Thermal Evaporation In High Vacuum Research Articles

Fabrication, electrical performance analysis and photovoltaic characterization of β-H2Pc/p-Si heterojunction for solar cell device applications

The aim of this study was to explore the potential of nanocrystalline β-metal-free phthalocyanine (β-H2Pc) in optoelectronics, particularly for the creation of a β-H2Pc/p-Si heterojunction. With a focus on photovoltaic performance, the present work aimed to assess its thermal stability, crystalline structure, optical characteristics, electrical behavior, and applicability in optoelectronic applications. We successfully fabricated a β-H2Pc/p-Si heterojunction at room temperature using a conventional high-vacuum thermal evaporation method, offering a practical approach for integrating these materials into electronic devices. Thermal gravimetric Assessment (TGA) confirmed β-H2Pc’s remarkable thermal stability up to 470 °C, which holds significant promise for high-temperature applications. Transmission Electron Microscopy (TEM) revealed the nanocrystalline nature of the deposited β-H2Pc, which is crucial for the structural integrity of advanced electronic devices. The absorption coefficient spectrum exhibited distinct absorption bands attributed to π–π* excitations, with electronic transitions identified and characterized by a 1.51 eV onset band gap and a 2.74 eV fundamental optical energy gap, highlighting its potential in optoelectronic applications. The current–voltage characteristics of the β-H2Pc/p-Si heterojunction displayed a diode-like behavior at various temperatures, with excellent rectifying properties. Photovoltaic behavior under illumination showed a power conversion efficiency of 1.1%, emphasizing its promise for renewable energy applications and future optoelectronic devices.

Novel Frequency Dependent OFET Attenuator Using ClInPc with Al2O3 Embedded Nanoparticles in Nylon 11 for Flexible Electronics

The Organic field-effect transistors (OFETs) have been largely investigated due to their low-cost manufacturing, flexibility, and lightweight, as well as their optical and electrical characteristics. That allow its application in sensors, amplifiers, attenuators signal filtering, and high-frequency response devices, like biosensing, wearable electronics, optoelectronics, telecommunications, and other potential applications. Throughout this investigation, a ClInPc flexible OFET with Al2O3 embedded particles in nylon 11, was manufactured and characterized to evaluate the optoelectronic and morphological properties. For the manufacturing, a high-vacuum thermal evaporation deposition technique was used, and UV-vis spectroscopy analysis and scanning electron microscopy were conducted to evaluate the optoelectronic and morphological properties. Also, a study regarding the electrical characteristics for different time-dependent wavefunction input signals, changing the input voltage and frequency, has been conducted. The latter was driven to determine the time-response characteristics, gains, phase shift and to determine whether the device function as an attenuator or an amplifier with the selected configuration. The device has been modelled to obtain the OFET operation parameters. A resulting capacitance of 567 pF was calculated. Uniform and continuous films where obtained, which guarantees an efficient charge transport. For all signals the output voltage is lower than that of the input voltage. Also, for the higher frequency the output voltage is decreased compared to lower frequencies. Gains decreasing variation of up to 0.05 indicate the operating application as an attenuator. Phase variation of up to 100 °, resulted while varying the input frequency. The model resulted on a gate capacitance value between 500 and 1180 pF, and gate-drain capacitance value between 50 and 500 pF. All of this could give evidence that state of the art ClInPc flexible OFET device with Al2O3 embedded nanoparticles in nylon 11 could be used toward current high-performance frequency-dependent flexible applications.

Influence of the Coordinated Ligand on the Optical and Electrical Properties in Titanium Phthalocyanine-Based Active Films for Photovoltaics.

Tetravalent titanyl phthalocyanine (TiOPc) and titanium phthalocyanine dichloride (TiCl2Pc) films were deposited via the high-vacuum thermal evaporation technique and subsequently structurally and morphologically characterized, to be later evaluated in terms of their optoelectronic behavior. The IR and UV-vis spectroscopy of the films displayed α- and β-phase signals in TiOPc and TiCl2Pc. Additionally, the UV-vis spectra displayed the B and Q bands in the near-UV region of 270-390 nm and in the visible region between 600 and 880 nm, respectively. The films presented the onset gap (~1.30 eV) and the optical gap (~2.85 eV). Photoluminescence emission bands at 400-600 nm and 800-950 nm are present for the films. One-layer ITO/TiCl2Pc or TiOPc/Ag and two-layer ITO/PEDOT:PSS/TiCl2Pc or TiOPc/Ag planar heterojunction devices with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) deposited by the spin-coating technique were constructed. In these devices, an electrical activation energy between 0.18 and 0.21 eV and a refractive index between 1.14 and 1.44 were obtained. The devices presented a change in the J-V curves for the illuminated and darkness conditions, as much as 1.5 × 102 A/cm2, related to the device architecture and phthalocyanine ligand. The latter indicates that the films should be used for optoelectronic applications.

Deposition and Characterization of Heterostructures Based on Doped Ferrocene for Film-Device Applications

Novel heterostructures based on ferrocenium hexafluorophosphate (FcPF6), 2,6-dihydroxyanthraquinone (DHAQ) or 2,6-diaminoanthraquinone (DAAQ), zinc phthalocyanine (ZnPc) and nylon 11 were deposited by the high-vacuum thermal evaporation (HVTE) technique. Morphological and mechanical characterizations of these organic heterostructures FcPF6:DHAQ/nylon(ZnPc) and FcPF6:DAAQ/nylon(ZnPc) were carried out. Subsequently, corresponding optical parameters were calculated. The heterostructure with FcPF6:DHAQ presented the lowest optical band gap and fundamental band gap at 1.55 eV and 2.45 eV, respectively. The nylon(ZnPc) layer favors the optical behavior and places these heterostructures within organic low-bandgap semiconductor range. Additionally, devices were fabricated, and their electrical behavior was evaluated. The ITO/FcPF6:DHAQ/nylon(ZnPc)/Ag device exhibits ohmic behavior, and the ITO/FcPF6:DAAQ/nylon(ZnPc)/Ag device exhibits ohmic behavior at low voltages, but at V ≥ 5 V, its behavior changes to Space Charge Limited Current (SCLC). This device carries a maximum current of 0.02 A, three orders of magnitude higher than the current carried by the device with the DHAQ. The SCLC conduction mechanism showed a hole mobility of 9.27 × 10−8 (cm2)/Vs, the concentration of thermally excited holes of 3.01 × 1023 m−3, and trap concentration of 3.93 × 1021 m−3. FcPF6:DHAQ/nylon(ZnPc) and FcPF6:DAAQ/nylon(ZnPc) are potential candidates for organic devices as an emitter layer and active layer, respectively.

Optimized thermoelectric performance in thin (Bi2Se3)1−x(Bi2Te3)x alloyed films

Herein, thin films of (Bi2Se3)1−x(Bi2Te3)x were synthesized by thermal evaporation in high vacuum using highly crystalline bulk samples of Bi2Se3 alloyed with Bi2Te3. Preparation and characterization together with probing the thermoelectric properties of thin (Bi2Se3)1−x(Bi2Te3)x films are discussed in this article. Crystal structure, surface morphology, roughness and lattice features of the deposited films were probed via XRD, SEM and HRTEM techniques, which confirmed the perfect crystallinity and the nano-scalability of the prepared thin films. Thermoelectric measurements were carried out for the as-deposited films within a temperature range of 300–473 K. Seebeck coefficient of the studied samples is about two times larger than that of the previously reported bulk samples. The highest power factor was recorded at 131 μW/m K2 at 473 K. The high value of the power factor shows that the materials under the study are promising for applications such as resource recovery of waste and also as nanomaterials for environmental applications. Very low electronic thermal conductivity was obtained due to the small electrical conductivity and due to the scattering of carriers by the tiny grains constituting the prepared films.

Innovative Implementation of an Alternative Tetrathiafulvene Derivative for Flexible Indium Phthalocyanine Chloride-Based Solar Cells.

Herein, we present the photovoltaic properties of an indium phthalocyanine chloride (InClPc)-based flexible planar heterojunction device, introducing the tetrathiafulvene derivative 4,4′-Dimethyl-5,5′-diphenyltetrathiafulvalene (DMDP-TTF) as the electron donor layer. UV-vis spectroscopy is widely used to characterize the electronic behavior of the InClPc/DMDP-TTF active layer. The interactions between the DMDP-TTF and phthalocyanine are predominantly intermolecular and the result of the aggregation of InClPc. Tauc bands were obtained at 1.41 and 2.8 eV; these energy peaks can result in a charge transfer ascribed to the transition from the DMDP-TTF to π-orbitals that are associated with the phthalocyanine ring or even with the same indium metal center. Conductive carbon (CC) was used for the cathode. Finally, an indium tin oxide (ITO)/InClPc/DMDP-TTF/CC device was fabricated by high-vacuum thermal evaporation onto a flexible substrate and the photovoltaic properties were evaluated. A diode type I-V curve behavior was observed with a photovoltaic response under illumination. A generated photocurrent of 2.25 × 10−2 A/cm2 was measured. A conductivity reduction with the incident photon energy from 1.61 × 10−7 S/cm to 1.43 × 10−7 S/cm is observed. The diode resistance presents two different behaviors with the applied voltage. A VTFL of 5.39 V, trap concentration of 7.74 × 1016 cm−3, and carrier mobility values of ~10−6 cm2/V s were calculated, showing improved characteristics via the innovative implementation of an alternative TTF-derivative, indicating that the DMDP-TTF has a strong interaction at the junction where free available states are increased, thus inducing higher mobilities due to the large number of π-orbitals, which indicates the feasibility of its use in solar cells technology.

Magnetic τ-MnAlC thin film fabrication by high-vacuum thermal evaporation

Polycrystalline τ-MnAlC thin films were produced by thermal evaporation technique in one-step deposition and using as target materials a homogeneous τ-MnAlC(100%) and a heterogeneous ε-MnAlC(73.9%)/τ-MnAlC(22.0%)/Al6Mn(4.1%) alloy, both keeping the same atomic percent for each constituent element. X-ray diffraction patterns evidence all films present a high concentration of the desired τ-phase. A microscopy analysis shows the thermal evaporation induces an island-type deposition of nanocrystalline grains with an average size of 9 nm. A hysteresis loop shows the highest concentration τ-MnAlC film exhibits a superparamagnetic-like behavior, an extremely important nanomagnetic state for the development of actuators and magnetic field sensor.

Enhanced third order optical nonlinearity in ultrathin amorphous film of tetraphenyl-porphyrin in picosecond regime

The third order optical nonlinearity of ultrathin 5, 10, 15, 20-Tetraphenyl-21H, 23H-porphine (TPP) films fabricated on an ultrasonically cleaned glass-substrate, by high vacuum thermal evaporation method is investigated. The powder X-ray diffraction (XRD) pattern demonstrates the amorphous nature of the fabricated thin film. The atomic force microscopy (AFM) and the field emission scanning electron microscope (FESEM) images show that the surface morphology of thin film composes of randomly oriented particles with the mean surface roughness of 17.73 nm. The structure of TPP thin film portrays a characteristic UV–Visible spectrum due to π-π* transitions in the porphyrin molecule. The photoluminescence spectroscopic study reveals that the TPP exhibits excellent fluorescence emission from S1 singlet excited state. The third order optical nonlinearity is studied using single beam Z-scan technique at 532 nm with picosecond pulsed (Δτ = 30 ps) laser. The TPP thin film exhibits saturation absorption property, with the effective two-photon absorption coefficient (βeff) of the order of 10−6 m/W. The observed nonlinear saturation absorption behavior is largely influenced by one-photon absorption due to the filling effect of the surface states and the localized defect states in the thin film. The closed aperture Z-scan study highlights the self-defocusing nature of the TPP thin film with negative nonlinear refractive index (n2) of the order of 10−13 m2/W. The enhanced n2 value is attributed to the highly polarizable structure of free base TPP molecule and modified electronic band structure due to the strong intermolecular interactions observed in the condensed state.

Electrical and Photovoltaic Responses of an Au/Coumarin 337/n-Si/Sb-Au Hybrid Organic–Inorganic Solar Cell

Thin films of coumarin 337 (C-337) dye were fabricated on n-type silicon (111) wafer using a high-vacuum thermal evaporation technique. Investigation of their structure using x-ray diffraction analysis and scanning electron microscopy revealed that the pristine C-337 films had sphere-shaped nanostructure. The absorbance, transmittance, and reflectance of the C-337 films were measured spectrophotometrically. Tauc’s method revealed an indirect allowed-type optical transition for these films with an optical band gap of 1.59 eV assisted by phonons of 52 meV. Hybrid organic–inorganic heterojunction solar cells based on C-337 were deposited on n-type single-crystal silicon wafer. Many aspects of the electrical parameters of the Au/C-337/n-Si/Sb-Au heterojunction solar cells were studied under dark condition based on their capacitance–voltage, conductance–voltage, and current–voltage characteristics at different frequencies (100 kHz to 1 MHz). The Nyquist diagram of the solar cell was recorded at various frequencies. Furthermore, the illuminated current–voltage and phototransient characteristics of the cell were also measured and used to evaluate the photovoltaic performance of the device. Under illumination intensity of 90 mW/cm2, the solar cell showed good photovoltaic behavior with short-circuit current, open-circuit voltage, fill factor, and power conversion efficiency of 5.42 mA, 0.55 V, 0.59, and 4.39%, respectively. The photovoltaic and phototransient properties of the device indicate that it could be applied as both a solar cell and a linear dynamic range optoelectronic switching sensor.

Growth of Molybdenum Trioxide Nanoribbons on Oriented Ag and Au Nanostructures: A Scanning Electron Microscopy (SEM) Study.

We report the growth of molybdenum trioxide (MoO3) nanoribbons (NRs) on epitaxial Ag and oriented Au nanostructures (NSs) using an ultra-high vacuum (UHV)-molecular beam epitaxy (MBE) technique at different substrate temperatures. An approximately 2 nm silver (Ag) film has been deposited at different growth temperatures (using UHV-MBE) on cleaned Si(100), Si(110), and Si(111) substrates. For faceted Au NSs, an approximately 50 nm Au film has been deposited (using high-vacuum thermal evaporation) on a Si(100) substrate with a native oxide layer at the interface and the sample was annealed in low vacuum (≈10-2) and at high temperature (≈975°C). Scanning electron microscopy measurements were performed to determine the morphology of MoO3/Ag and MoO3/Au composite films. From energy dispersive X-ray spectroscopy elemental mapping and line scans it is found that faceted Au NSs are more favorable for the growth of MoO3 NRs than epitaxial Ag microstructures.

Synthesis and characterization of new [1]benzothieno[3,2-b]benzothiophene derivatives with alkyl-thiophene core for application in organic field-effect transistors

Abstract New benzo[b]benzo[4,5]thieno[2,3-d]thiophene derivatives were synthesized and characterized as organic semiconductors in top-contact/bottom-gate organic field-effect transistors. All these compounds are new and were fully characterized by thermogravimetric analysis, differential scanning calorimetry, UV–Vis spectroscopy and energy-resolved electrochemical impedance spectroscopy. New compounds were deposited via thermal evaporation in high vacuum to fabricated highly homogeneous thin films and investigated by atomic force microscopy (AFM) and ellipsometry. Organic field-effect transistors based on prepared compounds showed p-channel characteristics with mobilities as high as 4 cm2V-1 s−1.

Continuous roll-to-roll fabrication of organic photovoltaic cells via interconnected high-vacuum and low-pressure organic vapor phase deposition systems

We demonstrate continuous roll-to-roll (R2R) fabrication of single junction and tandem organic photovoltaic (OPV) cells on flexible plastic substrates employing a system that integrates organic deposition by high vacuum thermal evaporation (VTE) and low pressure organic vapor phase deposition (OVPD). By moving the substrate from chamber to chamber and then depositing films on stationary substrates, we achieve power conversion efficiencies of PCE = 8.6 ± 0.3% and 8.9 ± 0.2% for the single junction and tandem cells, respectively. Single junction OPVs are also fabricated on a continuously translating substrate at 0.3 cm/s, to achieve PCE = 8.5 ± 0.2%. Thin films grown on translating substrates by OVPD show <3% thickness non-uniformity and 0.66 nm root mean square surface roughness, similar to that obtained by VTE. Our results suggest that R2R film deposition comprising multiple vapor deposition technologies is a promising method for rapid speed and continuous manufacturing of high quality, small molecular weight organic electronic materials.

Effect of Sn Doping on the Crystallization Kinetics of Amorphous TlInS2 Films

The crystallization of amorphous Sn-doped TlInS2 films into three polymorphs has been studied by kinematic electron diffraction. The results demonstrate that the crystallization of 30-nm-thick amorphous films produced by thermal evaporation in high vacuum can be described by the Avrami–Kolmogorov equation: Vτ = V0[1–exp(–kτm)]. Kinematic electron diffraction patterns of the TlIn1–хSnxS2 films have been used to assess the effect of doping with Sn on the growth dimensionality and the activation energy for the crystallization of the amorphous films and the unit-cell parameters of the resultant crystalline materials. Doping extends the temperature range and effective activation energy for the crystallization of the amorphous films.

Study of the ZnSxSe1–x@Al2O3 nanostructures by X-ray diffraction and EXAFS spectroscopy

Nanocomposite systems based on ternary ZnS x Se1–x semiconductor compounds with different compositions (x = 0, 0.3, 0.5, 0.7, 1) in dielectric matrices of nanoporous anodic aluminium oxide (AAO) are synthesized by high vacuum thermal evaporation of a zinc sulfide and selenide powder mixture. The effect of the atomic concentration of solid solutions and the structural parameters of the AAO template matrix on the crystal structure of the synthesized nanocomposites and the local atomic environment of Zn and Se atoms is investigated.

Facile vapor-phase synthesis of copper nanostructures on cuprous iodide films

One-dimensional growth of copper (Cu) is observed when Cu is deposited on cuprous iodide (CuI) films at elevated temperatures by thermal evaporation in high vacuum. The morphology, crystallinity, and chemical composition were examined for the samples using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Straight single-crystalline Cu nanowires can be formed on polycrystalline CuI films at 200 °C. Anisotropic growth of Cu in one-dimension was promoted by enhancing grain growth and continuity of CuI films. At a lower temperature of 100 °C, fuzzy branching nanowires were grown on the surface of CuI films, enabling to simply fabricate a self-supporting, highly porous film of Cu. It is revealed that a CuI film serves as a functional substrate to synthesize nanostructured Cu at low temperatures. Possible growth processes are proposed to explain the observed morphology evolution of Cu with respect to synthesis conditions. The characterization of water wettability showed that the hydrophobicity was remarkably enhanced due to the formation of nanostructured Cu on the CuI films.

The formation of α-phase SnS nanostructure from a hybrid, multi-layered S/Sn/S/Sn/S thin films: Phase stability, surface morphology and optical studies

Single phase of SnS thin film was fabricated from S/Sn/S/Sn/S multilayer prepared by using atmospheric pressure and vacuum thermal evaporation methods Glancing angle high vacuum thermal evaporation technique was employed to grow Sn nanorods which facilitated the sulphur diffusion in a faster manner to prepare SnS nanoparticles. The sulphur deposition temperature, sulphur deposition time and tin deposition time were successfully tailored in the synthesis process and stabilized α-phase SnS by probing through confocal micro-Raman spectrometer. X-ray diffraction confirms the formation of SnS crystal structure at sulphur deposition temperature 200°C. The mechanism of formation of highly porous SnS phase with flower like morphology is explained from the morphological analysis of post deposition annealed film. The complete absence of any oxidation state as evident from Raman as well as EDAX analysis confirms that the proposed sulphurization method could be a suitable, simple and cheap technique for the successful sulphurization of metal films. Band gap calculation from Tauc plot showed a direct band gap value of 1.5eV for films with single phase of SnS which can be used as a p-type absorber layer in thin film solar cells. Emission studies showed the energy transitions attributed to band edge transition and due to the presence of intrinsic defects.

Fabrication and Characterization of a p-AgO/PSi/n-Si Heterojunction for Solar Cell Applications

A p-AgO/PSi/n-Si heterojunction was deposited by high vacuum thermal evaporation of silver subjected to thermal oxidation at 300 ∘C on porous silicon. Surface morphology and electrical properties of this structure have been studied. The X-ray diffraction (XRD) analysis reveals that the peaks at the (220) and (111) planes were dominated for the crystal quality of the AgO films. The band gap of the AgO films was found to be 2.2 eV and 3.2 eV . The positive sign of Hall effect confirms that the film was of p-type conductivity. The average grain size of pore was measured from the atomic force microscope (AFM) analysis and found to be around 32 nm. The responsivity photodetector after deposited AgO have revealed increasing in response.

Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation.

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. Conventionally reserved for the fabrication of metal thin films, thermal evaporation deposits bismuth into an array of vertical single crystalline nanowires over a flat thin film of vanadium held at RT, which is freshly deposited by magnetron sputtering or thermal evaporation. By controlling the temperature of the growth substrate the length and width of the nanowires can be tuned over a wide range. Responsible for this novel technique is a previously unknown nanowire growth mechanism that roots in the mild porosity of the vanadium thin film. Infiltrated into the vanadium pores, the bismuth domains (~ 1 nm) carry excessive surface energy that suppresses their melting point and continuously expels them out of the vanadium matrix to form nanowires. This discovery demonstrates the feasibility of scalable vapor phase synthesis of high purity nanomaterials without using any catalysts.

Characterization of GaN/p-Si solar cell prepared by simple technique

This study involves the synthesis of nanostructure GaN films on glass and Si substrates prepared by high vacuum thermal evaporation technique. Atomic force microscopy measurements reveal that the sample was found to have a smooth surface topography. X-ray diffraction showed high-quality GaN epilayer with a hexagonal shape. The optical properties were studied using micro-photoluminescence and UV–vis spectrophotometer. Micro-photoluminescence spectra displayed intensity enhancement with blue-shifted band-edge PL peaks associated with the increasing annealing temperature. The blue shifted in absorbencies spectroscopy for GaN films further confirms such behavior. The capacitance–voltage characteristics were measured, and it is found within the range of (Vbi=0.86–1.4V). I–V characteristic of GaN/Si (p-type) heterojunction are investigated. It is found that the maximum efficiency is (4.8) at annealing temperature Ta=373K while at Ta=573K is (8.8).

Highly efficient low-bandgap polymer solar cells with solution-processed and annealing-free phosphomolybdic acid as hole-transport layers.

We demonstrate a novel solution-processed method to fabricate a stable anode buffer layer without any annealing process. As we know, buffer layers in polymer solar cells (PSCs) are always prepared by the traditional high-vacuum thermal evaporation or annealing-treated spin-coating methods, but the fabricating processes are complicated and time-consuming. Here, a solution method without any annealing to fabricate phosphomolybdic acid (PMA) as anode buffers is presented, which brings an obvious improvement of power conversion efficiency (PCE) from 1.75% to 6.57% by optimizing the PMA concentrations and interface pretreatment with device structure shown as ITO/TiO2/PCDTBT:PC70BM/PMA/Ag. The improvement is ascribed to the fine energy-level matching and perfect surface modification. This annealing-free method greatly simplifies the device fabrication process and supplies a wide way to achieve a large area fabrication for PSCs.