and a fast response time of 13.0 μs. This study offers important guidance for preparing high-quality rubrene/Si hybrid van der Waals heterostructure with desirable band alignment, and the designed heterojunction photodetector has an important application prospect in the field of multifunctional optoelectronics.

Enhanced blue photoluminescence and new crystallinity of Ag/organic rubrene core-shell nanoparticles through hydrothermal treatment

Light-emitting organic semiconductors have attracted considerable attention for the nanoscale fabrication of organic-based displays and their potential application in optoelectronics, plasmonics, and photonics. In this study, core-shell hybrid nanostructures of organic rubrene coated on Ag nanoparticles (NPs) have been synthesized using a chemical reduction method. The thickness of the rubrene shell was 2.6–6.0 nm and the diameter of the Ag core was 30–70 nm. The optical and structural properties of the Ag/rubrene core-shell NPs were tuned by hydrothermal (HT) treatment at 190 °C. The Ag/rubrene core-shell NPs were characterized by high-resolution transmission electron microscopy and energy-dispersive X-ray (EDX) spectroscopy before and after the HT treatment, and their structural properties were confirmed through X-ray diffraction (XRD) analysis. XRD peaks related to an orthorhombic phase were observed along with the original triclinic crystal structure of the rubrene shell, and the triclinic crystal domain size increased from 28.2 nm to 30.8 nm owing to the HT treatment. Interestingly, the green light emission (λem = 550 nm) of the Ag/rubrene core-shell NPs changed to blue light emission (λem = 425 nm), increasing in intensity through the HT treatment. This is caused by the crystal change with H-type aggregation and enhanced energy transfer from a surface plasmon resonance.

Energy and charge transfer effects for hybrids of perovskite CsPbBr3 quantum dots on organic semiconducting rubrene nanosheet

Abstract Functionalized perovskite CsPbBr3 quantum dots (CsPbBr3-QDs) were loaded on the surface of a p-type organic rubrene (5,6,11,12-tetraphenyltetracene) nanosheet (NS) for the fabrication of a new hybrid nano-system. Using a high–resolution laser confocal microscope, the nanoscale photoluminescence (PL) characteristics of the CsPbBr3-QDs/rubrene-NS hybrids were investigated. We observed a significant enhancement of the PL intensity of the rubrene-NS after the hybridization with the CsPbBr3-QDs, which originated from the fluorescence resonance energy transfer from the CsPbBr3-QDs to the rubrene-NS. The PL enhancement ratio varied according to the density of the QDs on the NS. To investigate the hybridization effect with CsPbBr3-QDs on the electrical characteristics of the rubrene-NS, we fabricated field-effect transistors (FETs) using the pristine and hybrid samples as an active layer. The currents of both FETs using the pristine rubrene-NS and hybrid QDs/rubrene-NS increased with light irradiation through the contribution of photo-excited charges. After the hybridization with the CsPbBr3-QDs on the rubrene channel, both the electrical current and mobility decreased compared with the pristine rubrene-based FET. This can be explained by the relative decrease of hole concentration in the active channel region near dielectric layer through the interfacial charge transfer between the QDs and the NS, as well as the de-doping effect of the QDs on the rubrene-NS. Thus, we observed the energy and charge transfer effects for the CsPbBr3-QDs/rubrene-NS hybrids, which can be applied to advanced nanoscale photonics and optoelectronics.

Enhanced Local and Nonlocal Photoluminescence of Organic Rubrene Microrods using Surface Plasmon of Gold Nanoparticles: Applications to Ultrasensitive and Remote Biosensing

Nonlocal photoluminescence (PL) signal transfer through semiconducting nanostructures has been intensively studied for its potential applicability in photonic circuits, optical communications, and optical sensing. In this study, organic semiconducting rubrene microrods (MRs) were synthesized and hybridized with functionalized gold nanoparticles (Au-NPs) to optimize both their optical and biosensing properties. The steady-state local PL intensity of the rubrene MR was considerably enhanced by the Au-NPs’ hybridization due to the energy-transfer effect from the surface plasmon (SP) coupling. It was clearly observed that the nonlocal PL signal-transfer efficiency of rubrene/Au-NPs hybrid MRs drastically increased along crystalline axes with the aid of the SP effect. The coupling of exciton polaritons in the luminescent rubrene MR with the SP as well as the scattering effect contribute to the variation of the exciton decay rate, resulting in a change in the PL signal-transfer efficiency for the hybrid MRs. Th...

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.

Electrically controlled photoluminescence efficiency of organic rubrene microplates

Semiconducting organic rubrene (5,6,11,12-tetraphenyltetracene) microplates (MPs) were fabricated using physical vapor transport to study tunable photoluminescence (PL) characteristics through an applied electric field. The nanoscale PL intensities of a rubrene MP, which were measured via high-resolution laser confocal microscopy (LCM), clearly depended on the applied electric field intensity. The LCM PL intensity of the rubrene MP sinusoidally varied with the periodic change of the electric field. We also observed the aging effect on the LCM PL intensity of rubrene MPs. Control of the charge dissociation rate of photoinduced excitons by the external electric field can be the cause of the tunable PL efficiency of the MP.

Fine Control of Photoluminescence and Optical Waveguiding Characteristics of Organic Rubrene Nanorods Using Focused Electron-Beam Irradiation

We demonstrate the fine control of the nanoscale photoluminescence (PL) and optical waveguiding characteristics of light-emitting organic rubrene nanorods (NRs) through focused electron-beam (E-beam) irradiation. Nanoscale laser confocal microscope PL intensity and spectra of the focused E-beam-treated compartments of the rubrene NR drastically varied with E-beam dose, and yellow-white light emission from those compartments with a specific E-beam dose was observed. In optical waveguiding experiments, the propagation characteristics of optical signals along the single NR were dependent on the crystalline structure of the rubrene. For the E-beam treated NR, the waveguiding PL signals along the crystalline a-axis had relatively higher output, indicating the major axis for the optical energy transfer. Additionally, the waveguiding characteristics such as decay constant along the crystalline b-axis and c-axis of the NR considerably varied at the boundary of the E-beam treatment.

Energy transfer effect of hybrid organic rubrene nanorod with CdSe/ZnS quantum dots: Application to optical waveguiding modulators

Organic rubrene (5,6,11,12-tetraphenyltetracene) nanorods (NRs) were fabricated through the physical vapor transport method for the study of active fluorescence optical waveguiding and its modulation. The functionalized CdSe/ZnS quantum dots (QDs) with blue and green emissions were partially attached to the surface of the rubrene NR. Using a high resolution laser confocal microscope (LCM), the nanoscale photoluminescence (PL) intensity of the pristine rubrene portion of the hybrid NR/QDs was observed to be considerably enhanced after it was attached with blue (or green) QDs. The nanoscale optical waveguiding characteristics of the hybrid NR/QDs were investigated in terms of the output LCM PL spectra as a function of propagation distance. We observed more efficient optical waveguiding characteristics from the hybrid rubrene NR/blue-QDs than from the pristine NR and the hybrid rubrene NR/green-QDs. These results can be analyzed in terms of the higher Förster resonance energy transfer efficiency for hybrid rubrene NR/blue-QDs system. The results and analysis were supported by a drastic decrease of exciton lifetime of QDs in the hybrid region as measured by time-resolved PL decay curves.

Gold nanoparticle hybridized rubrene nanofibers made by electrospinning: enhancement of optical and structural properties

We prepared gold nanoparticle (Au NP) hybridized organic rubrene nanofibers (NFs) using a convenient electrospinning method. Au NPs of size 2–3 nm were incorporated throughout the light emitting rubrene NFs, which was confirmed by high resolution transmission electron microscopy. Au NP hybridized rubrene NFs showed a distinct nanoporous surface, compared to the smooth surface of rubrene NFs. Nanoscale confocal spectroscopy was performed on a single NF level and the results showed that the photoluminescence (PL) of the hybrid NFs made with 15 wt% Au NP mixture solution was 2.5 times higher than the PL of the rubrene NFs. And the optical extinction (scattering and absorption) of hybrid NFs increased monotonically with increasing Au NP concentrations. These enhanced optical properties of hybrid NFs were attributed to localized surface plasmon resonance of the embedded Au NPs. Structural modification from the monoclinic phase to the orthorhombic phase of the rubrene structure was obtained by XRD analysis indicating a better ordering along the rubrene ab plane of the hybrid NFs.

Anisotropic optical absorption of organic rubrene single nanoplates and thin films studied by μ-mapping absorption spectroscopy

Local absorption spectra and absorption coefficients were obtained from organic rubrene single nanoplates. Absorption along the b-axis was higher than along the a-axis for polarized illumination on an ab-faced single-crystal rubrene nanoplate, and the lowest crystal transition peak (∼530 nm) relatively increased in size with an increasing incidence angle due to the anisotropic absorption strength along the crystal axes. Rubrene thin films grown by organic molecular beam deposition displayed microscopically varying absorption spectra; the relative peak height of the M-polarized band and the overall absorption strength were strongest with polarized illumination along the c-axis.

Polarized photoluminescence characteristics of rubrene sheets with nanometer thickness

We report on the temperature dependence of the polarized photoluminescence (PL) exhibited by crystalline organic rubrene sheets with a thickness of \ensuremath{\sim}60 nm. To probe the correlations between the electronic states and the molecular stacking of rubrene molecules, the polarized PL spectrum of a single rubrene sheet was analyzed as a function of temperature from 10 to 250 K. Drastic changes were observed in PL peak positions and intensities \ensuremath{\sim}100 and \ensuremath{\sim}170 K, which were likely related to variations in molecular ordering with temperature. The changes in the PL characteristics of the sheet \ensuremath{\sim}170 K are similar to those observed for rubrene bulk crystals, in terms of the enhancement of mobility and crystallinity. In addition, \ensuremath{\sim}100 K, the reversal of the relative ratio of PL intensities corresponding to two crystalline axes, $a$ and $b$, in the rubrene sheets suggested an anisotropic variation in the molecular ordering along these two crystalline axes.

Luminescence, charge mobility, and optical waveguiding of two-dimensional organic rubrene nanosheets: Comparison with one-dimensional nanorods

Intrinsic characteristics of organic and inorganic nanostructures depend on their physical dimensions (i.e., size and shape) and crystallinity. Here, we compared the nanoscale optical and electrical properties of organic rubrene one-dimensional (1-D) nanorods (NRs) and two-dimensional (2-D) nanosheets (NSs). From high-resolution laser confocal microscope photoluminescence (PL) measurements, the light-emission characteristics of 2-D rubrene NSs varied with the crystalline domain direction, indicating intrinsic PL anisotropy, which was distinguishable from 1-D rubrene single NRs, because of anisotropy π–π stacking molecular arrangements. We also observed the variation of charge carrier mobility depending on the measured directions (i.e., anisotropy of charge transport) in rubrene NS-based field-effect transistors. The optical waveguiding properties of rubrene nanostructures were strongly correlated to the dimensionality of materials and PL anisotropy.

Electrospinning and optical characterization of organic rubrene nanofibers

We report on the preparation of continuous organic rubrene nanofibers using the electrospinning method. We added the minimal amount of poly (ethylene oxide) in the electro-spinning solution to provide the viscosity required for electrospinning. Optical characteristics such as absorption, photoluminescence, and Raman spectra all confirmed the successful formation of rubrene nanofibers. Confocal Raman spectra obtained from single rubrene nanofibers showed co-existence of the amorphous and the crystal phase of the rubrene molecule. We also demonstrated that our rubrene nanofibers can be used as efficient optical waveguides. Our result suggests that abundant fluorescent, continuous nanofibers of small molecule materials can be successfully prepared using electrospinning.

Tuning photoluminescence of organic rubrene nanoparticles through a hydrothermal process

Light-emitting 5,6,11,12-tetraphenylnaphthacene (rubrene) nanoparticles (NPs) prepared by a reprecipitation method were treated hydrothermally. The diameters of hydrothermally treated rubrene NPs were changed from 100 nm to 2 μm, depending on hydrothermal temperature. Photoluminescence (PL) characteristics of rubrene NPs varied with hydrothermal temperatures. Luminescence of pristine rubrene NPs was yellow-orange, and it changed to blue as the hydrothermal temperature increased to 180°C. The light-emitting color distribution of the NPs was confirmed using confocal laser spectrum microscope. As the hydrothermal temperature increased from 110°C to 160°C, the blue light emission at 464 to approximately 516 nm from filtered-down NPs was enhanced by H-type aggregation. Filtered-up rubrene NPs treated at 170°C and 180°C exhibited blue luminescence due to the decrease of intermolecular excimer densities with the rapid increase in size. Variations in PL of hydrothermally treated rubrene NPs resulted from different size distributions of the NPs.