CuPc 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.

Non-linear optical studies of CuPc

Thin films of Copper Phthalocyanine CuPc of various thicknesses (150, 300 and 450) nm have been deposited using pulsed laser deposition technique using Q – Switched Nd:YAG laser pulse at 1.64 μm wavelength, 6 Hz frequency, 9 ns width, and 240 mJ energy at room temperature. The study showed that the spectra of the optical absorption of the thin films of the CuPc are two bands of absorption one in the visible region at about 635 nm, referred to as Q-band, and the second in ultra-violet region where B-band is located at 330 nm. CuPc thin films were found to have direct band gap with values around (1.81 and 3.14) eV respectively. The vibrational studies were carried out using Fourier transform infrared spectroscopy (FT-IR). Finally, from open and closed aperture Z-scan data non-linear absorption coefficient and non-linear refractive index have been calculated respectively using He-Ne laser which have beam waist of (24.2 μm), wave-length of (632.8 nm) and Rayleigh thickness was 2.9 mm.

The effect of depositions parameters on the nanostructural and optical properties of CuPc organic thin films growth by oblique angle deposition CSP technique

Organic semiconductor CuPc thin films were deposited on different substrates with OAD CSP technique. The effects of substrate type, glancing angle and deposition temperature on surface and structural properties of CuPc thin films was reported in this study. The structural and morphological properties of CuPc thin films were investigated by XRD, RAMAN and FEG-SEM analysis. Dendritic nanostructures and nanoporous-straticulate sponge like structures were determined at surface area of CuPc thin films. XRD patterns showed that these CuPc thin films have orthorhombic α-phase structure with 2θ peak at 6.89˚, which is %100. The optical properties of all CuPc films which were determined from transmittance and reflectance measurements. The increasing of spray glancing angle and substrate temperature were decreased the UV-VIS absorption intensities at S-band and Q-band. However at 200 °C and 250 °C deposition temperatures at 45° spray glancing angle affected the Q-band absorption acerbically and red shift observed in here.

Cu-phthalocyanine long-range ordered bulk growth due to the weak interaction with highly oriented pyrolytic graphite substrate

We investigate the relationship between the ordered growth of copper-phthalocyanine (CuPc) on highly oriented pyrolytic graphite (HOPG) and the electronic interaction at the interface. Via spot profiles analysis of electron diffraction patterns we determine an ordered growth for all measured CuPc films ranging from sub-monolayer to 3.3 nm. In particular we found that for CuPc thick films the ordered domains have a dimension of 50 nm. Electronic structure of CuPc/HOPG interface was studied by means of photoelectron and electron energy loss spectroscopies (EELS). From photoelectron spectroscopy we observe that molecules at the interface are weakly physisorbed. This weak interaction contributes to the formation of ordered 2-D islands. Since the geometry of the surface unit cell does not change with film thickness, the second CuPc layer grows stacked flat on the first one, forming ordered 3-D islands. It follows that the ordered bulk phase derives from the weak interaction between Pcs and HOPG. The Q band of CuPc/HOPG, measured via EELS, is different from the ones of the most common Pc phases. Therefore, electron diffraction and EELS measurements indicate the formation of a novel Pc long-range ordered structure observed only at this interface.

Thin film and surface preparation chamber for the low energy muons spectrometer

We have designed and constructed a thin film preparation chamber with base pressure of <2×10−9 mbar. Currently, the chamber is equipped with two large area evaporators (a molecular evaporator and an electron-beam evaporator), an ion sputtering gun, a thickness monitor and a substrate heater. It is designed such that it can handle large area thin film samples with a future possibility to transfer them in vacuum directly to the low energy muons (LEM) spectrometer or to other advanced characterization facilities in the Quantum Matter and Materials Center (QMMC) which will be constructed in 2024. Initial commissioning of the chamber resulted in high quality, large area and uniform molecular films of CuPc and TbPc2 on various substrate materials. We present first results from low energy µSR (LE-µSR) measurements on these films.

Nanoscale-Thick CuPc/β-Ga2O3 p–n Junctions for Harsh-Environment-Resistant Self-Powered Deep-UV Photodetectors

Due to their crucial role in ultraviolet communication and monitoring, deep-ultraviolet (DUV) photodetectors have garnered much interest. Recently, Ga2O3 has emerged as the best material for DUV photodetectors because of its ultrawide bandgap (4.5–4.9 eV), excellent UV photon absorption coefficient, high structural stability, and affordability. However, there are several difficulties in realizing high-performance Ga2O3-based DUV photodetectors with a high tolerance for harsh environments. In this work, nanoscale-thick CuPc/β-Ga2O3 p–n junctions were used to build high-performance DUV photodetectors by a straightforward solution-processing approach. The p–n junction photodetectors exhibit improved photoelectric performance compared to a single device made of β-Ga2O3 or CuPc, with a photo-to-dark current ratio of 3700 and a fast response time of ∼20 ms under a bias of 0 V. Due to the excellent stability of the nanoscale-thick CuPc film, the device can maintain a high photocurrent even at high temperatures or under long-term DUV irradiation. Our work provides an effective strategy toward highly harsh-environment-resistant DUV photodetectors.

Improvement in metrological performances of phthalocyanine-based QCM sensors for BTX detection in air through substituent’s effect

Molecular engineering in macrocyclic materials like metallophthalocyanines (MPc) is a powerful strategy to tune the thin film properties that can be relevant to develop high performance gas sensors. In this context, the present work reports the enhancement in BTX sensing properties of MPc-based quartz crystal microbalance (QCM) sensors through exploiting the large surface area of tertiary-butyl (ttb) substituent grafted at the periphery of CuPc. Thin films of CuPc and ttb-CuPc reveal distinct morphologies and microstructures, in which the former presents a locally organized columnar structure, while the latter has an amorphous structure, containing agglomeration of molecular clusters. Such structural variation of the MPc films has huge implications on benzene, toluene and xylenes (BTX) sensing properties of the QCM sensors, utilizing these materials as sensing layers. Responses of ttb-CuPc-based QCM sensor are amplified by ca. 4-times and response time is reduced, compared to CuPc-based sensor. Moreover, ttb-CuPc-based QCM sensor displays high repeatability, resolution better than 20 ppm, negligible hysteresis and high sensitivity with limit of detection to 2 ppm, 1 ppm and 0.7 ppm for benzene, toluene and xylenes, respectively. Such favorable metrological characteristics combined with negligible interference from other gases make this microsensors suitable for BTX detection in real environment at concentrations below the recommended guidelines.

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.

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.

Influence of Temperature on Exciton Dynamic Processes in CuPc/C60 Based Solar Cells.

Although the effect of high temperature on the performance of organic solar cells has been widely investigated, it is inevitably influenced by the associated annealing effect (which usually leads to film morphology change and variation in electrical properties), which makes the discussion more sophisticated. In this study, we simplified the issue and investigated the influence of low temperatures (from room temperature to 77 K) on the photocurrent and internal/external quantum efficiency of a CuPc/C60 based solar cell. We found that besides the charge dynamic process (charge transport), one or more of the exciton dynamic processes, such as exciton diffusion and exciton dissociation, also play a significant role in affecting the photocurrent of organic solar cells at different temperatures. Additionally, the results showed that the temperature had negligible influence on the absorption of the CuPc film as well as the exciton generation process, but obviously influenced the other two exciton dynamic processes (exciton diffusion and exciton dissociation).

The effect of MoO3 interlayer on electro-physical characteristics of the perovskite solar cells

This report shows that sequentially deposited CuPc and MoOx films are an effective hole-transport layer (HTL) for perovskite solar cells (PSCs). PSCs with only CuPc hole-transport layer have a low power conversion efficiency (PCE) of 3.51%, which mostly due to a poor fill factor (FF) of 29.4%. The incorporation of the MoOx interlayer between the CuPc layer and the anode (Ag) significantly boosted device FF and PCE up to 63.2% and 8.12%, respectively. The analysis of the impedance spectra of PSCs indicates that the MoOx interlayer reduces HTL resistance and increases the recombination resistance at the perovskite/HTL interface, which increases an effective charge carrier lifetime. Moreover, MoOx electric transport properties depends on the stoichiometry of the crystal structure, which can be varied by tuning vacuum level during the thermal sputtering of MoOx layers. PSCs based on the MoOx layer deposited at low vacuum (10−2 Pa) have reached PCE of 8.12% owing to the optimization of the interlayer energy levels and electric transport properties of MoOx films. In this work, we have developed the double hole-transport layer (HTL) for PSCs, which can prevent perovskite degradation on perovskite/HTL interface and hinder a severe charge recombination.

Three-dimensional CuPc films decorated with well-ordered PVA parallel nanofiber arrays for low concentration detecting NO2 sensor

Abstract Well-ordered polyvinyl alcohol (PVA) parallel nanofiber arrays (PNAs) were fabricated by using electrospinning receiving board with clined gap. A three-dimensional (3D) copper phthalocyanine (CuPc) organic field effect transistor (OFET) sensor was obtained by evaporating CuPc on the PVA PNAs. This 3D structure is conducive to the multi angle adsorption and desorption of the target gas and active layers. The detection limit of the obtained sensors is lower, and the response and recovery time are also shorter. Compared with single CuPc films and CuPc films with disordered PVA nanofibers sensors, the minimum detection concentration is reduced by one third. The CuPc/PVA PNAs sensors have been successfully used in real-time monitoring of NO2 at 0.3 ppm. The response and recovery time of the CuPc/PVA PNAs sensors are both 0.02 min for 25 ppm NO2. The response and recovery time are 350 and 130 times faster than those of CuPc sensors with disordered PVA nanofibers, respectively. Humidity has little effect on the response of the sensor. This convenient and effective method to prepare high performance OFET sensors can be extended to other gas monitoring.

Structural, surface morphology and optical properties of annealing treated Copper Phthalocyanine doped Fullerene (CuPc: C60) thin films

The doping process with materials related to carbon has become a newly emerged approach for achieving an improvement in different physical properties for the obtained doped films. Thin films of CuPc: C60 with doping ratio of (100:1) were spin-coated onto pre-cleaned glass substrates at room temperature. The prepared films were annealed at different temperatures of (373, 423 and 473) K. The structural studies, using a specific diffractometry of annealed and as deposited samples showed a polymorphism structure and dominated by CuPc with preferential orientation of the plane (100) of (2θ = 7) except at temperature of 423K which indicated a small peak around (2θ = 31) for C60. AFM remarks showed the existence of a compact packing film with a smooth surface. The FTIR spectra emphasized the bonding between CuPc and C60. UV-Vis Absorption spectroscopy confirmed that the CuPc was dominating the optical properties with a small shift in Q band towards higher wavelengths.

Linear and Non-Linear Optical Properties for Organic Semiconductor (CuPc) Thin Films

Thin films of CuPc of various thicknesses (150,300 and 450) nm have been deposited using pulsed laser deposition technique at room temperature. The study showed that the spectra of the optical absorption of the thin films of the CuPc are two bands of absorption one in the visible region at about 635 nm, referred to as Q-band, and the second in ultra-violet region where B-band is located at 330 nm. CuPc thin films were found to have direct band gap with values around (1.81 and 3.14 (eV respectively. The vibrational studies were carried out using Fourier transform infrared spectroscopy (FT-IR). Finally, From open and closed aperture Z-scan data non-linear absorption coefficient and non-linear refractive index have been calculated respectively using He-Ne laser which have beam waist of (24.2 μm), wave-length of (632.8 nm) and Rayleigh thickness was 2.9 mm.

Annealing effect of pentacene and ultrathin metal anode buffer on the performance of small-molecule organic solar cells

The annealing effect of thin pentacene and ultrathin gold/silver anode buffer layers on both the initial performance and durability against repetitive illumination stress in small-molecule organic solar cells (OSCs) was experimentally investigated. The OSC had a structure of indium tin oxide (ITO, anode)/anode buffer/copper phthalocyanine (CuPc, donor)/fullerene (acceptor)/bathocuproine (cathode buffer)/Ag (cathode). OSCs with a 3-nm-thick pentacene anode buffer layer provided a 15% increase in the power conversion efficiency compared to OSCs with no pentacene layer. OSCs with an ultrathin 0.3-nm-thick Au anode buffer layer provided an increase of 63% in durability compared to OSCs without the Au layer. OSCs with the Au layer did not show apparent leakage current, while those with the Ag layer did. OSCs with a combinational anode buffer of the pentacene layer/Au layer were mainly examined. The spatial distribution of Au atoms on pentacene was uniform even after annealing, which helped to improve the quality of CuPc crystals. The ultrathin Au layer brought both a large absorption of ultraviolet (UV) light and highly dense nucleation sites for overlaid CuPc film formation. These were possible reasons for durability improvement. The Au layer thickness of 0.3 nm on pentacene was optimal to achieve the condition with both less attenuation of visible light necessary for electric power generation and larger absorption of UV light causing degradation. Annealing treatment before CuPc evaporation brought both preferable initial performance and durability for OSCs with a combinational structure of the ITO/pentacene layer/Au layer. An appropriate region of annealing temperature had, however, a small window around 100°C.

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.

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.