Solution-processed Oxide Research Articles

Selective Isolation of Surface Grain Boundaries by Oxide Dielectrics Improves Cd(Se,Te) Device Performance.

Cd(Se,Te) photovoltaics (PV) are the most widely deployed thin-film solar technology globally, yet continued efficiency improvements are stymied by challenges at the device hole contacts. The inclusion of solution-processed oxide layers such as AlGaOx in the contact stack has yielded improved device open-circuit voltages (VOC) and fill factors (FF). However, contradictory mechanisms by which these layers improve the device properties have been proposed by the research community. We demonstrate in this work that an underappreciated property of such spin-coated layers is the preferential deposition at grain boundaries, a process that isolates the grain boundaries during contact metallization. The effects of grain-boundary isolation are probed by varying the coverage of solution-processed AlGaOx "barrier" layers on the Cd(Se,Te) surface, quantified by scanning Auger microscopy. Examining coverage-dependent VOC and FF, it was observed that isolating the grain boundaries during metallization is sufficient to prevent damage to the absorber that occurs in devices lacking a barrier layer, while additional coverage contributes to the increased series resistance. Such an effect is agnostic to the material used as a barrier layer, as long as the material does not itself damage the absorber. Spin-coated SiOx was used in place of AlGaOx for an equally beneficial effect. This grain-boundary isolation phenomenon is also observed during Mo deposition and in absorbers that have been contacted with a nitrogen-doped ZnTe layer. The mechanisms by which metallization may degrade the absorber are discussed, as are contact design strategies leveraging barrier layers, which may lead to improved device efficiencies.

Interfacial Electronic Charge Trapping and Photonic Carrier Excitation Coupling in Solution-Processed Zinc-Tin Oxide Thin-Film Transistors Applied for Logic Gate Design and Quantized Neural Network.

Components needed in Artificial Intelligence with a higher information capacity are critically needed and have garnered significant attention at the forefront of information technology. This study utilizes solution-processed zinc-tin oxide (ZTO) thin-film phototransistors and modulates the values of VG, which allows for the regulation of electron trapping/detrapping at the ZTO/SiO2 interface. By coupling the excited photonic carrier and electronic trapping, logic gates such as "AND," "OR," "NAND," and "NOR" can be achieved. With the exponential growth in data generation, efficient processing and storage solutions are imperative. However, extensive data transfer between computing units and storage limits the level of artificial neural networks (ANNs). Consequently, quantized neural networks (QNNs) have gained interest for their reduced computational resource requirements and lower consumption. In this context, we introduce an optimized ternary logic circuit based on ZTO devices. By utilizing optical modulation to adjust the turn-on voltage of the single device, we demonstrate the achievement of ternary current states, thereby providing three distinct discrete states. This configuration can be extended to QNN computing, demonstrating multilevel quantized current values for in-memory computation. We achieved a handwriting digit recognition rate of 91.6%, thereby demonstrating reliable QNN hardware performance. This robust QNN performance indicates that the metal oxide phototransistor shows significant potential for future ternary computing systems.

Pseudologic Optical Circuit Method for Advanced Color Sensing in IGZO Phototransistor Arrays with Chlorophyll Absorption Layers.

Recently, the elimination of color filters has become a key focus in photodetector research because of the potential to create more compact and cost-effective sensor systems. In this study, a novel concept of a filter-free color-discrimination photosensor using an indium gallium zinc oxide (IGZO, In/Ga/Zn = 3.1:2.6:1.0)-based phototransistor with an integrated chlorophyll absorption layer (CAL) and a solution-processed oxide absorption layer (SAL) was developed. Chlorophyll, known for its role in photosynthesis as a natural light absorber, offers distinct characteristics compared to conventional photodetectors (i.e., SAL/IGZO), whereby the photoresponsivity decreases with increasing wavelength. Using the ability of chlorophyll to absorb blue and red light, the proposed CAL/IGZO phototransistor exhibited a higher photoresponsivity to red light than to green light. The device achieved a photoresponsivity of 1570 A/W for red light and 681 A/W for green light, with a photosensitivity of 8.35 × 105 and 8.96 × 104 and a detectivity of 8.47 × 1011 and 6.80 × 1010 Jones, respectively, under an illumination intensity of 1 mW/mm2. Furthermore, by integrating the proposed CAL/IGZO phototransistor with a SAL/IGZO phototransistor, which exhibited a different order of photoresponse across RGB wavelengths, an innovative color-discrimination pixel pseudologic circuit was successfully developed. The capability of this circuit to distinguish colors across various light intensities was validated through experimental data and SPICE simulations, with the output voltage ranges confirmed as -2.61 to -3.51 V for red, 1.56 to 2.69 V for green, and -0.22 to -0.68 V for blue over light intensities from 0.1 to 3 mW/mm2. This innovative approach allows effective color detection without conventional color filters, providing an advanced solution for photodetection technologies.

Exploring the Effect of Dy Doping on the Performance of Solution-Processed Indium Oxide Thin Films and Thin-Film Transistors

Exploring the Effect of Dy Doping on the Performance of Solution-Processed Indium Oxide Thin Films and Thin-Film Transistors

Application of Solution-Processed High-Entropy Metal Oxide Dielectric Layers with High Dielectric Constant and Wide Bandgap in Thin-Film Transistors.

High-k metal oxides are gradually replacing the traditional SiO2 dielectric layer in the new generation of electronic devices. In this paper, we report the production of five-element high entropy metal oxides (HEMOs) dielectric films by solution method and analyzed the role of each metal oxide in the system by characterizing the film properties. On this basis, we found optimal combination of (AlGaTiYZr)Ox with the best dielectric properties, exhibiting a low leakage current of 1.2 × 10-8 A/cm2 @1 MV/cm and a high dielectric constant, while the film's visible transmittance is more than 90%. Based on the results of factor analysis, we increased the dielectric constant up to 52.74 by increasing the proportion of TiO2 in the HEMOs and maintained a large optical bandgap (>5 eV). We prepared thin film transistors (TFTs) based on an (AlGaTiYZr)Ox dielectric layer and an InGaZnOx (IGZO) active layer, and the devices exhibit a mobility of 18.2 cm2/Vs, a threshold voltage (Vth) of -0.203 V, and an subthreshold swing (SS) of 0.288 V/dec, along with a minimal hysteresis, which suggests a good prospect of applying HEMOs to TFTs. It can be seen that the HEMOs dielectric films prepared based on the solution method can combine the advantages of various high-k dielectrics to obtain better film properties. Moreover, HEMOs dielectric films have the advantages of simple processing, low-temperature preparation, and low cost, which are expected to be widely used as dielectric layers in new flexible, transparent, and high-performance electronic devices in the future.

The Influence of Nickel Doping on the Metal-Oxide in Solution-Processed Transistors Based on Indium Zinc Oxide

Solution-processing of nickel zinc oxide (IZO) thin-film transistors (TFTs) is gaining traction as a cornerstone of future display technology, promising cost-effective production. However, achieving stability in the off-current state of IZO without using Ga, a less eco-friendly dopant, remains a challenge. This study proposes a solution-based doping method for IZO semiconductors employing a Ni carrier suppressor and examines the impact of Ni on transistor operation. By leveraging the similar size of Ni2+ to Zn2+, an optimal Ni concentration selectively substitutes Zn sites, leading to a reduction in hydroxide groups bonded to Zn and enhancing the bonding strength of Ni with O. Conversely, excessive Ni addition impedes the formation of a smooth thin film. Ni-doped IZO TFT devices with optimized Ni concentrations exhibit superior performance, characterized by significantly lower off-state currents while maintaining high on-state currents compared to conventional IZO TFTs. This approach expands the repertoire of solution-processed metal oxide semiconductors, offering a sustainable alternative for carrier suppression and facilitating the cost-effective and straightforward fabrication of TFTs.

Engineered Catalyst Patterns on Hematite Photoanodes for Improved Photoelectrochemical Water Oxidation Efficiency

The heavy dependence on fossil fuels is a major contributor to global warming, creating an urgent need for a swift transition to renewable energy sources like solar irradiation. Photoelectrochemical (PEC) cells present a promising method for converting solar energy into chemical fuels. However, the current efficiency of PECs is inadequate for large-scale commercialization. One key obstacle to improving PEC efficiency lies in the complex and inefficient processes, from photon absorption by semiconductors to the selective transfer of photogenerated charges to redox species in the electrolyte. This study proposes a novel approach to boost PEC performance by utilizing three-dimensionally patterned catalysts on solution-processed metal oxide semiconductors, focusing on optimizing the crucial electrolyte | catalyst | semiconductor interface. By applying patterned cobalt-based catalysts onto hematite (α-Fe2O3) nanorods through a photomask-free, light-guided electrodeposition technique, we achieve direct control over the catalyst's location and distribution on the photoelectrode without relying on photolithography. The resulting electrolyte | patterned catalyst | α−Fe2O3 interface not only ensures sufficient light absorption in the front-illumination setup but also enhances the transport and transfer of photogenerated holes across the interface, reducing carrier recombination and minimizing parasitic light absorption and scattering by the catalytic layers. We confirm that electrodeposition on hematite does not affect the semiconductor's energy profile, including key parameters such as flat-band potential, carrier density, and band structure. The improved performance in PEC water oxidation is primarily due to the increased light absorption achieved by our patterned catalyst | α−Fe2O3 photoelectrode, as demonstrated by UV-Vis spectroscopy absorbance data.

Solution-Processable Metal-Oxide Thin-Film Transistors with Radiation Resistance

The impact of 5 MeV high-energy proton irradiation on solution-processed metal-oxide thin-film transistors (TFTs) has been studied. TFTs based on zinc oxide (ZnO) and indium gallium zinc oxide (a-IGZO) showed a substantial negative shift in threshold voltage values (ΔVth ≤ −30 V) or transitioned to a conductor state as the proton radiation dose increased. This effect is attributed to the formation of proton irradiation-induced oxygen vacancies in the metal-oxide semiconductor layer. Conversely, zinc tin oxide (ZTO) devices with an optimized composition demonstrated good stability due to the strong oxygen binding characteristics of tin atoms. Additionally, back-channel passivation of oxide semiconductor TFTs with an n-type organic semiconductor layer significantly improved device stability. Our research indicates that solution-processed metal oxide semiconductors hold significant promise as radiation-resistant large-area electronic devices for nuclear and aerospace applications.

Rapid activation of a solution-processed aluminum oxide gate dielectric through intense pulsed light irradiation.

In this study, we report rapid activation of a solution-processed aluminum oxide gate dielectric film to reduce its processing time under ambient atmosphere. Aluminum precursor films were exposed to a high energy light-pulse and completely converted into dielectric films within 30 seconds (450 pulses). The aluminum oxide gate dielectric film irradiated using intense pulsed light with 450 pulses exhibits a smooth surface and a leakage current density of less than 10-8 A cm-2 at 2 MV cm-1. Moreover, dielectric constants of the aluminum oxide layer were calculated to be approximately 7. Finally, we fabricated a solution-processed indium gallium zinc oxide thin-film transistor with AlO x using intense pulsed light irradiation, exhibiting a field-effect mobility of 2.99 cm2 V-1 s-1, threshold voltage of 0.73 V, subthreshold swing of 180 mV per decade and I on/I off ratio of 3.9 × 106.

Graphene Oxide-Doped Indium Oxide Buffer Film Sandwiched between Titanium Oxide Layers for the Development of Photosensitive Resistive Memory Devices.

Over the past decade, metal oxide semiconductors have attracted considerable attention because of their transparency, high intrinsic charge carrier mobility, and charge carrier density. Metal oxide semiconductors also provide a promising route to develop resistive memory devices because of the tunability of their conductivity via the removal of oxygen ions, forming oxygen vacancies that can act as electron donors. Here, this paper reports the fabrication of a resistive random-access memory (ReRAM) device with TiO2 and TiO2-x layers and introduces a solution-processed In2O3-graphene oxide (GO) buffer layer from a water-based precursor solution to tune the switching characteristics. The devices were compared with a ReRAM device with no buffer layer, and the device composition was optimized by tuning the GO concentration in the layers. The devices showed hysteresis under cyclically scanned bias between positive and negative voltages with clear switching between the low resistance state (LRS) and the high resistance state (HRS). The optimized device also showed a more than 3 orders of magnitude difference in resistance between the LRS and HRS and a stable current retention. The devices also showed photoresponsive behaviors. In the LRS, the current increased significantly under illumination, while in the HRS, the current deteriorated slowly when constantly illuminated. These results highlight the dual role of the GO flakes in the buffer layer by increasing the resistance in the HRS and providing a photoresponsive switching capability. The ReRAM device was connected to a TFT device, and its feasibility as a memory component in a digital circuit was successfully demonstrated. These results provide a new avenue for developing metal-oxide-based ReRAM devices with GO-containing active layers.

Spectroscopic Analysis of Electrical Phenomena and Oxygen Vacancy Generation for Self-Aligned Fully Solution-Processed Oxide Thin-Film Transistors.

This work unveils critical insights through spectroscopic analysis highlighting electrical phenomena and oxygen vacancy generation in self-aligned fully solution-processed oxide thin-film transistors (TFTs). Ar inductively coupled plasma treatment was conducted to fabricate an amorphous indium zinc oxide (a-InZnO) TFT in a self-aligned process. Results showed that the Ar plasma-activated a-InZnO regions became conductive, which means that a homogeneous layer can act as both channel and electrode in the device. Several techniques were employed to probe specific aspects of the source-drain-channel interface in the fully solution-processed TFTs. X-ray absorption near-edge structure and Extended X-ray absorption fine structure were conducted to investigate the existence of oxygen vacancies, which is the main driving factor in inducing a conductive region. X-ray photoelectron spectroscopy was also used to explain the oxygen refilling mechanism. Ultraviolet Photoelectron Spectroscopy was conducted to analyze the valence band maximum and work function. Integration of these results facilitated the construction of the energy band diagram at the interface, wherein a Schottky barrier height of ∼0.37 eV was observed. By leveraging these techniques, insights into the electronic properties and performance of next-generation transistors are gained, enabling their future widespread adoption.

Enhanced electrical performance and stability of solution-processed oxide semiconductor thin-film transistors via an incorporation of deionized water oxidizer

Solution-processed amorphous oxide semiconductor thin films contain poor metal-oxygen-metal (M-O-M) networks and numerous impurities, making it difficult to manufacture high-performance semiconductor devices with excellent stability. In this study, we enhance the electrical performance and device stability of solution-processed oxide thin-film transistors (TFTs) by incorporating water molecular oxidants. In solution, a water molecule can be easily incorporated by adding deionized water (DW) to the precursor solution. The DW-incorporated precursor solutions induced the production of oxide semiconductor thin films with improved M-O-M networks and fewer defect states. Therefore, compared to conventional case, the DW-incorporated indium zinc oxide (InZnO) TFT showed improved device performances and significantly reduced changes of threshold voltage under positive gate bias stress and negative gate bias/illumination stress conditions. This approach of incorporating DW into the precursor solutions provides a promising route for fabricating high-quality amorphous semiconductor films and transistor devices.

Ultrasonic spray synthesis, photoelectric properties and photovoltaic performances of chalcogenide CaSnS3

Chalcogenide perovskites are promising lead-free, stable absorber materials for solar cells. This work reports the synthesis of orthorhombic phase pure CaSnS3 thin films by facile low temperature sulfurization of solution-processed CaSnO3 oxide precursors. Structural characterization confirms complete anion exchange to produce crystalline CaSnS3 films with vertically aligned rod-like grains. Optical studies show strong visible light absorption with direct bandgap of 1.72 eV, ideal for photovoltaics. Electrical measurements indicate p-type conductivity with hole concentration of 1.2×1017 cm-3 and mobility around 8 cm2V-1s-1 at room temperature. First-principles DFT calculations corroborate the p-type electronic structure. Prototype CaSnS3 solar cells are fabricated with TiO2 electrode, demonstrating power conversion efficiency of 2.5% under AM1.5G, open-circuit voltage of 0.55 V, short circuit current density of 11.5 mA/cm2 and fill factor of 0.62. The cells also exhibit remarkable ambient shelf stability over 6 months. The comprehensive results validate the photovoltaic potential of these earth abundant, sustainable chalcogenide perovskites synthesized via scalable low-cost solution methods. Further interface engineering can enable enhanced efficiencies.

Solution-processable copper-doped molybdenum oxide films as hole injection interfacial layer in polymer light-emitting diodes

Solution-processable copper-doped molybdenum oxide films as hole injection interfacial layer in polymer light-emitting diodes

Aqueous solution-processed In2O3 TFTs using focused plasma in gas mixtures

Solution-processed indium oxide (In2O3) thin films have been studied widely as active layers for transparent semiconducting devices because of their high charge carrier concentration, low absorbance, simple fabrication methods, and low cost. Several studies on improving the electrical characteristics of thin-film transistors (TFTs) by optimizing and fine-tuning the fabrication process and using various post-deposition treatments have been conducted to take full advantage of these semiconductor films in high-performance electronics. This study examined the effects of a focused plasma (FP) treatment on In2O3 thin films prepared using a simple solution process at 250 °C. The effects of the FP generated from N2 gas and two gas mixtures (N2-H2 and N2-H2-O2) on the electrical performance of the TFTs were analyzed. The FP treatment enhanced the electrical properties of the device, and the specific performance and stability parameters were improved by the treatment conditions. X-ray photoelectron spectroscopy showed that the FP treatment could effectively control the oxygen vacancies and carrier concentration in the solution-processed In2O3 thin films. Therefore, an FP beam is a viable method for optimizing In2O3 TFTs prepared at low temperatures for application in high-performance transparent electronic devices.

Verifying the physical role of upper-active-layer on charge transport together with bias stability in bilayer-channel oxide thin-film transistors

In this work, we report the fabrication of solution-processed bilayer-structure oxide thin-film transistors (TFTs) exhibiting superior electrical characteristics and enhanced positive/negative bias stabilities. This was achieved by tuning the carrier concentration and bandgap of the top active layer in the bilayer semiconductor. The characteristics of the top layer were modulated through aluminum (Al) doping in indium oxide semiconductors. Bilayer-channel TFTs with an optimized indium-aluminum-oxide top layer (In:Al ratio of 8:2) demonstrated effective electron transport via percolation conduction and exhibited high mobility. Furthermore, the optimized bilayer TFTs displayed small threshold voltage shifts under positive and negative bias stress, attributed to the effective formation of a quasi-two-dimensional electron gas and the suppression of oxygen vacancies. An in-depth study on engineering the carrier concentration and bandgap of the bilayer structure provides insights into material design and fabrication strategies for high-performance and stable heterostructure transistors.

Efficient gradient heating-up approach for rapid growth of high-quality amorphous ZrO2 dielectric films

High-k oxide dielectric films are indispensable for low-power-consumption oxide thin-film transistors (TFTs) applied in advanced and portable electronics. However, high-quality oxide dielectric films prepared by solution process typically require sophisticated processes and long thermal annealing time, severely limiting both the throughput manufacturing and cost-effectiveness. In this study, the influence of different heating-up methods on the surface morphology and dielectric properties was systematically investigated. Gradient heating-up method could not only substantially improve the surface morphology and quality of high-k ZrO2 films but also efficiently shorten the annealing time. The gradient heating-up process was further designed on the basis of thermal behavior of the xerogel-like precursor, which successfully realize the preparation of high-quality ZrO2 films with an annealing time of 5 min (i.e. the efficiency of thermal treatment increased by about 89%). The ZrO2 film presented excellent dielectric properties, including a low leakage current density of ∼10−8 A cm−2 (at 2 MV cm−1 ), a large areal capacitance of 169 nF cm−2 and a high dielectric constant of 20.41 (1 MHz). Furthermore, InSnZnO TFT based on the ZrO2 gate dielectrics shows an acceptable device performances, such as a high carrier mobility of 2.82 cm2 V−1 s, a high on/off current ratio of ∼105 and a low subthreshold swing of 0.19 V decade −1 at a low operation voltage of 5 V. This work provide a highly promising approach to fabricate high-quality solution-processed high-k oxide dielectric films employed for large-scale and low-power-consumption electronics.

A Low-Temperature Solution-Processed Nickel Oxide Nanoparticles and Phosphotungstic Acid Composite as an Anode Interface Layer for Organic Solar Cells

A Low-Temperature Solution-Processed Nickel Oxide Nanoparticles and Phosphotungstic Acid Composite as an Anode Interface Layer for Organic Solar Cells

Effects of Hydrogen Plasma Treatment on the Electrical Behavior of Solution-Processed ZnO Thin Films.

In this study, the effect of atmospheric hydrogen plasma treatment on the in-plane conductivity of solution-processed zinc oxide (ZnO) in various environments is reported. The hydrogen-plasma-treated and untreated ZnO films exhibited ohmic behavior with room-temperature in-plane conductivity in a vacuum. When the untreated ZnO film was exposed to a dry oxygen environment, the conductivity rapidly decreased, and an oscillating current was observed. In certain cases, the thin film reversibly 'switched' between the high- and low-conductivity states. In contrast, the conductivity of the hydrogen-plasma-treated ZnO film remained nearly constant under different ambient conditions. We infer that hydrogen acts as a shallow donor, increasing the carrier concentration and generating oxygen vacancies by eliminating the surface contamination layer. Hence, atmospheric hydrogen plasma treatment could play a crucial role in stabilizing the conductivity of ZnO films.

Solution-Processed Low Resistivity Zinc Oxide Nanoparticle Film with Enhanced Stability Using EVOH

Solution-Processed Low Resistivity Zinc Oxide Nanoparticle Film with Enhanced Stability Using EVOH