Optoelectronic Film Research Articles

A significant effect of Ce-doping on key characteristics of NiO thin films for optoelectronics facilely fabricated by spin coater

Abstract NiO has been found to have excellent physical properties which are crucial for several significant electro-optical devices. Herein, we have designed and fabricated high-quality films of NiO with various concentrations of Ce and studied their key properties. X-ray diffraction (XRD) study confirmed the cubic phase, good crystallinity and growth direction along (111) plane in the prepared samples. The crystallite size was noticed in the range of 13–30 nm. For confirming the presence of Ce doping and its homogeneity in NiO films the EDX/SEM mapping was carried out. AFM study provided the topographic information in terms of size of the grains and roughness of all films. The grown films were found to be 70–80% optically transparent in the whole testing region. Optical energy gap was found to expand from 3.60 to 3.68 eV owing to Ce-doping. The refractive index value was noticed to be in the range from 1.7 to 2.7. The n2 and χ ( 3 ) values for pure and Ce-doped NiO films varied from 2 × 10−10 to 1.4 × 10−11 and 1 × 10−12 to 1.1 × 10−11 esu, respectively. Obtained results indicated that Ce has strong influence on opto-nonlinear characteristics of NiO films and proposed their application in the opto-nonlinear devices.

In-depth study on structural, optical, photoluminescence and electrical properties of electrodeposited Cu2O thin films for optoelectronics: An effect of solution pH

Cu2O thin films were deposited using electrodeposition method at different pH values of the solution (11, 12 and 13). The prepared films were analyzed by XRD, SEM, EDAX, UV–Vis absorption and Photocurrent-voltage measurements. The XRD study revealed that there is a increase of crystallite size as 33, 42 and 52 nm for films deposited at pH of 11, 12 and 13, respectively. SEM images revealed three-face pyramid shaped grains of increased size for the increase of solution pH. Among all grown films, high absorption is found for film grown at solution pH 13. The band gap values are found to be 2.02, 1.98 and 1.92 eV, respectively for different pH values. Photoluminescence spectra displayed sharp emission peak at 618 nm which confirms the formation of Cu2O structure. The Photo response studies revealed increase of photocurrent with increase of pH value. The observed low resistivity of the films grown at solution pH 13 confirms that the film is of better quality among the other films.

Layer-by-layer MoS2:GO composite thin films for optoelectronics device applications

With reference of our previous report (Appl. Surf. Sci. 474(2019)227), the molybdenum disulphide (MoS2) thin film were prepared by the dip-coating technique at different temperatures (400 °C–450 °C) using methanolic solution of ammonium molybdate and ammonium thiocyanate that are used as bare-substrate for the deposition of graphene oxide (GO) thin films. For the deposition of graphene oxide (GO), commercially purchased GO (0.5 mg in 10 mL aqueous solution) was deposited by dip-coating technique on dip-deposited MoS2 thin film to make layer-by-layer MoS2:GO composite thin films and hence studied their electronic and electrical behaviours. The micro-structural and surface morphology were studied using Raman spectroscopy, X-ray diffraction (XRD) and field emission scanning electron microscopy, whereas optical band estimated from the optical absorption spectra. The electronic structure and their bonding properties were studied using X-ray photoelectron spectroscopy and the electrical behaviours were observed from the current-voltage (I-V) characteristic curve. The formation of different phases of MoS:GO thin films show an enhanced electronic and electrical performance due to their unique-structure and the synergetic effect of MoS2:GO nanosheets when compared to those of bare MoS2.

Graphene-Supported Thin Metal Films for Nanophotonics and Optoelectronics.

Graphene-metal hybrid nanostructures have attracted considerable attention due to their potential applications in nanophotonics and optoelectronics. The output characteristics of devices based on such nanostructures largely depend on the properties of the metals. Here, we study the optical, electrical and structural properties of continuous thin gold and copper films grown by electron beam evaporation on monolayer graphene transferred onto silicon dioxide substrates. We find that the presence of graphene has a significant effect on optical losses and electrical resistance, both for thin gold and copper films. Furthermore, the growth kinetics of gold and copper films vary greatly; in particular, we found here a significant dependence of the properties of thin copper films on the deposition rate, unlike gold films. Our work provides new data on the optical properties of gold and copper, which should be considered in modeling and designing devices with graphene-metal nanolayers.

Simple two-step for optoelectronic films

Simple two-step for optoelectronic films

Research on Prediction Method of Performance Degradation of Flexible Optoelectronic Film Material Processing Equipment Based on Adaptive Fuzzy Clustering

Flexible photoelectric film is an anisotropic material. The slight change of equipment performance during processing is prone to cause deformation of the material. Therefore, it is important to predict the degradation of processing equipment performance. Since the performance degradation of flexible photoelectric film material Roll-to-Roll (R2R) processing equipment is a nonlinear process, this paper introduces an adaptive fuzzy clustering method to construct a fuzzy membership function model for calculating the performance degradation index of R2R processing equipment and studies the parameter solving method such as the AFCM division of the roller vibration data, the category center value of the fuzzy membership function, and the input data division area width. Finally, the performance degradation index calculation algorithm is designed. The roller shaft accelerated life test was carried out using self-made equipment. The test data were 1000 sets. The results showed that the root mean square eigenvalues and the kurtosis eigenvalues of the roller vibration data are sensitive to the performance degradation. The equipment performance curve described by the first and second types of performance degradation indicators was very stable in the early stage. After the 800th group, the curve continued to decrease, and the change was more severe, indicating that the performance degradation of the equipment is more serious. In the 980th group, the longer-lasting roller shaft was damaged, and the performance index value was about zero, which proved the correctness of the performance degradation prediction method proposed in this paper in calculating the performance degradation value of the equipment.

Reconstruction of Solar Fuel Ultrathin Films via Periodically Microbending for Efficient Photoelectrochemical Water Splitting

Tackling the conflict between the optical and electronic properties of the ultrathin optoelectronic films is of critical importance for the development of highly efficient photoenergy conversion devices. We show in this report a proof of concept for designing an ultrathin photoelectrode film that compensates intrinsic low absorption coefficients and limited charge-carrier transport properties. To enhance light absorption under these conditions a light trapping structure using coupled optical properties was designed on the basis of an array of hollow half spheres generated by periodically microbending the deposited thin film, yielding well-defined two-dimensional ordered microspaces. Exemplified by α-Fe2O3, this film structure is able to generate an approximately 4.5-fold increase in photocurrent at a bias of 1.23 V versus RHE under simulated solar radiation conditions compared to that of a flat film with the same thickness. Both the experimental results and the theoretical simulations prove that modulatin...

Photonic band engineering in absorbing media for spectrally selective optoelectronic films.

Spectrally selective materials are of great interest for optoelectronic devices in which wavelength-selectivity of the photoactive material is necessary for applications such as multi-junction solar cells, narrow-band photodetectors, transparent photovoltaics, and tailored emission sources. Achieving controlled transparency or opacity within multiple wavelength bands in the absorption, reflection, and transmission spectra are difficult to achieve in traditional semiconductors that typically absorb at all energies above their electronic band gap and is generally realized by the use of external bandpass filters. Here, we propose an alternate method for achieving spectral selectivity in optoelectronic thin films: the use of photonic band engineering within the absorbing region of a semiconductor in which resonant photonic bands are strongly coupled to the external reflectivity and transmission spectra. As a first step, we use optical simulations to systematically study the effect of material absorption on the properties of the photonic bands in a photonic crystal slab structure. We find that adding a weak loss to the materials model does not appreciably change the frequencies of the photonic bands but does reduce the quality factor of the associated photonic modes. Critically, the radiating photonic bands induce strong Fano resonance features in the transmission and reflection spectra, even in the presence of material absorption, due to coupling between the bands and external electromagnetic plane waves. These resonances can be tuned by adjusting the photonic crystal structural properties to induce spectral selectivity in the absorbing region of semiconductors. Lastly, we demonstrate this tuning method experimentally by fabricating a proof-of-principle photonic structure consisting of a self-assembled polystyrene bead monolayer infiltrated with PbS CQDs that displays both near-infrared absorption enhancement and visible transparency enhancement over a homogeneous control film, qualitatively matching predictions and showing promise for optoelectronic applications.

Development towards simple fabrication steps for flexible optoelectronic films

Recent developments in flexible circuits and optoelectronic materials have the potential to provide innovative solutions for wearable sensing. The presented work explores how materials from these developments can reduce the complexity of developing flexible optoelectronics. The work uses simplified fabrication methods to develop a large area thin film optoelectronic device using conjugated polymers and Quantum Dots, with the goal of providing evidence that such devices can be developed outside of a clean room facility. Electroluminescence testing using a power source and an imaging spectrometer show that both conductive polymers and Quantum Dots in the functional layer contribute to light emission. High voltages needed for light emission are likely a result of the observed uneven thicknesses in the active layer, which should be the main focus for improvement in continued work. To study flexibility, the effects of cyclic bending using an Instron machine is observed. Visual analysis identifies four main flaw features that can occur from the fabrication process, and that cyclic bending causes cracking only at these flaw features. This work serves as evidence that use of clean room facilities are not necessary to provide significant contributions towards flexible optoelectronic materials development.

Studies on NiO-PVA Composite Films for Opto-Electronics and Optical Limiters

We report optical, excited-state lifetime, and nonlinear optical (NLO) properties of nickel oxide (NiO)/poly vinylalcohol (PVA) polymer free-standing films for opto-electronics and optical limiting applications. Optical absorption studies of NiO-loaded PVA films show that the exciton peaks are centered at 330 nm. Fluorescence studies reveal that the emission is due to exciton recombination and defects in NiO. Time-resolved fluorescence studies show that the recombination in PVA happens through NiO, where NiO has a faster decay time than the pure PVA. NLO measurements carried out using a 532 nm, 10-ns Nd: YAG laser, show that for a given energy, NiO/PVA shows good optical limiting, and the obtained NLO behavior is due to effective two-photon absorption.

Effects of excimer laser annealing energy on the properties of thermally evaporated tin antimony sulfide thin films and TEM characterization of the powder

Tin antimony sulfide (TAS) is one of the most promising compounds for the next generation of optoelectronic and thin film photovoltaic devices. TAS material was synthesized by a solid-state reaction using earth-abundant tin, antimony and sulfur elements. The structural properties of the TAS powder were investigated by transmission electron microscopy (TEM). X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and selected electron diffraction (SAED) were employed to establish the crystalline nature of the powder. The TEM observations demonstrated that the powder was polycrystalline in nature with rod-shaped structure. The effects of excimer laser annealing (ELA) at different pulse energies on the structural, morphological and optical properties of thermally evaporated TAS films were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy measurements showed that the films annealed by an excimer laser of 248 nm were amorphous for weak energy densities whereas the sample irradiated with 111 mJ/cm− 2 was polycrystalline with a preferential $${\text{(}}\overline {{\text{2}}} {\text{1}}\overline {{\text{3}}} {\text{)}}$$ orientation. The ELA effects on the optical properties were also studied in the wavelength range 300–1800 nm by using UV–Vis–NIR spectroscopy. The absorption coefficient of all samples in the fundamental absorption region is higher than 104 cm−1. We also found that the optical band gap decreases from 2.04 to 1.84 eV after irradiating the thin films under different laser energy densities.

Spray-Coated CsPbBr3 Quantum Dot Films for Perovskite Photodiodes.

Large-area film deposition and high material utilization ratio are the crucial factors for large-scale application of perovskite optoelectronics. Recently, all-inorganic halide perovskite CsPbBr3 has attracted great attention because of its high phase stability, thermal stability, and photostability. However, most reported perovskite devices were fabricated by spin-coating, suffering from a low material utilization ratio of 1% and a small coverage area. Here, we developed a spray-coating technique to fabricate a CsPbBr3 quantum dot (QD) film photodiode which had a high material utilization ratio of 32% and a deposition rate of 9 nm/s. The film growth process was studied, and substrate temperature and spray time were two key factors for the deposition of uniform and crack-free QD films. The spray-coated photodiode was demonstrated to be more suitable for working in the photodetector mode because a low dark current density of 4 × 10-4 mA cm-2 resulting from an extremely low recombination current contributed to a high detectivity of 1 × 1014 Jones. A high responsivity of 3 A W-1 was obtained at -0.7 V under 365 nm illumination, resulting from a low charge-transfer resistance and a high charge recombination resistance. We believe that the spray deposition technique will benefit the fabrication of perovskite QD film optoelectronics on a large scale.

Optical and electrical properties of H2 plasma-treated ZnO films prepared by atomic layer deposition using supercycles

High mobility H-doped ZnO (ZnO:H) thin films are prepared on thermal oxide coated silicon wafers by a novel supercycle approach of thermal atomic layer deposition (ALD) technique. The influence of H2 plasma treatment and substrate composition on optical and electrical properties of ZnO films are studied using spectroscopic ellipsometry (SE) and direct electrical measurements. This work significantly expands the measured range of ZnO:H optical properties into the far infrared to obtain the complex dielectric function (ε = ε1 + iε2) spectra from 0.4 meV to 5.89 eV compared to what has been previously investigated by using SE. A blue shift in the optical band gap energy is observed with decreasing cycle ratio (n) or more frequent H2 plasma treatments during deposition. The amplitude of phonon absorption is increased with decreasing n. Free carrier transport characteristics are determined by applying the Drude model in modeling ε, and the result indicates lower n improves material conductivity as confirmed by direct electrical measurements. Regarding the effect of substrate composition, the samples prepared using the same n but on bare thermal oxide, a 5 nm ZnO:H film, or a 5 nm intrinsic ZnO film each have differences in ε and free carrier transport characteristics resulting from substrate composition, demonstrating an additional method of tailoring material properties. Effective carrier mass (m*) for the ZnO films are determined by combining results from Hall effect measurements with UV to THz spectra in ε. Thus, variation of n and substrate composition are demonstrated as an effective mean of controlling the resultant opto-electronic film properties.

18‐1: Invited Paper: Color Tunable, Flexible, and Efficient Light Emitting Diodes Composed of Metal Halide Perovskites

Hybrid organic‐inorganic halide perovskite materials such as methylammonium lead iodide are gaining interest in the thin film optoelectronics community due to their promising optoelectronic properties. We have established a processing paradigm to realize films with roughness on the order of 1 nanometer that consists of nanoscale crystallites, formed by incorporating a bulky organoammonium halide in addition to the stoichiometric 3D perovskite precursors. These bulky ligands passivate the 3D crystal, lead to considerably enhanced luminescence quantum yields, and increase stability. Making light emitting devices from such films result in devices with external quantum efficiency exceeding 10% and which can overcome the otherwise intrinsic brittleness of metal halide perovskite films. Finally, they allow for stabilizing mixed halide (I and Br) stoichiometries such that we can tune emission color from the green to red wavelengths.

Two nanomaterial firms raise funding

Two firms specializing in nanoscale carbon materials have raised funds to help them meet the needs of customers producing a variety of electronic devices. Nano-C, an MIT spin-off founded in 2001, raised $11.5 million from investors, including Ray Stata, cofounder of integrated circuit maker Analog Devices. Meanwhile, Nantero received $29.7 million in investments from strategic partners that include the venture arms of Dell, Cisco, and Kingston Technology. The two firms are connected: Nano-C supplies carbon nanotubes to Nantero for use in a new type of computer chip called nonvolatile random access memory. In addition to memory chips, Nano-C says, its high-purity nanotubes, fullerenes, and functionalized nanomaterials will be used in printable organic photovoltaics, extreme ultraviolet lithography photoresists, and optoelectronic films used in electronic displays. Compared to more prosaic uses of nanomaterials, such as polymer reinforcement, “electronics is definitely one of the harder application development efforts,” says Anthony Schiavo, an analyst

Metal-induced growth of crystal Si for low-cost Al:ZnO/Si heterojunction thin film photodetectors

Quality crystal silicon (Si) thin films were grown via the metal-induced growth (MIG) method, which is a low-cost and metal-silicide assisted technique. The metal catalysts of Ni, Pd and Co were first deposited onto substrates for silicide template layer formation. Then, crystal Si thin films with a thickness of ~ 5 µm were epitaxially deposited on the silicide seeds via DC magnetron sputtering. The crystallinity of the Si films was confirmed and investigated by X-ray diffraction (XRD). These Si thin films were then used to fabricate Al doped ZnO (AZO)/MIG Si heterojunction photodetectors. The device achieved a saturation photocurrent of 23.2 mA/cm2 at − 5 V. This photocurrent level is comparable with that of previous reported AZO/bulk-Si devices. Current transport mechanisms and defect distributions were also studied. By analyzing the dark current-voltage (I – V) characteristics, the space charge limited (SCL) current dominated junction behaviors with an exponential defect level distribution were determined. In the bias range of 0.25 V < V < 1.0 V, SCL current transported in the mobility regime based on I ∝ Vβ, where β > 3. For 0 < V < 0.25 V, tunneling and SCL current in ballistic regime were implied due to I ∝ V1.5. In the reverse bias, the device exhibited SCL current in saturation regime or tunneling, suggested by the unity I-V relation. The fabricated devices with the theoretical understanding of the defect and carrier transport mechanisms provided new design insights for low-cost ZnO/MIG-Si thin film optoelectronics.

Inkjet manipulated homogeneous large size perovskite grains for efficient and large-area perovskite solar cells

The performance of large-area perovskite solar cells (PSCs) is confined to the non-uniformity edge-coating and crystalline defects. Focusing on the critical requirement of large-area uniform and compact crystallized perovskite film for efficient PSCs, here, an inkjet manipulated approach is introduced for controlling the thin-film perovskite growth in a mesoporous solar cell device structure. The ink droplet wetting behavior on mesoporous substrate, the physical properties of solutions have been systematically investigated. Uniform liquid membrane was obtained via precisely controlled micro-droplets by inkjet-printing. Mesoporous substrates guarantee fast and complete coalescence of the precursor droplets, and limit random diffusion of the precursor solution. Homogeneous PbI2 film leads to a compact perovskite film with micro-scale crystalline grains, which enables PSCs high power conversion efficiencies (PCEs) of 18.64% for small area (0.04 cm2) and 17.74% for large area (2.02 cm2). The enhanced performance can be ascribed to improved uniformity of the perovskite film morphology, favorable perovskite crystallite orientation, large grain size (> 2 µm) and less grain boundaries. Inkjet manipulation provides a facile approach to fabricate large-area and high-quality films for future optoelectronics, including field effect transistors, light-emitting diodes, and sensor devices.

Deposition of Methylammonium Lead Triiodide by Resonant Infrared Matrix-Assisted Pulsed Laser Evaporation

Resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) was used to deposit the metal-halide perovskite (MHP) CH3NH3PbI3 (methylammonium lead triiodide, or MAPbI), creating phase-pure films. Given the moisture sensitivity of these crystalline, multi-component organic–inorganic hybrid materials, deposition of MAPbI by RIR-MAPLE required a departure from the use of water-based emulsions as deposition targets. Different chemistries were explored to create targets that properly dissolved MAPbI components, were stable under vacuum conditions, and enabled resonant laser energy absorption. Secondary phases and solvent contamination in the resulting films were studied through Fourier transform infrared (FTIR) absorbance and x-ray diffraction (XRD) measurements, suggesting that lingering excess methylammonium iodide (MAI) and low-vapor pressure solvents can distort the microstructure, creating crystalline and amorphous non-perovskite phases. Thermal annealing of films deposited by RIR-MAPLE allowed for excess solvent to be evaporated from films without degrading the MAPbI structure. Further, it was demonstrated that RIR-MAPLE does not require excess MAI to create stoichiometric films with optoelectronic properties, crystal structure, and film morphology comparable to films created using more established spin-coating methods for processing MHPs. This work marks the first time a MAPLE-related technique was used to deposit MHPs.

Enhanced photoluminescence of corrugated Al2O3 film assisted by colloidal CdSe quantum dots

We present the enhanced photoluminescence (PL) of a corrugated Al2O3 film enabled by colloidal CdSe quantum dots. The colloidal CdSe quantum dots are fabricated directly on a corrugated Al2O3 substrate using an electrochemical deposition (ECD) method in a microfluidic system. The photoluminescence is excited by using a 150 nm diameter ultraviolet laser spot of a scanning near-field optical microscope. Owing to the electron transfer from the conduction band of the CdSe quantum dots to that of Al2O3, the enhanced photoluminescence effect is observed, which results from the increase in the recombination rate of electrons and holes on the Al2O3 surface and the reduction in the fluorescence of the CdSe quantum dots. A periodically-fluctuating fluorescent spectrum was exhibited because of the periodical wire-like corrugated Al2O3 surface serving as an optical grating. The spectral topographic map around the fluorescence peak from the Al2O3 areas covered with CdSe quantum dots was unique and attributed to the uniform deposition of CdSe QDs on the corrugated Al2O3 surface. We believe that the microfluidic ECD system and the surface enhanced fluorescence method described in this paper have potential applications in forming uniform optoelectronic films of colloidal quantum dots with controllable QD spacing and in boosting the fluorescent efficiency of weak PL devices.

Evaporative Lithography in Open Microfluidic Channel Networks.

We demonstrate a direct capillary-driven method based on wetting and evaporation of various suspensions to fabricate regular two-dimensional wires in an open microfluidic channel through continuous deposition of micro- or nanoparticles under evaporative lithography, akin to the coffee-ring effect. The suspension is gently placed in a loading reservoir connected to the main open microchannel groove on a PDMS substrate. Hydrophilic conditions ensure rapid spreading of the suspension from the loading reservoir to fill the entire channel length. Evaporation during the spreading and after the channel is full increases the particle concentration toward the end of the channel. This evaporation-induced convective transport brings particles from the loading reservoir toward the channel end where this flow deposits a continuous multilayered particle structure. The particle deposition front propagates backward over the entire channel length. The final dry deposit of the particles is thereby much thicker than the initial volume fraction of the suspension. The deposition depth is characterized using a 3D imaging profiler, whereas the deposition topography is revealed using a scanning electron microscope. The patterning technology described here is robust and passive and hence operates without an external field. This work may well become a launching pad to construct low-cost and large-scale thin optoelectronic films with variable thicknesses and interspacing distances.