Copper Phthalocyanine Films Research Articles

Study of the Effect of Thin Layer Thickness on the Structural Properties of Copper Phthalocyanine (CuPc) Films Prepared by Vacuum Thermal Evaporation Method

Study of the Effect of Thin Layer Thickness on the Structural Properties of Copper Phthalocyanine (CuPc) Films Prepared by Vacuum Thermal Evaporation Method

Solution-processed filamentous copper phthalocyanine films for enhanced NO2 gas sensing at room temperature

Here, the facile strategy of preparing filamentous copper phthalocyanine (CuPc) based gas sensors using a solution method was studied. Electrical and gas sensitive properties of filamentous CuPc films transistors were studied in detail.

Ordering of copper phthalocyanine films on functionalized Si(111)

The adsorption and growth of copper phthalocyanine (CuPc) has been studied on passivated Si(111) surfaces. As passivating agents, Ga, Bi, and Ag were used, leading to a 3×3-R30∘ reconstruction of the surface in each case. X-ray photoemission spectra indicate a non-dissociative adsorption. The structure and morphology have been investigated with low-energy electron diffraction and scanning tunneling microscopy. For Ga-terminated substrates, ordered domains are observed with random azimuthal orientation. Upon further deposition, three-dimensional islands are found. In case of Bi-terminated Si(111), a rather smooth morphology with high structural disorder evolves, which is attributed to an inefficient surface diffusion. The CuPc films with best structural order, with a nearly square unit mesh, and with smooth morphology are achieved on Ag-terminated Si(111). The differences in structural and morphological evolution of the CuPc films for Ga, Bi, and Ag surface passivation are discussed in terms of interfacial interaction and occupied versus unoccupied local density of states.

Structural, morphological and photoluminescence studies on annealed Langmuir-Blodgett films of copper and zinc octakis-octyloxy phthalocyanine and their mixture

Langmuir-Blodgett films of copper(II) 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (CuPcOC8) and zinc 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (ZnPcOC8) and their mixture, CuPcOC8/ZnPcOC8 (1:1) at the air-solid (A-S) interface have been investigated using grazing incidence X-ray diffraction (GIXD), atomic force microscope (AFM), UV–visible absorbance and photoluminescence techniques. At the A-S interface, the GIXD pattern reveals the crystalline nature of the as-deposited and annealed LB films of CuPcOC8. The Bragg peak observed at 3.4° (d = 25.9 Å) for the as-deposited and annealed film (323 K) tends to shift to a higher angle (3.8°, d = 23.2 Å) at higher temperature (>373 K). Though the absence of Bragg peak in the as-deposited film of ZnPcOC8 suggests an amorphous phase, annealing at 323 K results in a Bragg peak at 3.4° which shifts to a higher angle (3.6°, d = 24.5 Å) at higher temperatures (>373 K). The mixed film also exhibited a Bragg peak at 3.4° which shifts to 3.6° with annealing. Surface topographies obtained using AFM reveal nanowire morphology for the as-deposited film of CuPcOC8 whereas a grainy texture is observed for ZnPcOC8. Upon annealing to 373 K, the coexistence of nanowire with thin crystalline flakes for CuPcOC8 and the coexistence of needle-like structures with granular features for ZnPcOC8 were observed. The topography of the as-deposited and annealed (till 373 K) films of the mixture shows the coexistence of two different morphologies (needle and granular, d = 25.9 Å) which on further annealing (>373 K) transforms to granular morphology (d = 24.5 Å). The UV–visible absorbance studies show the presence of B-bands and Q-bands for the as-deposited films of CuPcOC8, ZnPcOC8 and their mixture. Photoluminescence studies show a clear dependence of emission features with different excitation wavelengths for the as-deposited and annealed films of CuPcOC8, ZnPcOC8 and their mixture. The spectral features for these systems were deconvoluted to obtain the peak parameters at 300 nm excitation. Combining the results obtained using the above mentioned techniques, we infer the occurrence of Form-I polymorph (as-deposited and at 323 K), the coexistence of polymorphs (Form-I and Form-II) at 373 K and Form-III above 373 K for CuPcOC8. For the case of ZnPcOC8, though the spectral features for the as-deposited and annealed films (>373 K) were quite similar, GIXD and AFM results seem to suggest amorphous phase and Form-III polymorph. The new emissions in the blue region observed at 323 K and 373 K is attributed to the presence of Form-I and coexisting polymorphs (Form-I and Form-II). For the mixture, we infer a solid-solid phase separation (below 373 K) and a new crystalline polymorph (above 373 K). Our studies highlight how thermal annealing can modify the structure, packing, morphology of the thin film polymorphs and impact the optical properties.

Tuning Organic Semiconducting Binary Heterostructures Inherited by Template Nanostructures for Achieving High‐Performance Organic Transistors

AbstractThe charge transport in organic semiconductors is unavoidably affected by morphological or crystalline structure resulting from the self‐organized polycrystalline characteristics. To obtain the desired molecular arrangement in the heterostructured active layer, where nanostructures are gradually formed by piecing individual parts together into the final structures, it is necessary to formulate a precise strategy for anisotropic formation via weak epitaxy growth (WEG) of the layer structures. This strategy includes the nanostructural control of the bottom‐templating layer through the inert character optimization of the supporting substrate surfaces. For these purposes, a copper phthalocyanine (CuPc) film grown on p‐sexiphenyl (p‐6P) as a bottom‐templating layer is prepared to induce WEG between them, and supporting substrates are controlled using various inert self‐assembled interlayers. The grain structures of the bottom‐templating p‐6P layer are dependent on the polar term of the surface energy in the variously modified supporting substrate, thereby inducing the activated WEG effect between the p‐6P and CuPc semicrystalline structures. This strategy significantly improved the device performances of CuPc transistors (by a factor of up to 14). This result has important implications for optimizing a heterostructured active layer induced by the WEG mechanism and provides a solution for improving the device performance of organic electronics.

Gold atom diffusion assisted thermal healing enabling high-performance hole-transporting material in solar cells

The use of the compact hole-transporting layer (HTL) with strong hole extraction ability is vital to prepare high-efficiency solar cells. Here, we report the application of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) doped copper phthalocyanine (CuPc) as the hole-transporting layer for the Sb2(S,Se)3 solar cells. We find that the diffusion of gold atoms into the copper phthalocyanine film is able to heal the cracks and pinholes of the CuPc film, which enables the morphology to become more flat and denser, along with enhanced hole mobility. Benefitting from these results, the F4-TCNQ doped CuPc-based Sb2(S,Se)3 solar cells achieved best power conversion efficiency of 8.57%. More importantly, the device based on F4-TCNQ doped CuPc HTL showed essentially improved operational stability under the condition of 85% humidity and 85 °C. This research provides a suitable method for improving the morphology and transport properties of the CuPc based hole-transporting layer for solar cell and other optoelectronic device applications.

High‐Performance Ultrathin Molecular Rectifying Diodes Based on Organic/Inorganic Interface Engineering

AbstractThe bottom‐up engineering of organic/inorganic hybrids is a crucial step toward advanced nanomaterial technologies. Understanding the energy level alignment at hybrid interfaces provides a valuable comprehension of the systems′ electronic properties – which are decisive for well‐designed device applications. Here, active interfaces of ultrathin (≈10 nm) molecular rectifying diodes that are capable of achieving a 4‐order‐magnitude rectification ratio along with 10 MHz cutoff frequency, both in a single nanodevice, are engineered. Atomic force microscopy and Kelvin‐Probe analysis are employed to investigate the surface potential of the hybrid devices′ organic/inorganic interfaces, which comprise a metal (M) electrode in contact with a few‐nanometer‐thick copper phthalocyanine (CuPc) film. Thereby a nanometer‐resolved quantification of the CuPc film work functions as well as the M/CuPc diode's space‐charge densities are delivered. By recognizing that the molecular rectifying diode is a functional building block for nanoscale electronics, the findings address crucial advances to the design of high‐performance molecular rectifiers based on organic/inorganic interface engineering.

Thin film growth of phase-separating phthalocyanine-fullerene blends: A combined experimental and computational study

Blended organic thin films have been studied during the last decades due to their applicability in organic solar cells. Although their optical and electronic features have been examined intensively, there is still lack of detailed knowledge about their growth processes and resulting morphologies, which play a key role for the efficiency of optoelectronic devices such as organic solar cells. In this study, pure and blended thin films of copper phthalocyanine (CuPc) and the Buckminster fullerene (C60) were grown by vacuum deposition onto a native silicon oxide substrate at two different substrate temperatures, 310 K and 400 K. The evolution of roughness was followed by in-situ real-time X-ray reflectivity. Crystal orientation, island densities and morphology were examined after the growth by X-ray diffraction experiments and microscopy techniques. The formation of a smooth wetting layer followed by rapid roughening was found in pure CuPc thin films, whereas C60 shows a fast formation of distinct islands at a very early stage of growth. The growth of needle-like CuPc crystals loosing their alignment with the substrate was identified in co-deposited thin films. Furthermore, the data demonstrates that structural features become larger and more pronounced and that the island density decreases by a factor of four when going from 310 K to 400 K. Finally, the key parameters roughness and island density were well reproduced on a smaller scale by kinetic Monte-Carlo simulations of a generic, binary lattice model with simple nearest-neighbor interaction energies.

Changes in the Electronic Structure of Tetra-Tert-Butyl Copper Phthalocyanine Film by Ultraviolet-Ozone Treatment

Changes in the Electronic Structure of Tetra-Tert-Butyl Copper Phthalocyanine Film by Ultraviolet-Ozone Treatment

Bilayer polymer dielectric systems for high response NO2 gas sensors

In this study, the effects of bilayer polymer dielectric systems on the characteristic of nitrogen dioxide (NO2) gas sensors and organic field effect transistor (OFET) were investigated. Different bilayer polymer dielectrics were obtained by depositing polymethyl methacrylate (PMMA) films on monolayer polystyrene (PS), polyvinyl pyrrolidone (PVP), or PMMA films by spin coating. The responsivity of PS/PMMA-based sensors to 30 ppm NO2 gas is up to 7633%, which is 35.7% higher than that of PMMA/PMMA-based sensors. Meanwhile, the sensitivity to NO2 gas has increased from the lowest 191%/ppm to 265%/ppm. The copper phthalocyanine (CuPc) film on PS/PMMA dielectric layer is induced to form more gaps between the rod domains, which are favorable to the gas interaction. The response mechanism was proposed that the equivalent three-dimensional sensing films caused by multi-layer polymer dielectrics play a significant role in the remarkable increase of gas response.

Photoresponse characteristics from vacuum deposited thin film of copper phthalocyanine: dependence on grain size

An organic photodetector (PD) is fabricated with single layer thin film of copper phthalocyanine (CuPc) on glass substrate. The thermal deposition of CuPc film on the substrate was realized under high vacuum and at different substrate temperature (room temperature, 40 ◦C, 70 ◦C, 100 ◦C). The comparison of photoresponse characteristics of CuPc thin film deposited under different conditions showed good improvement with increase in the substrate temperature, and the best performances being observed for the film deposited at substrate temperature of 100 ◦C. The thin film of CuPc characterized through X-ray diffraction (XRD) spectroscopy and atomic force microscopy (AFM) clearly indicated that with increase in substrate temperature, the grain size of CuPc film increased, which improved the crystallinity and hence the photoconductivity of the device. The CuPc thin film based PD displayed stable and reproducible photoswitching characteristics under white light irradiation, with photocurrent modulation by varying in input optical power. The highest photo to dark current ratio and responsivity of the devices was calculated to be, ca. 6.5 and 7.1 mA-W−1 at low optical power, ca. 14.5 mW-cm−2.

Influence of molecular stacking pattern on excited state dynamics of copper phthalocyanine films

Photophysical processes occurring within organic semiconductors is important for designing and fabricating organic solar cells. Copper phthalocyanine (CuPc) is a typical electron acceptor. In this work, the triplet exciton lifetime is prolonged by altering the molecular stacking pattern of the CuPc film. For CuPc thin films, the excited state decays are mainly determined by the triplet-triplet annihilation process. The ultrafast transient absorption measurements indicate that the primary annihilation mechanism is one-dimensional exciton diffusion collision destruction. The decay kinetics show a clearly time-dependent annihilation rate constant with γ∝t−1/2. Annihilation rate constants are determined to be γ0 = (2.87±0.02)×10−20 cm3·s−1/2 and (1.42±0.02)×10−20 cm3·s−1/2 for upright and lying-down configurations, respectively. Compared to the CuPc thin film with an upright configuration, the thin film with a lying-down configuration shows longer exciton lifetime and higher absorbance, which are beneficial to organic solar cells. The results in this work have important implications on the design and mechanistic understanding of organic optoelectronic devices.

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.

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.

MACROCYCLE RING AND PERIPHERAL GROUP SIZES-DEPENDENT VAPOR SENSING PROPERTY OF COPPER PHTHALOCYANINE THIN FILMS

Spin-coated thin films of copper phthalocyanine (CuPc) were fabricated using different rotation speeds from 250 rpm to 1250 rpm. The structural characterization of these films was analyzed using UV-vis spectroscopy and atomic force microscopy (AFM). Gas sensing properties of these spun thin films were investigated against different volatile organic compounds such as chloroform, dichloromethane and toluene using surface plasmon resonance (SPR) technique. CuPc thin films were found to be highly sensitive to chloroform and dichloromethane vapor with fast response and recovery times. These measurements clearly indicated that the CuPc molecule is a promising material for the development of the room temperature vapor sensing applications with sensitivities between [Formula: see text] and [Formula: see text] percent response ppm[Formula: see text]. Three different functional groups of CuPc structures coded as CuPc I, II and III were investigated which differ from each other in their chemical structures in terms of their microcycle ring groups and peripheral groups, all attached to the same free base porphyrin skeleton. The number of microcycle ring groups and peripheral groups were found to be efficient on the gas sensing properties. The calculated refractive index and extinction coefficients using SPR curves were [Formula: see text] for CuPc I thin film, [Formula: see text] for CuPc II thin film and [Formula: see text] for CuPc III thin film, respectively. For different substrate rotation speeds, the thin film thicknesses vary between 2[Formula: see text]nm and 6[Formula: see text]nm for CuPc I and CuPc III thin films whereas it ranges between 4[Formula: see text]nm and 9[Formula: see text]nm for CuPc II thin film.

Effect of Annealing Induced Morphology on Mobility of Copper Phthalocyanine Thin Films

Post deposition annealing of copper phthalocyanine (CuPc) films develops nano-rod structures on the surface of the film and the length and uniformity of nano-rods depend on the annealing temperature. The proposed methodology combines scanning electron microscopy (SEM) and atomic force microscopy (AFM) with impedance spectroscopy to give new insights into the influence of thermally developed nano structures on the charge carrier mobility of CuPc films. The impedance spectroscopy provides a non-invasive and cost-effective study which finds that the hole mobility of CuPc films improves upon increasing annealing temperature, reaches maximum of (5.3 ± 0.7) × 10–5 cm2V−1 s−1 at 150 °C and reduces at higher temperatures. These results will benefit future strategies for the surface modification of small molecular films for improved charge transport in organic and hybrid devices.

Thin films of copper phthalocyanine deposited by solution processing methods

Abstract In this work, we show and discuss the surface structure picture of copper phthalocyanine (CuPc) thin films deposited from trifluoroacetic acid (TFA) solvent onto silicon substrates at ambient conditions by four solution processing methods, namely drop-casting, dip-coating, spin-casting and spray-coating. The CuPc films were studied by AFM, as the main technique, and complemented by micro-Raman spectroscopy. Essentially, such thin films consist of CuPc molecular nanoribbons of a fixed ~1 nm thickness. CuPc molecules are arranged in an in-plane direction and formed in stacks under a defined tilt angle with respect to the substrate surface (monolayer) or underlying CuPc layer (multilayer). The film morphology takes various forms depending on the solution concentration, number of layers, and the deposition method. For instance, the morphology varies from very wide (~600 nm) but flat (~1 nm) ribbons for films prepared by dip-coating to crystallized rod-like features (multi-layered ribbons) when obtained by spray-coating. The factors studied in this paper should be taken into consideration in designing and controlling the criteria for rigorous CuPc film architecture.

Study of Desorption Products under Laser Irradiation of the Surface of Organic Films

The paper presents the results of mass spectrometric studies of laser-stimulated desorption from the surface of thin films based on organic copper phthalocyanine molecules with peripheral substituents on gallium arsenide substrates. Thin films (30-80 nm) of copper phthalocyanine with peripheral substituents in this regard are studied for the first time. The composition of particles desorbed from the surface of CuPc and CuPcF16 films by laser radiation of various wavelengths of 532 nm and 1.06 μm with a pulse duration of 10 ns was studied. The identification of the main fragments of molecules present in the desorption stream was carried out. It was shown that under the action of laser radiation, the surface is leveled and the films are fragmented, followed by desorption of molecular fragments.

Noble metal nanoparticles in organic matrix

The purpose of this work is the synthesis and study of the properties of nanocomposite structures created by noble metal (silver) nanoparticles (NP's), an exciting class of materials with unique properties differ from both bulk and atomic behavior, which are self-organize in a thin organic film of copper phthalocyanine (CuPc). The structure and morphology of this material, depending on the amount of deposited silver, was studied in ultrahigh vacuum using transmission electron microscopy (TEM) and photoelectron spectroscopy (PES). Metallic atoms deposited on the surface of an organic substrate diffuse into the substrate, forming NPs with a narrow size distribution, which correlates with the content of the deposited metal. With the help of high-resolution TEM, the distance between the atomic planes of individual silver nanoparticles was determined and the steady gathering of individual nanoparticles into agglomerates and then into nanocrystals with inter-crystallite boundaries was observed. PES revealed a generally weak interaction between silver NPs and the organic matrix. However, a strong band bending in the organic film at small coatings with metal atoms was observed.

The scanning probe microscopy of the structural, elastic and conductive properties of two-component phthalocyanines

Thin films of two-component H2Pc, PdPc, PbPc, CuPc phthalocyanines were studied by scanning probe microscopy methods. Young’s modulus values of the phthalocyanines films were measured, which made it possible to optimize the regimes for studying soft phthalocyanine films and to select suitable probes with proper stiffness and the magnitude of the force acting onto the surface. For all films, the electric field induced reversible local conductivity switching effect was studied. It is shown that under room conditions it is possible to reversibly change the value of the local conductivity of a copper phthalocyanine film approximately by an order of magnitude. When conducting the experiment under vacuum conditions, a significant weakening of this effect occurs. It has been established that for a CuPc film, a pressure of 20 mbar is the lower boundary value for creating regions of increased conductivity. The observed effect is explained by the penetration of OH− ions (from the surface adsorbed water film) into the phthalocyanine film with the subsequent formation of oxygen-containing complexes that increase conductivity.