Copper Phthalocyanine Films Research Articles

Structural properties of copper phthalocyanine films grown by electrophoretic deposition process

In this work, organic film of copper phthalocyanine (CuPc) was prepared by electrophoretic deposition process. The structural, morphological and optical properties of CuPc films were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and UV-VIS spectroscopy. The effect of annealing temperature on properties of CuPc films has been studied. When the annealing temperature is increased, the phase transformation of CuPc gradually changes from α-phase to β-phase. The optical absorption spectra of films at the different annealing temperature demonstrated the characteristics of B-band and Q-band of CuPc films. Moreover, the morphology of films exhibited the rod-like structure, while at higher annealing temperature the morphology of CuPc films change to sheet-like structure.

Femtosecond to nanosecond excited state dynamics of vapor deposited copper phthalocyanine thin films.

Vapor deposited thin films of copper phthalocyanine (CuPc) were investigated using transient absorption spectroscopy. Exciton-exciton annihilation dominated the kinetics at high exciton densities. When annihilation was minimized, the observed lifetime was measured to be 8.6 ± 0.6 ns, which is over an order of magnitude longer than previous reports. In comparison with metal free phthalocyanine (H2Pc), the data show evidence that the presence of copper induces an ultrafast relaxation process taking place on the ca. 500 fs timescale. By comparison to recent time-resolved photoemission studies, this is assigned as ultrafast intersystem crossing. As the intersystem crossing occurs ca. 10(4) times faster than lifetime decay, it is likely that triplets are the dominant excitons in vapor deposited CuPc films. The exciton lifetime of CuPc thin films is ca. 35 times longer than H2Pc thin films, while the diffusion lengths reported in the literature are typically quite similar for the two materials. These findings suggest that despite appearing to be similar materials at first glance, CuPc and H2Pc may transport energy in dramatically different ways. This has important implications on the design and mechanistic understanding of devices where phthalocyanines are used as an excitonic material.

Effect of dispersion of gold nanoparticles on the properties and alignment of liquid crystalline copper phthalocyanine films

The inclusion of hexadecylamine capped gold nanoparticles (AuNPs) into the ordered matrix of hexagonal columnar mesophase of copper phthalocyanine (CuPc) has been investigated. The effects of AuNPs on the liquid crystalline behaviour, optical and electrical properties of CuPc films is investigated by different physical methods. The molecules orientation in the films of CuPc and its composites with AuNPs, deposited on the surface of one substrate and between two electrodes, is studied by polarized Raman spectroscopy and polarized microscopy. It has been shown that thin films of the composites confined between ITO and Al electrodes are characterized by homeotropic alignment while no homeotropic alignment was observed in films deposited on ITO substrate with air constituting the upper interface. The I(V) dependences for the films confined between ITO and Al electrodes were measured. Appreciable enhancement of the DC conductivity is observed in the case of composites containing gold nanoparticles.

Ambience-related adsorbates on CuPc surface—Photoemission and thermal desorption spectroscopy studies for control of organic electronics degradation processes

In present work, using the angle-resolved X-ray photoelectron spectroscopy, the chemical structure of the 32nm-thick copper phthalocyanine (CuPc) films surface was revealed upon long-term ambient air exposure. The existence of ambience-related components was detected in the C1s, N1s and O1s spectra and their depth distributions within the CuPc layer were analyzed. Combined ultraviolet photoelectron and photoemission yield spectroscopies provided information concerning redistribution of electron density in surface region which was reflected in surface band bending increase by 0.91eV, shift in electron affinity of 0.26eV and work function variation of 1.17eV. The kind and amount of desorbed molecules or atoms from phthalocyanine’s surface were investigated by the thermal desorption spectroscopy. Quantified activation energies for desorption of C, N2, O2 and H2O species with values in the range of 120–166kJ/mol indicated chemical adsorption process (of rather covalent than ionic nature) of the ambience related adsorbates on organic surface.

Effects of Heat Annealing on the Gas Sensing Properties of Spin Coated Unsubstituted Copper Phthalocyanine Films

Unsubstituted copper phthalocyanine (CuPc) thin films on glass substrate were prepared using spin coating technique. The effects of heat annealing of CuPc films on the NO2 gas sensing properties were studied. The results showed that the films annealed at 150°C have highest sensitivity, highest response rate and lower response time. Sensitivity and response rate were decreased and response time was increased after annealing with temperature 200°C and above. The duration over which the films were annealed changes the gas sensing properties. Highest sensitivity, highest response rate, lower response time and highest recovery rate were observed for 2 hour (150°C) annealed films. Longer annealing time causes the decrease of sensitivity, response rate and recovery rate and increase of response time however improves recovery ratio. The heat treatment limited to the temperature of 150°C for 2 hours duration improves the sensing properties of the films. Hence heat annealed unsubstituted CuPc spin coated films can be used as nitrogen dioxide gas sensor.

Microspot two-photon photoemission spectroscopy for CuPc film on HOPG

Microspot two-photon photoemission (micro-2PPE) spectroscopy has been applied to measure the lateral distribution of unoccupied levels on copper phthalocyanine (CuPc) film on HOPG. In addition to the LUMO-derived level and the image potential state (IPS) on the film, we identified the modified IPS which is stabilized by the hole localized in a molecule. We show that modified IPS is observed only on bilayer area, reflecting the localization of the hole in a molecule. The modified IPS is absent on monolayer area, because the hole strongly interacts with substrate.

Copper phthalocyanine thin films on Cu(111): Sub-monolayer to multi-layer

Abstract Scanning tunneling microscopy (STM) has been used to observe the growth mode and crystal structure of sub-monolayer (ML) to multilayer thin films of copper phthalocyanine (CuPc) molecules on the Cu(111) surface at room temperature (RT). At sub-ML coverage the molecules are mobile on the surface. At approximately one ML coverage the molecules become sterically confined and lying flat on the Cu substrate form an ordered, multi-domained, 2D oblique lattice. As coverage is increased beyond 1 ML the molecule–substrate interaction diminishes in strength while the intermolecular interaction begins to dominate, causing the layer separation to increase, and the crystal domain size and lattice constants to shrink as the crystal structure begins to more closely resemble the bulk α-phase CuPc molecular solid. This trend continues for the layer-by-layer growth of 3 complete ML, eventually giving way to the emergence of large 3D islands at a coverage equivalent to 4 ML.

Site-specific probing of charge transfer dynamics in organic photovoltaics

We report the site-specific probing of charge-transfer dynamics in a prototype system for organic photovoltaics (OPVs) by picosecond time-resolved X-ray photoelectron spectroscopy. A layered system consisting of approximately two monolayers of C60 deposited on top of a thin film of Copper-Phthalocyanine (CuPC) is excited by an optical pump pulse and the induced electronic dynamics are probed with 590 eV X-ray pulses. Charge transfer from the electron donor (CuPC) to the acceptor (C60) and subsequent charge carrier dynamics are monitored by recording the time-dependent C 1s core level photoemission spectrum of the system. The arrival of electrons in the C60 layer is readily observed as a completely reversible, transient shift of the C60 associated C 1s core level, while the C 1s level of the CuPC remains unchanged. The capability to probe charge transfer and recombination dynamics in OPV assemblies directly in the time domain and from the perspective of well-defined domains is expected to open additional pathways to better understand and optimize the performance of this emerging technology.

Toward Single-Crystal Hybrid-Carbon Electronics: Impact of Graphene Substrate Defect Density on Copper Phthalocyanine Film Growth

Graphene has long been recognized as a potential replacement for indium tin oxide as a transparent conducting substrate that may not only be cheaper to manufacture but also may provide mechanical flexibility and templating for preferential organic film growth. Here, we report the discovery that the thin film growth mode and crystal structure of copper phthalocyanine (CuPc), a prototype organic semiconductor, is extremely sensitive to even atomic-scale defects (e.g., steps) on the graphene surface and that high quality films can be grown with a well-defined crystal orientation that should be favorable for optimized solar cell applications. The initial growth involves flat-lying copper phthalocyanine molecules in a triclinic brickstone crystal with (012̅) orientation. Thicker films on pristine graphite, as well as thin films on lower quality graphene, show an orientational transition to the flat-lying (112̅)-oriented brickstone, which nucleates near film defects and grows in more compact 3D islands. The thickness dependent transition between these two flat-lying crystal orientations is sensitive to substrate defect density since this determines the extent to which initial island elongation along the substrate can alleviate strain in the film. The sensitivity of copper phthalocyanine film morphology demonstrates the extreme importance of graphene substrate quality to controlling organic film growth. The high crystallinity and optimal molecular orientation achieved here implies a new driving force for high performance organic optoelectronics based on substrate-controlled crystal engineering.

Molecular arrangement investigation of copper phthalocyanine grown on hydrogen passivated Si(111) surfaces

Abstract Chemical, electronic and structural properties of ultra thin films of copper phthalocyanine (CuPc) grown on hydrogen passivated silicon (1 1 1) surfaces were investigated in situ by X-ray photoelectron spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), X-ray photoelectron diffraction (XPD) and electron diffraction (LEED). The early stages of copper phthalocyanine adsorption (1–2) were characterized by the saturation of surface defects and by a flat lying disposition on the surface. Upon further CuPc coverage, the passivation of Si surfaces resulted in the molecule taking a standing position in films. The molecular packing deduced from these studies appears very close to the one in the bulk α phase of CuPc. The work function of the films was found to be decreasing during the growth and was correlated with the molecular orientation.

Nonlinear features of surface-enhanced Raman scattering revealed under non-resonant and resonant optical excitation

By performing comparative Raman studies on nanometric thin films (9.5, 39, 88 and 185 nm) of copper phthalocyanine (CuPc) deposited on glass, Au and Ag supports, we demonstrate that the mechanism of the surface-enhanced Raman scattering (SERS) generated on Au and Ag substrates differs in the Stokes and anti-Stokes Raman branches depending on whether non-resonant (515.5 nm) or resonant (647.1 nm) optical excitation is applied. The evaluation of the SERS effect via the IaS/IS ratio reveals that this ratio is smaller or larger than that predicted by the Boltzmann law for non-resonant or resonant optical excitation, respectively. In the former case, the enhancement of the Stokes Raman emission is similar to a stimulated Raman process resulting from the plasmon coupling associated with the incident excitation light and spontaneous Stokes Raman emission. For the latter case, the amplification of the anti-Stokes Raman emission results from a wave-mixing process reminiscent of a single-beam CARS effect.

Photovoltaic properties of a heterojunction based on copper phthalocyanine films on the surface of polycrystalline cadmium sulfide

The photovoltaic effect has been detected and studied in thin-film structures based on thermally deposited 200-nm-thick copper phthalocyanine (CuPc) films on the surface of polycrystalline CdS. The structures under study demonstrate the linear current-voltage characteristics at external electric fields to 3.5 × 104 V/cm. Two components of the photovoltage of different signs have been revealed when the sample is illuminated in the wavelength range from 350 to 700 nm. The first component has the positive sign on the CuPc film side and is observed when using the radiation with a wavelength lesser than 500 nm, i.e., in conditions of predominant absorption of the radiation in the CdS layer. The second component has the negative sign on the CuPc film side and is observed when using the radiation with a wavelength in the range from 500 to 570 nm, corresponding to the spectral region of the absorption edge of the CuPc films. The dependences of the photovoltage on the radiation intensity studied in the range from 5 × 1012 to 1014 photons cm−2 s−1 are different in the cases of the two detected components. Mechanisms of generation of the photovoltage components associated with a change in the band bending during photogeneration of charge carriers in the region of space charge in CdS and a change in conditions of the charge transfer in the interfacial CuPc/CdS region during the radiation absorption in the CuPc film have been proposed.

Electronic properties of the interface between hexadecafluoro copper phthalocyanine and unsubstituted copper phthalocyanine films

The formation of an interface during the deposition of unsubstituted copper phthalocyanine (CuPc) films on the surface of hexadecafluoro copper phthalocyanine (F16-CuPc) films is studied. An incident low-energy electron beam with energies from 0 to 25 eV is used to test the surface under study according to the very-low-energy electron-diffraction technique (VLEED) in the mode of total current spectroscopy. For F16-CuPc films, the structure of the maxima in the total current spectra and its main differences from the structure of the maxima for the CuPc film are determined in the energy range from 5 to 15 eV above the Fermi level. The differences in the structure of vacant electron orbitals for CuPc and F16-CuPc are also revealed using density functional theory calculations. As a result of an analysis of variations in the intensities of the total current spectra of the CuPc and F16-CuPc films, it is assumed that an intermediate layer up to 1 nm thick appears during the formation of an interface between these films, which is characterized by a spread of the features in the total current spectrum. The height, width, and change in the work function are determined for the studied F16-CuPc/NuPc interface barrier. A decrease in the level of vacuum by 0.7 eV occurs in the boundary region, which corresponds to electron density transfer from the CuPc film toward the F16-CuPc substrate.

Fabricating organic transistors based on domain‐ordered copper phthalocyanine film grown on oligothiophene epitaxial substrate

AbstractOrganic field‐effect transistors were fabricated using a domain‐ordered copper phthalocyanine (CuPc) thin film as the active layer prepared by weak epitaxial growth (WEG) technology. CuPc was deposited onto α‐sexithiophene (α‐6T) and α,ω‐dihexylsexithiophene (α,ω‐DH6T) films acting as the epitaxial substrate to realize the domain‐order growth. As a result, the thin‐film morphology of CuPc exhibits many re‐ gional domain‐ordered structures measured by atomic force microscopy and X‐ray diffraction. The field‐effect mobilities are 0.11 and 0.085 cm2/Vs for the devices with CuPc/α‐6T and CuPc/α,ω‐DH6T, respectively. The threshold voltages were –7 V and –13 V for CuPc/α‐6T and CuPc/α,ω‐DH6T, respectively. The improved device performance could be attributed to the domain‐order structure of the CuPc thin film. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Static electric field enhanced recrystallization of copper phthalocyanine thin film during annealing

External electric field may be applied on an organic semiconductor layer at different stages of its fabrication to tailor the film structure and morphology as per the need of the device being fabricated. In this paper, we present an easy to implement method of applying static electric field on the thin film of copper phthalocyanine (CuPc) during its post deposition annealing, and discuss its effects on the film properties. Characterization by x-ray diffraction (XRD) spectroscopy and field emission scanning electron microscopy (FESEM) reveals that the applied electric field significantly enhances the recrystallization process of CuPc thin film. Thus larger grains and longer nanorods are formed in the film improving its crystallinity due to electric field. The effects of the ambient pressure and electric field strength have also been reported. The possible reasons for the observed phenomena have been discussed.

A novel glucose biosensor based on the immobilization of glucose oxidase on layer-by-layer assembly film of copper phthalocyanine functionalized graphene

A negatively charged glassy carbon electrode (GCE) was formed through the electrochemical modification of sulfanilic acid (ABS). Subsequently, graphene composites functionalized with copper phthalocyanine-3,4′,4″,4‴-tetrasulfonic acid tetrasodium salt (TSCuPc) or alcian blue pyridine variant (AB) were assembled layer-by-layer (LbL) via alternate electrostatic adsorption onto the ABS/GCE surface to obtain a uniform and stable graphene multilayer film modified electrode. With glucose oxidase (GOD) as an enzyme model, a novel GOD/Nafion/(LbL)3.5/ABS/GCE electrochemical biosensor has been developed. SEM and Raman spectra were utilized to characterize the functionalized graphene nanocomposites and modified electrodes. The electrochemical performance of the biosensor was investigated by cyclic voltammetry. The results demonstrated that the graphene multilayer film significantly enhanced the electrocatalytic activity of the modified electrode toward O2 reduction. Based on the O2 consumption during the oxidation process of glucose, the as-prepared biosensor exhibited a low detection limit of 0.05mmolL−1, excellent reproducibility, stability, sensitivity and selectivity, and its response was linear up to 8mmolL−1 glucose concentration. Accordingly, the multilayer film consisting of copper phthalocyanine functionalized graphene nanocomposites offers a novel and effective platform for the electrochemical biosensing applications.

Passivation of surface states in the ZnO nanowire with thermally evaporated copper phthalocyanine for hybrid photodetectors

The adsorption of O2/H2O molecules on the ZnO nanowire (NW) surface results in the long lifetime of photo-generated carriers and thus benefits ZnO NW-based ultraviolet photodetectors by suppressing the dark current and improving the photocurrent gain, but the slow adsorption process also leads to slow detector response time. Here we show that a thermally evaporated copper phthalocyanine film is effective in passivating surface trap states of ZnO NWs. As a result, the organic/inorganic hybrid photodetector devices exhibit simultaneously improved photosensitivity and response time. This work suggests that it could be an effective way in interfacial passivation using organic/inorganic hybrid structures.

Sensitivity boosting in solid-state NMR of thin organic semiconductors by a paramagnetic dopant of copper phthalocyanine

Sensitivity enhancements in cross-polarization magic-angle-spinning (CPMAS) solid-state NMR spectra of organic thin-film semiconductors are reported. A vacuum-deposited paramagnetic dopant on the semiconductor films reduces 1H T1 relaxation time, enabling faster repetition of NMR measurements. When the thickness of the films is between 50 and 100nm, 1H spins are well polarized by 1H–1H spin diffusion, giving the maximum sensitivity without harmful effects such as paramagnetic shift, broadening, and quenching of CPMAS signals. The binary films of copper phthalocyanine (CuPc) and phenyldipyrenylphosphine oxide (POPy2) show a threefold reduction of the NMR measurement time.

Enhanced photovoltaic performance of copper phthalocyanine by incorporation of polyoxometalate

The improvement of the photoconversion efficiency has become a crucial issue for the utilization of organic semiconductors. Here we prepared a composite film of copper phthalocyanine (CuPc) and polyoxometalates (POMs) which displayed the enhanced photovoltaic performance. Especially, the photocurrent response and power conversion efficiency of CuPc/POMs composite film showed a 6-fold and a 10-fold increase, respectively, as compared to the single CuPc film. Based on the measurements of surface photovoltage technique, the enhanced photocurrent should be attributed to the occurrence of the photoinduced electron transfer between CuPc and POMs, which increases the dissociation of excited electron–hole pairs (excitons). Moreover, the CuPc/POMs composite film exhibited good photoelectrocatalytic performance for the oxidation of hydrazine. These results demonstrate that the incorporating of appropriate POMs into organic semiconductors is a promising route for developing and optimizing organic photovoltaic and photoelectrochemical devices.

Influences of Ion-Induced Defects on Growth of Copper-Phthalocyanine Film on Graphene Substrates

Influences of argon ion-induced defects on growth of copper-phthalocyanine (CuPc) films on graphene were studied with atomic force microscope, X-ray diffraction, and high-resolution electron energy-loss spectroscopy (HREELS). Points defects and edges on graphene were found to be favorable sites for initial nucleation of CuPc. On as-grown graphene substrate with low defect density, CuPc nucleation begins at edges of the graphene sheets and then further grows into large islands with regular edges and smooth surfaces. On graphene subjected to argon ion treatment, which is known to induce surface defects, CuPc begins to nucleate at the defect positions, giving rise to crystals of much smaller sizes than those grown on a pristine graphene substrate. Such ion-induced modifications are correlated to changes in HREELS spectra of the corresponding CuPc films.