Phthalocyanine Thin Films Research Articles

Large Faraday Rotation in Optical-Quality Phthalocyanine and Porphyrin Thin Films.

The magneto-optical phenomenon known as Faraday rotation involves the rotation of plane-polarized light as it passes through an optical medium in the presence of an external magnetic field oriented parallel to the direction of light propagation. Faraday rotators find applications in optical isolators and magnetic-field imaging technologies. In recent years, organic thin films comprised of polymeric and small-molecule chromophores have demonstrated Verdet constants, which measure the magnitude of rotation at a given magnetic field strength and material thickness, that exceed those found in conventional inorganic crystals. We report herein the thin-film magnetic circular birefringence (MCB) spectra and maximum Verdet constants of several commercially available and newly synthesized phthalocyanine and porphyrin derivatives. Five of these species achieved maximum Verdet constant magnitudes greater than 105 deg T-1 m-1 at wavelengths between 530 and 800 nm. Notably, a newly reported zinc(II) phthalocyanine derivative (ZnPc-OT) reached a Verdet constant of -33 × 104 deg T-1 m-1 at 800 nm, which is among the largest reported for an organic material, especially for an optical-quality thin film. The MCB spectra are consistent with resonance-enhanced Faraday rotation in the region of the Q-band electronic transition common to porphyrin and phthalocyanine derivatives, and the Faraday A-term describes the electronic origin of the magneto-optical activity. Overall, we demonstrate that phthalocyanines and porphyrins are a class of rationally designed magneto-optical materials suitable for applications demanding large Verdet constants and high optical quality.

Directly Probing Interfacial Coupling in a Monolayer MoSe2 and CuPc Heterostructure.

It is of great importance to develop useful methods to evaluate interfacial coupling strength noninvasively for exploring and optimizing heterointerface functionality. Recently, organic-inorganic van der Waals (vdW) heterostructures (HSs) composed of organic semiconductors and transition-metal dichalcogenides (TMD) have shown great potential for developing next-generation flexible optical, electrical, and optoelectrical devices. Since vdW coupling dominates the property of such a vdW HS, it is crucial to develop a method to evaluate its interfacial coupling strength noninvasively. In this work, by combining electrical force microscopy (EFM) and Raman and photoluminescence spectroscopic measurements, we were able to directly probe the coupling strength between monolayer MoSe2 and a copper phthalocyanine (CuPc) thin film. Especially, we also found a new Raman mode in HS due to the Davydov splitting of the CuPc thin film via strong interfacial coupling between the two materials. This new Raman mode was thus utilized as a probe to reveal the modulation of the coupling strength by changing post-treatment conditions. All of these results indicate that the method developed here is capable of evaluating the coupling strength of the MoSe2/CuPc HS effectively and innovatively, which aids in providing deep insights into such hybrid vdW HSs for future optical and optoelectrical applications.

Optical, electrical, and gas sensing properties of chloroaluminium phthalocyanine thin film

In this research work, the optical, electrical, and gas sensing properties of Chloroaluminium Phthalocyanine (ClAlPc) thin film have studied. We fabricated sandwich devices of ClAlPc with aluminium electrodes as Al/ClAlPc/Al, using evaporation deposition method in our Laboratory. SEM analysis was carried out to determine the morphology, grains size and thickness of ClAlPc thin film. UV–vis analysis of thin film indicated B and Q absorption bands of ClAlPc, and its optical band gap was then calculated 3.24 eV. The current-voltage characteristic (I-V) of sandwich devices at different temperatures proved the ohmic and SCLC processes in the ClAlPc thin film. By plotting the LnI versus 1000/T graph, the electrical band gap of ClAlPc was obtained 2.88 eV.In the finally section, the gas sensing behavior of sandwich devices in the presence of CO2 was investigated. To determine the temperature of maximum sensitivity (Tmax), the devices were exposed to CO2 gas over the temperature range 300−450 K at a fixed voltage. We found that Tmax =360 K.

Effect of annealing on the optical, structural and electrochromic properties of vacuum evaporated manganese phthalocyanine thin films

Thin films of Manganese Phthalocyanine (MnPc) were thermally deposited onto glass substrates and were vacuum annealed at different temperatures in steps of 50 K. Variation of the optical band gap with annealing temperature was studied for the MnPc thin films from its absorption spectra. Structural properties of the annealed MnPc thin films studied using X Ray diffraction technique yielded grain size for each annealing temperature. Cyclic voltammetry studies showed that all the MnPc thin films changed their color between green-purple-green under different redox potentials and the films annealed at 423 K had the highest electrochemical reversibility and coloration efficiency compared to the other annealed films.

Alkyl chain length dependence of carrier transport in solution-processed phthalocyanine thin films evaluated via MIS-CELIV method

The carrier transport characteristics of 1,4,8,11,15,18,22,25-octaalkylphthalocyanine (CnPcH2) thin films have been investigated by utilizing metal–insulator–semiconductor charge extraction by the linearly increasing voltage method. As the alkyl chain length of CnPcH2 increased from n = 5 to 8, the estimated hole mobility decreased by almost one and a half order of magnitude in the range of 10−4 to 10−5 cm2 V−1 s−1. Furthermore, the relationship between the alkyl chain length and site energy distribution in solution-processed phthalocyanine thin films was investigated. The temperature and field dependences of the hole mobility were analyzed using the Gaussian disorder model, and the effect of the alkyl chain length was discussed by taking the enlargement of the energetic width of the hopping site and the distribution of the hopping distance into consideration.

Exploring the temperature-dependent hole-transport in vanadyl-phthalocyanine thin films

In this paper, the dc electrical properties of Vanadyl phthalocyanine (VOPc) thin films were explored in a hole-only device configuration: ITO/MoO3/VOPc/MoO3/Al. The fabricated diode device was investigated using current density-voltage (J-V) characteristics by varying the substrate temperature from 303 K to 373 K with an interval of 5 K. The barrier height at the ITO/VOPc interface was observed to be reduced from 500 meV to 428 meV as temperature increases. The electrical conduction mechanism was found to be space charge limited currents with exponential trap distribution. Further, the hole-mobility was realized to increase from 1.7 × 10−7 cm2V−1s−1 to 1.2 × 10−5 cm2V−1s−1 (2 orders) with a rise in temperature from 303 K to 373 K. The effective trap density in our device was estimated as Nt ~5.5 × 1022 m−3. However, the improved hole-mobility with temperature is attributed to the enhanced injection of charge carriers (thermally generated) along with the reduction of barrier height.

Polymorphism and structure formation in copper phthalocyanine thin films.

Many polymorphic crystal structures of copper phthalocyanine (CuPc) have been reported over the past few decades, but despite its manifold applicability, the structure of the frequently mentioned α polymorph remained unclear. The base-centered unit cell (space group C2/c) suggested in 1966 was ruled out in 2003 and was replaced by a primitive triclinic unit cell (space group P 1). This study proves unequivocally that both α structures coexist in vacuum-deposited CuPc thin films on native silicon oxide by reciprocal space mapping using synchrotron radiation in grazing incidence. The unit-cell parameters and the space group were determined by kinematic scattering theory and provide possible molecular arrangements within the unit cell of the C2/c structure by excluded-volume considerations. In situ X-ray diffraction experiments and ex situ atomic force microscopy complement the experimental data further and provide insight into the formation of a smooth thin film by a temperature-driven downward diffusion of CuPc molecules during growth.

Direct observation and evolution of electronic coupling between organic semiconductors

The electronic wave functions of an atom or molecule are affected by its interactions with its environment. These interactions dictate electronic and optical processes at interfaces, and is especially relevant in the case of thin film optoelectronic devices such as organic solar cells. In these devices, charge transport and interfaces between multiple layers occur along the thickness or vertical direction, and thus such electronic interactions between different molecules---same or different---are crucial in determining the device properties. Here, we introduce an in situ spectroscopic ellipsometry data analysis method called differential analysis in real time (DART) with the ability to directly probe electronic coupling due to intermolecular interactions along the thickness direction using vacuum-deposited organic semiconductor thin films as a model system. The analysis, which does not require any model fitting, reveals direct observations of electronic coupling between frontier orbitals under optical excitations leading to delocalization of the corresponding electronic wave functions with thickness or, equivalently, number of molecules away from the interface in C60 and MeO-TPD deposited on an insulating substrate $(\mathrm{Si}{\mathrm{O}}_{2})$. Applying the same methodology for C60 deposited on phthalocyanine thin films, the analyses shows strong, anomalous features---in comparison to C60 deposited on $\mathrm{Si}{\mathrm{O}}_{2}$---of the electronic wave functions corresponding to specific excitation energies in C60 and phthalocyanines. Translation of such interactions in terms of dielectric constants reveals plasmonic type resonance absorptions resulting from oscillations of the excited state wave functions between the two materials across the interface. Finally, reproducibility, angstrom-level sensitivity, and simplicity of the method are highlighted showcasing its applicability for studying electronic coupling between any vapor-deposited material systems where real-time measurements during thin film growth are possible.

Effect of organic solvent vapor treatment on transistor performance and contact resistance of copper phthalocyanine based organic field-effect transistors

In this study, we investigated the effect of organic solvent drop-casting and solvent vapor annealing (SVA) on the surface morphology of copper phthalocyanine (CuPc) thin film and its effect on contact resistance in organic field effect transistors (OFETs). Organic solvents: acetone and isopropyl alcohol (IPA) are used for drop-casting and SVA treatment of CuPc film. The morphology, crystallinity and optical properties of untreated and treated CuPc films are investigated through ultraviolet–visible (UV–Vis) absorption spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). The results reveal that crystallinity and grain size increase in CuPc film treated with SVA. Large grain size results fewer grain boundaries forming better contact between source/drain (S/D) electrodes and the organic layer. As a result, the SVA treated CuPc based OFETs show one order increased charge carrier mobility and two order decreased contact resistance compared to that observed in untreated CuPc based OFET.

Temperature-dependent phase composition of fluorinated zinc phthalocyanine thin films and their sensing properties towards gaseous NO2

This work presents a temperature-dependent phase composition study of thin films (200 nm) of fluorinated zinc phthalocyanines (4F, 16F) and their chemiresistive response towards NO2 gas.

Spectral-kinetic properties of transient absorption of hybrid silver–copper phthalocyanine nanostructures

In this paper, we studied the dynamics of transient absorption spectra of a hybrid nanostructure (Ag–CuPc)6 Ag based on island silver films and copper phthalocyanine thin films, as well as individual structural units of this system, by femtosecond transient absorption spectroscopy. It is found that the effects observed for a hybrid nanostructure reflect the existing mutual influence of the plasmonic and organic subsystems on the spectral-kinetic characteristics of each other. The characteristic time of the main component of induced optical density kinetics at a wavelength λ = 525 nm (τ ~ 15 ps) that is caused by singlet-triplet relaxation of the excited electronic states of the organic subsystem of the hybrid structure is noticeably shorter than the relaxation time (τ ~ 50 ps) at the same wavelength for a pure copper phthalocyanine film of 40 nm thickness, just the same as the total thickness of the organic subsystem in the hybrid structure. It is assumed that the presence of silver nanoparticles in the hybrid structure (Ag–CuPc)6 Ag, affects the probability of intersystem conversion in the organic subsystem, accelerating the transition of CuPc molecules to a long-lived triplet state due to a strong local field near the surface of the plasmon particle. The triplet-triplet absorption spectrum of copper phthalocyanine in the spectral range 470–750 nm was obtained.

Passively Q-switched Ytterbium-doped fiber laser using zinc phthalocyanine thin film as saturable absorber

This paper presents a ZnPc: PVA film as saturable absorber (SA) for Q-switched pulse generation at 1-micron region. The SA film was obtained by embedding the ZnPc into polyvinyl alcohol (PVA). It was inserted into an Ytterbium-doped fiber laser (YDFL) cavity to act as a Q-switcher. The Q-switching operation was realized at the center of wavelength of 1036 nm with the minimum pulse width of 2.2 μs. The highest repetition rate and the maximum pulse energy were obtained at 63 kHz and 91 nJ, respectively. A signal to noise ratio (SNR) as high as 49 dB was observed, which indicates a stable operation of Q-switching in the YDFL cavity. This is the first demonstration of the use of ZnPc as Q-switcher in 1-micron wavelength region. A stable and high energy Q-switched pulse was realized with the proposed SA, which was obtained with a low-cost fabrication process.

Molecular orientation and electrical properties in tert‐butylated phthalocyanine thin film fabricated by uniaxial solution coating

AbstractMolecular orientation, molecular packing structure, and electrical properties of thermally stable phthalocyanine, tert‐butylated phthalocyanine (t‐BuPcH2) in the thin film fabricated by bar‐coating method were investigated. The XRD patterns indicated that the columns composed of t‐BuPcH2 molecules formed hexagonal structure, the axis of which was parallel to the bar‐sweep direction, and t‐BuPcH2 molecules were vertically aligned to the bar‐sweep direction. Uniaxially oriented thin films of t‐BuPcH2 were successfully fabricated on Si substrate covered with polyimide by bar‐coating method, and the field effect mobility of t‐BuPcH2 was estimated to be 1.32 × 10−4 cm2 V−1 s−1 at maximum. The field effect mobility parallel to the bar‐sweep direction was approximately three times higher than that perpendicular to the bar‐sweep direction due to high electrical conduction along the column axis of t‐BuPcH2.

Molecular Orientation and Electrical Properties in <i>tert</i>-Butylated Phthalocyanine Thin Film Fabricated by Uniaxial Solution Coating

Molecular Orientation and Electrical Properties in <i>tert</i>-Butylated Phthalocyanine Thin Film Fabricated by Uniaxial Solution Coating

Pump-Probe Technique to Study of the All-Optical Switching Properties of Copper Phthalocyanine Thin Film prepared via Pulsed laser deposition

Z-scan has been utilized for studying the non-linear properties and optical limiting behaviors of the dye Copper Phthalocyanine thin films. The refractive index is negative, which indicates a self-defocusing behavior and non-linear absorption coefficient (β) of CuPc is a positive sign is a result of RSA. The optical switching behaviors of dye have been researched with the use of the method of the pump-probe with 9ns Q-Switched Nd: YAG laser at pump beam equal to 532 nm and a probe beam equal to 630nm Diode laser. The thin films of copper Phthalocyanine also reflect a significant limiting of the optical power of CW laser with an adequate threshold of the optical limiting. The dye’s switching behavior is a result of the probe beam’s excited-state absorption (ESA) with the molecules of the dye. The modulation of the probe beam with the increase of intensity of the pump has been researched as well.

The electric field at the hole-injecting metal/organic interface controls the bias dependence of the current–voltage hole mobility

Based upon the room temperature current–voltage data of some published organic diode structures the unique phenomenon of the decreasing hole mobility, μ, with the increasing applied electric field, E a, is interpreted. The measurable quantity, the hole drift mobility μ d is formulated in terms of E a and the electric field at the hole injecting metal/organic interface, E int, dependent algebraic function multiplied by the intrinsic hole mobility, μ max that is organic morphology dependent but E a independent scaling factor. On account that the intrinsic mobility, μ max, is uncoupled from both E a and E int it is shown that the origin of the negative field hole mobility effect occurs due to E int, that is a linear function of E a. The bias and the space distribution of the internal organic electric field, E, as well as the free hole density, p, for poly(3-hexylthiophene) is calculated in detail. Depending on the organic layer morphology the internal electric field may exhibit, at the particular value of E a, a deep well in the vicinity of the hole injecting metal/organic interface. Then the strong peak of the free hole density exists there the effect of which is spreading some 10 nm into the organic. If E int happens to be E a independent constant, then from the resulting space charge limited current density, the increasing hole drift mobility, μ d, with the increasing applied electric field, E a, is deduced. The published current–voltage data of two distinct metal-substituted phthalocyanine thin films provide an additional confirmation of the described formalism.

Morphological and optical properties of α- and β-phase zinc (∥) phthalocyanine thin films for application to organic photovoltaic cells.

We have investigated the morphological and optical properties of α- and β-phase Zinc Phthalocyanine (ZnPc) thin films for application to organic photovoltaic cells (OPVs). It was found that the α-phase is completely converted to the β-phase by thermal annealing at 220 °C under ultrahigh vacuum conditions. When the α- to β-phase transition takes place, the surface roughness of the ZnPc film became flat uniformly with a nanometer order of unevenness by anisotropic growth of crystalline grains along a lateral direction to substrates. Correspondingly, the optical absorbance of the β-phase film became greater by 1.5-2 times than that of the α-phase one in an ultraviolet-visible-near infrared (UV-vis-NIR) wavelength range, which plays a role in increasing the number of photogenerated excitons. On the contrary, time-resolved photoluminescence measurements showed that the average lifetime of excitons for the β-phase film became shorter by 1/6-1/7 than that for the α-phase one, which plays a role in decreasing the number of excitons achieving the donor/acceptor interface where excitons are separated to carriers (holes and electrons). Both the increase in the number and the shortening in the average lifetime have a trade-off relationship with each other for contribution to the photoelectric conversion efficiency of OPVs. Then, we examined an external quantum efficiency (EQE) of OPVs using the α- and β-phase films as a donor and obtained that the former OPV (α-phase) exhibits a higher EQE by ∼2 times than the latter one (β-phase) in the wavelength range of 400 nm-800 nm.

Growth of Cu phthalocyanine thin films on Sb passivated vicinal Si(111) with molecular columns parallel to the surface

This study shows a growth of copper phthalocyanine (CuPc) thin films with one-dimensional structures parallel to the surface on Sb-passivated stepped silicon surfaces with (111) orientation. Sb passivation maintains all the step and terrace features on the vicinal Si(111) surface, where subsequently a CuPc sub-monolayer is deposited. The CuPc forms islands of sub-micrometer extension, which shows substantial molecular diffusion on the surface after deposition. In a single island of CuPc, one-dimensional columns of stacked CuPc molecules grow parallel to the step edges of the vicinal Sb–Si(111) surface, which illustrates the strong anisotropy of molecular growth induced by the stepped surface. The self-assembly behavior of CuPc indicates that the Sb passivated surface allows high molecular mobility of CuPc, having anisotropy effect from the stepped substrate structure.

Chipless RFID Tag With Enhanced RCS Used as a Phthalocyanine-Based Solvent Vapors Sensor

A novel uniplanar chipless RFID solvent vapors/gas sensor is proposed in this letter. The sensor etched on an extremely thin capton substrate is composed of the folded dipole resonator loaded by the interdigital capacitor located inside the planar rectangular metallic loop that improves the radar cross section (RCS) response. When illuminated by a plane wave, the folded dipole causes a notch in the RCS response of the loop located near its resonant frequency. The high RCS level (-18 dBsm), together with the notch depth (16 dB) assure a reliable detection of its position within the frequency dependence of RCS curve. In order to enhance the structure sensitivity to the presence of acetone vapors, the tetrasulfonated copper phthalocyanine thin film was applied as a sensitive layer during the process of folded dipole metallization. The experimental verification confirmed the viability of sensor proof-of-concept for the detection of chemical vapors.

Investigate the Structural and Optical Properties of Nickel Phthalocyanine (NiPc)Thin Films Prepared by Chemical Spray Pyrolysis Method.

The technique of the chemical spray pyrolysis has been employed to deposit Nickel Phthalocyanine (NiPc) on different substrate types at temperatures 150 °C to investigate their structural, Scanning Electron Micrographs, X-ray diffractograms and optical properties. The results of X-ray diffraction show that structure of the powder is polycrystalline with monoclinic structure, and the results of XRD for a thin film of NiPc shows polycrystalline with a fairly weak degree of crystallization, SEM revealed that the surface of the film is usually homogeneous, the roughness of NiPc films was evaluated by AFM technique and the results showed that the grain size increases with increasing of concentration. The optical measurement using UV-Visible Spectra showed that the NiPc thin films have an optical constant like the absorption coefficient and have a direct energy gap for all samples.