Copper Hexadecafluorophthalocyanine Research Articles

Photoswitches and Phototransistors from Organic Single‐Crystalline Sub‐micro/nanometer Ribbons

Photoelectronic devices of organic semiconductors are of great interest recently because organic semiconductors have many fundamental advantages over their inorganic counterparts. For example, their low cost is ideal for large-area applications and their mechanical flexibility makes them naturally compatible with plastic substrates for lightweight and foldable products. The most attractive prospect, however, is their incorporation of functionality by molecular design. Phototransistors have much higher sensitivity and lower noise than photodiodes and use these advantages to combine light detection and signal magnification properties that realize greater functionality in a single device. This is an important aspect of optoelectronic integration. Since the first concept of a phototransistor was proposed by William Shockley in 1951, inorganic phototransistors have been quickly developed and used in a variety of applications. However, few reports in the literature have addressed phototransistors made of organic semiconductors, especially organic single crystals. Organic single crystals have important merits in the study of intrinsic properties and for the fabrication of high-quality devices and circuits. Here, we used an organic semiconductor, copper hexadecafluorophthalocyanine (F16CuPc), as the candidate to introduce single-crystalline photoswitches and phototransistors of organic semiconductors. F16CuPc was selected not only because of its remarkable air-stable, n-type properties but also because of its high thermal and chemical stability. Bao et al. first paid attention to this compound in 1998. Recently, Dosch and Barrena and co-workers carefully investigated its structure and self-organization properties on a solid surface. In addition, we synthesized single-crystalline sub-micro/nanoribbons of the compound by a physical vapor transport technique and studied its field-effect performance; we demonstrated its high field-effect mobility and on/ off ratio in transistors based on an individual ribbon. However, the optical properties of this air-stable, n-type material, are still unclear. In this Communication, we study these properties by using devices made of single-crystalline sub-micro/ nanometer ribbons of F16CuPc. Single-crystalline sub-micro/nanometer ribbons of F16CuPc were synthesized and transferred or in-situ patterned onto Si/ SiO2 (300 nm) substrates, as previously described. [6,7] Devices based on an individual sub-micro/nanometer ribbon were fabricated by the “multiple-times gold-wire mask moving” technique based on the asymmetrical drain/source electrode (Au/Ag) configuration shown in Figure 1—because such a configuration was beneficial for injection, transport, and collection. The ribbon thickness in the devices was measured carefully by atomic force microscopy. C O M M U N IC A TI O N

Charge transfer effects in organic field-effect transistors containing a donor/acceptor heterojunction

Heterojunction organic field-effect transistors (OTFTs) based on copper phthalocyanine (CuPc) as p-type and on copper hexadecafluorophthalocyanine (F 16CuPc) or 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as n-types were fabricated and studied. They were shown to operate in unipolar mode where hole current was recorded with values approaching those of CuPc-based single-layer device. However, due to a charge transfer phenomenon between CuPc and F 16CuPc, the occurrence of a build-in electrical field at the CuPc/F 16CuPc interface is shown to influence the transport properties at low drain-source voltages and to induce a non-ideal ohmic behavior in OTFT characteristics. This effect is not observed in the case of CuPc/TCNQ because of a larger energy difference between HOMO and LUMO energy levels of CuPc and TCNQ, respectively.

Charge Carrier Transporting, Photoluminescent, and Electroluminescent Properties of Zinc(II)-2-(2-hydroxyphenyl)benzothiazolate Complex

Zinc(II)-2-(2-hydroxyphenyl)benzothiazolate complex is an excellent white-light-emitting material. Despite some studies devoted to this complex, no information on the real origin of the unusually broad electroluminescent (EL) emission is available. Therefore, we investigate photoluminescent and EL properties of the zinc complex. Orange phosphorescent emission at 580 nm was observed for the complex in thin film at 77 K, whereas only fluorescent emission was obtained at room temperature. Molecular orbitals, excitation energy, and emission energy of the complex were investigated using quantum chemical calculations. We fabricated the device with a structure of ITO/F16CuPc(5.5 nm)/Zn-complex/Al, where F16CuPc is hexadecafluoro copper phthalocyanine. The EL spectra varied strongly with the thickness of the emissive layer. We observed a significant change in the emission spectra with the viewing angles. Optical interference effects and light emission originating both from fluorescence and from phosphorescence ca...

Copper hexadecafluorophthalocyanine and copper phthalocyanine as a pure organic connecting unit in blue tandem organic light-emitting devices

A nondoped organic system of copper hexadecafluorophthalocyanine (F16CuPc)∕copper phthalocyanine (CuPc) has been investigated as a connecting unit for deep-blue electrofluorescent tandem organic light-emitting devices (OLEDs) based on 2-methyl-9,10-di(2-naphthyl) anthracene emission. Such devices exhibited a doubling in current efficiency from 0.63to1.47cd∕A at J=100mA∕cm2 as compared to the single-unit device. The pure organic connecting unit showed superior optical transparency (∼100%), resulting in minimal microcavity effect in the devices. Interface dipole and band bending on both sides of the F16CuPc∕CuPc interface suggested the formation of an intrinsic p-n junction, which is a prerequisite of an effective connecting unit leading to a dramatic performance improvement in the tandem OLEDs.

Field emission from copper phthalocyanine and copper hexadecafluorophthalocyanine nanowires

Copper phthalocyanine (CuPc) and copper hexadecafluorophthalocyanine (F 16CuPc) nanowires were fabricated by vapor deposition. The nanowires were studied by scanning electron microscopy and transmission electron microscopy. Field emission properties of these nanowires were studied. The field emission properties were strongly dependent on the substrate temperature and the material used, and the best results are obtained for β-phase CuPc nanoribbons. Different dependences of field emission properties on the substrate temperature were obtained for the two materials investigated. The obtained results are discussed.

Organic field-effect inversion-mode transistors and single-component complementary inverters on charged electrets

We demonstrate that the electrostatic polarization of an organic semiconductor (OSC) by a gate dielectric with stored charges and electric fields enables the realization of both threshold voltage tuning and inversion process control of OSC thin-film field-effect transistors (OFETs). As a result, OFETs based on typically unipolar n-channel copper hexadecafluorophthalocyanine semiconductor thin films, deposited on a silicon dioxide quasipermanent charged electret as a gate insulator, show unipolar p-channel “inversion” operation in ambient air and form complementary monolithic, single-semiconductor inverter circuits. The field produced by patterned, grid-controlled negative corona charging and subsequent thermal annealing (before semiconductor deposition) electrostatically induces sufficient positive charges to provide significant hole mobility, ca. 0.011cm2V−1s−1, in response to moderate additional negative gate voltages.

High-Performance Air-Stable n-Type Transistors with an Asymmetrical Device Configuration Based on Organic Single-Crystalline Submicrometer/Nanometer Ribbons

High-performance air-stable n-type field-effect transistors based on single-crystalline submicro- and nanometer ribbons of copper hexadecafluorophthalocyanine (F(16)CuPc) were studied by using a novel device configuration. These submicro- and nanometer ribbons were synthesized by a physical vapor transport technique and characterized by the powder X-ray diffraction pattern and selected area electron diffraction pattern of transmission electron microscopy. They were found to crystallize in a structure different from that of copper phthalocyanine. These single-crystalline submicro- and nanometer ribbons could be in situ grown along the surface of Si/SiO(2) substrates during synthesis. The intimate contact between the crystal and the insulator surface generated by the "in situ growing process" was free from the general disadvantages of the handpicking process for the fabrication of organic single-crystal devices. High performance was observed in devices with an asymmetrical drain/source (Au/Ag) electrode configuration because in such devices a stepwise energy level between the electrodes and the lowest unoccupied molecular orbital of F(16)CuPc was built, which was beneficial to electron injection and transport. The field-effect mobility of such devices was calculated to be approximately 0.2 cm(2) V(-)(1) s(-)(1) with the on/off ratio at approximately 6 x 10(4). The performances of the transistors were air stable and highly reproducible.

Frontier Electronic Structures in Fluorinated Copper Phthalocyanine Thin Films Studied Using Ultraviolet and Inverse Photoemission Spectroscopies

Ultraviolet photoemission and inverse photoemission spectroscopy was used to compare the electronic structure of copper phthalocyanine, copper octafluorophthalocyanine, and copper hexadecafluorophthalocyanine thin films. A rigid shift to lower energy was observed for both the occupied and unoccupied electronic states as the number of fluorine atoms around the phthalocyanine ring increased. The spectral features of the fluorine-substituted derivatives were otherwise very similar to copper phthalocyanine, and no change in the transport gap energy was observed. Vacuum level shifts were observed at the interface with polycrystalline gold substrates of sufficient magnitude to consistently pin the substrate Fermi level near the middle of the HOMO-LUMO gap. The calculated barrier heights for electron and hole injection across the interface were therefore equal, and no correlation with fluorine substitution was found.

Molecular Interface Effect of Heterogeneous Molecular Junctions Consisting of Nonfluorinated and Fluorinated Phthalocyanines

We report the tunneling behavior of homogeneous and heterogeneous molecular junctions using p-type molecules of iron phthalocyanine (FePc), phthalocyanine (H(2)Pc), and copper(II) octaalkoxyl substituted phthalocyanine (CuPcOC8) and n-type molecule of copper hexadecafluorophthalocyanine (F(16)CuPc). The molecular films formed on the electrode surfaces were inspected by X-ray photoelectron spectroscopy (XPS). The measured characteristic tunneling curves of single-component phthalocyanines revealed comparable energy gaps for homogeneous tunneling junctions using the photoemission method. In contrast, for the heterogeneous tunnel junctions of mixed phthalocyanines including fluorinated phthalocyanine a distinctive offset of the energy gaps to the positive bias voltage direction can be clearly identified. It is suggested that the substitution of phthalocyanines and surface affinity of phthalocyanines could contribute to the controlled phase separation within the heterogeneous tunneling junctions. The apparent shift of the tunneling spectra is attributed to the existence of an internal electric field originated with the phase separation of the binary mixture of p-type and n-type phthalocyanines within the tunneling junction.

Organic Light-Emitting Diodes with F16CuPC as an Efficient Hole-Injection Layer

We report a new hole-injection material, copper hexadecafluorophthalocyanine (F16CuPC) for organic light-emitting diodes (OLEDs) consisting of N,N’-di(1-naphthyl)-N,N’-diphenylbenzidine ( -NPD) as a hole-transport layer and 8-tris-hydroxyquinoline aluminum (Alq3) as a light-emitting and electron-transport layer. The insertion of the F16CuPC between indium-tin oxide (ITO) and -NPD reduces the operating voltage significantly and thereby increases the luminous eciency. By measuring the device characteristics for various F 16CuPC thicknesses, we find that an optimum F16CuPC thickness is about 15 nm. At a luminance of 1000 cd/m 2 , the

Metal Phthalocyanine Nanoribbons and Nanowires

Nanoribbons and nanowires of different metal phthalocyanines (copper, nickel, iron, cobalt, and zinc), as well as copper hexadecafluorophthalocyanine (F(16)CuPc), have been grown by organic vapor-phase deposition. Their properties, as a function of substrate type, source-to-substrate distance, and substrate temperature, were studied by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and absorption measurements. The size and morphology of the nanostructures were found to be mainly determined by the substrate temperature. The crystal structure was dependent on the substrate temperature as well. At substrate temperatures below 200 degrees C, in addition to straight nanoribbons, twisted nanoribbons were found for all investigated materials except F(16)CuPc, which formed helical nanoribbons upon exposure to an electron beam. The formation of different nanostructures (nanoribbons, twisted nanoribbons, and helical nanoribbons) is discussed.

Interfacial electronic structure of copper phthalocyanine and copper hexadecafluorophthalocyanine studied by photoemission

Electronic structures of the heterojunction between copper phthalocyanine (CuPc) and copper hexadecafluorophthalocyanine (F16CuPc) were studied with ultraviolet photoemission spectroscopy. Band bending and an interface dipole were observed at the interface due to the formation of an electron accumulation layer and a depletion layer in F16CuPc and CuPc, respectively. Such an energy level alignment leads to interesting ambipolar characteristics for application of the CuPc∕F16CuPc junction in organic field-effect transistors.

Integrated shadow mask method for patterning small molecule organic semiconductors

We have developed a simple and efficient method for patterning small molecule semiconductors for applications in the field of organic electronics. In our approach, a profile is created using a single layer of photoresist, defining the regions where the organic semiconductor is to be deposited. Subsequent deposition of a small molecule semiconductor results in a discontinuity of the semiconductor film at the photoresist edge. The resulting transistor characteristics have an off current that is systematically below 1pA. We demonstrate both p-type and n-type organic thin-film transistors using this method, using pentacene and copper hexadecafluorophthalocyanine (F16CuPc), respectively.

P-186: Enhanced Efficiency and Stability of Organic Light-Emitting Diodes with Copper Hexadecafluorophthalocyanine Doped Hole Transport Layer

We report the enhancement of the electroluminescence (EL) efficiency and the device stability of organic light-emitting diodes (OLEDs) by inserting a copper hexadecafluorophthalocyanine (F16CuPC)-doped N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (α-NPD) layer between an indium-tin oxide and α-NPD. Compared with the reference device consisting of the bilayer structure of α-NPD and tris(8-hydroxyquinoline) aluminum (Alq3), the devices having F16CuPC-doped α-NPD show not only an increased EL efficiency (∼4.5 cd/A compared with ∼3.8 cd/A for the reference device) and lower driving voltage but also a longer lifetime and smaller operating voltage variation over time. It is suggested that the improved device performance can be attributed to the higher hole-injection efficiency and thermal stability of the F16CuPC-doped α-NPD layer.

N-type organic field-effect transistor using polymeric blend gate insulator with controlled surface properties

Fabrication of n-type organic thin-film transistors (OTFTs) based on organic semiconductor and organic gate insulator is essential for the achievement of organic complementary logic circuit. This article deals with n-type OTFTs with copper hexadecafluorophthalocyanine (F16CuPc) and polymeric blend as an active semiconductor and a gate insulator, respectively. The gate insulator was prepared by blending poly(amic acid) and soluble polyimide with long alkyl side chains (C18 group), which make the surface of the gate insulator more hydrophobic. In order to reduce properties mismatch at interface between F16CuPc and the gate insulator, surface tension of the gate insulator was controlled to 39.1 dyn/cm, which is similar to that of F16CuPc (36.9 dyn/cm). AFM and X-ray diffraction measurements indicated that F16CuPc deposited on the gate insulator showed worm-like flat lying crystal and was highly ordered with a peak of 6.12°. The F16CuPc OTFTs with the gate insulator function as n-channel accumulation mode and their performance was better than that of F16CuPc OTFTs with SiO2, demonstrating its potential applications for flexible organic display. Charge carrier field-effect mobility, ION/IOFF, and subthreshold slope of the OTFT were 6 × 10−3 cm2/V s, 5.4 × 103, and 7.3 V/dec, respectively.

Synthesis and investigations of copper hexadecafluorophthalocyanine CuPcF16

In this work, the results of synthesis and characterization of hexadecafluorinated copper phthalocyanine CuPcF 16 are reported. The results of mass spectrometric studies of the composition of gaseous phase under solid compound and thermal properties of CuPcF 16 are presented. The vapour pressure of this phthalocyanine is determined as a function of temperature by the Knudsen effusion method, in which the rate of effusion of the equilibrium vapour through a small orifice was measured. It was shown that hexadecafluorosubstituted copper phthalocyanine exhibits lower volatility than its unsubstituted analogue. Besides, the spectral characterization of CuPcF 16 powder and films is carried out.

Synthesis and investigations of copper hexadecafluorophthalocyanine CuPcF 16

In this work, the results of synthesis and characterization of hexadecafluorinated copper phthalocyanine CuPcF 16 are reported. The results of mass spectrometric studies of the composition of gaseous phase under solid compound and thermal properties of CuPcF 16 are presented. The vapour pressure of this phthalocyanine is determined as a function of temperature by the Knudsen effusion method, in which the rate of effusion of the equilibrium vapour through a small orifice was measured. It was shown that hexadecafluorosubstituted copper phthalocyanine exhibits lower volatility than its unsubstituted analogue. Besides, the spectral characterization of CuPcF 16 powder and films is carried out.

Study of excited states of fluorinated copper phthalocyanine by inner shell excitation

Near edge X-ray absorption fine structure (NEXAFS) spectra of hexadecafluoro copper phthalocyanine (FCuPc) films (thickness of 50 Å) on MoS 2 substrates were observed near the carbon (C) and fluorine (F) K-edges. From the analysis of the dependence of C and F K-edge NEXAFS spectra on the photon incidence angle ( α), the average molecular tilt angle was determined to be 30°. The lowest and second lowest peaks in the F K-edge NEXAFS were assigned to the transition to σ ∗. In the ion time-of-flight mass spectra of FCuPc excited by photons near the F K-edge, F +, CF +, and CF 3 + ions were mainly observed. These results indicate that CC bonds as well as CF bonds are broken by the photon irradiation. From the analysis of the partial ion yield spectra of F + and CF + near the F K-edge, the lowest and second lowest peaks in the F K-edge NEXAFS spectra could be assigned to transitions to σ(CF) ∗ and σ(CC) ∗, respectively.

Contact resistance in organic transistors that use source and drain electrodes formed by soft contact lamination

Soft contact lamination of source/drain electrodes supported by gold-coated high-resolution rubber stamps against organic semiconductor films can yield high-performance organic transistors. This article presents a detailed study of the electrical properties of these devices, with an emphasis on the nature of the laminated contacts with the p- and n-type semiconductors pentacene and copper hexadecafluorophthalocyanine, respectively. The analysis uses models developed for characterizing amorphous silicon transistors. The results demonstrate that the parasitic resistances related to the laminated contacts and their coupling to the transistor channel are considerably lower than those associated with conventional contacts formed by evaporation of gold electrodes directly on top of the organic semiconductors. These and other attractive features of transistors built by soft contact lamination suggest that they may be important for basic and applied studies in plastic electronics and nanoelectronic systems based on unconventional materials.

Controlled Molecular Alignment in Phthalocyanine Thin Films on Stepped Sapphire Surfaces

We report a detailed study of the growth and structure of thin films of copper hexadecafluorophthalocyanine (F16CuPc) on sapphire. These films show very good out-of-plane order and have X-ray rocking widths of around 0.02°. If prepared under suitable conditions on A-plane sapphire substrates, the molecules align without significant azimuthal dispersion. Growth on MgO (001) and oxidized silicon wafers resulted in a comparable out-of-plane structure, but showed no azimuthal order. We find that the azimuthal alignment on sapphire is induced by the step edges along the c-axis of the sapphire, which serve as templates for the growth. For growth at different substrate temperatures, we find a monotonic change of the molecular out-of-plane tilt angle, as obtained from Raman scattering, which is accompanied by a change of the out-of-plane lattice parameter.