Thin Film Heterojunction Research Articles

CsPb2Br5 Plates/Quasi-2D Perovskite Heterojunction for Efficient Sky-Blue Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) have gained significant attention owing to their remarkable tunability and color stability, and substantial progress has been made with green and red PeLEDs. However, the advancement of blue PeLEDs still lags far behind their red and green counterparts. In this study, we report efficient sky-blue PeLEDs utilizing an in situ fabricated CsPb2Br5 plates/quasi-2D perovskite heterojunction using chelating molecules to modulate the crystallization process of perovskites. The wide bandgap of CsPb2Br5 facilitated the formation of a type-I band alignment at the heterojunction, allowing efficient carrier transfer from CsPb2Br5 to CsPbBr3. This heterojunction leads to a noteworthy enhancement of device efficiency. The PeLEDs exhibit a maximum brightness of 2311 cd m-2, accompanied by a maximum external quantum efficiency of 12.86% at 487 nm. Our tailored design of CsPb2Br5/perovskite heterojunction thin films offers a promising avenue for advancing PeLED performance. This work contributes valuable insights into the burgeoning field of perovskite electroluminescence, paving the way for further optimization of PeLED technologies.

Surface engineering of CuO-Cu2O heterojunction thin films for improved photoelectrochemical water splitting

The efficient production of green hydrogen poses a significant challenge that requires the development of active, low-cost, and stable catalysts. Copper oxide has emerged as a highly effective photocatalyst for water splitting, offering the advantages of being nontoxic, abundant, and inexpensive. Nonetheless, the photoelectrochemical water splitting (PEC) process can be enhanced through surface modification. In this study, we utilized single-source precursors for aerosol-assisted chemical vapor deposition (AACVD) in order to deposit thin films of copper oxide (CuO-Cu2O) heterojunctions onto a substrate composed of fluorine-doped tin oxide (FTO). The chosen precursor for this purpose was copper (II) nitrate hemi(pentahydrate). To further optimize the CuO-Cu2O films, a novel acid treatment involving the addition of varying quantities of acetic acid (AA) to the precursor solution was employed. Remarkably, this acid treatment resulted in a significant improvement in the photocurrent density of the CuO-Cu2O heterojunction. Notably, a 3 mL acid-treated CuO-Cu2O thin film exhibited an impressive photocurrent measure of −6.8 mA/cm2 at 0.0 V vs RHE in 0.5 M Na2SO4 electrolyte, compared to the performance of the untreated CuO-Cu2O thin film (−2.8 mA/cm2 at 0.0 V vs RHE). This catalyst demonstrated stability and a threefold increase in hydrogen production performance. The increase in photocurrent densities is closely linked to the influence of AA on two key factors: particle growth and structural defects, such as oxygen vacancies. This relationship has been confirmed through the examination of SEM, AFM, and PL spectra results. The findings of this study not only offer a novel approach to catalyst design but also propose a practical method for photoelectrochemical water splitting. This method holds great promise for achieving sustainable and renewable energy sources, as well as efficient green hydrogen production.

Effect of carrier gas on copper antimony sulfide thin films by spray pyrolytic approach

This study explores the ternary compound semiconductor as a potential absorber layer for third-generation solar cells. CuSbS2, a promising candidate for thin film absorber layers, is fabricated using a simple spray pyrolysis method. The research specifically investigates the influence of two different carrier gases during the fabrication process. X-ray diffraction as well as Raman studies confirm that the films exhibit a chalcostibite structure. Notably, films fabricated with nitrogen as the carrier gas demonstrate enhanced crystallinity, accompanied by reduced microstrain and dislocation density. Furthermore, these films exhibit a significantly improved absorption coefficient, reaching 105 cm-1 . Optical studies indicate that the materials possess a direct band gap of 1.50 eV and exhibit p-type conductivity. CuSbS2 thin film heterojunction solar cell exhibits a maximum efficiency of 0.49%.

Gamma radiation-induced changes in the structural and optical properties of CsPbBr3 thin films for space applications

Perovskite nanocrystals (NCs) are emerging as a next generation display technology. In this regard, exploring the structural and optical stability when subjected to radiation is crucial for expanding their application in aerospace and radiation detection technologies. In this study, we investigated the effects of gamma radiation on CsPbBr3 heterojunction thin films through a comprehensive analysis of their structural and optical characteristics. The thin films of CsPbBr3 were subjected to varying doses of gamma radiation, ranging from 100 krad to 1 Mrad, followed by thorough examination using X-ray diffraction (XRD) and optical spectroscopy techniques. Our findings unveil significant changes in the crystal structure of CsPbBr3 thin films when exposed to gamma radiation, including shifts in diffraction peak positions from cubic to monoclinic phases, broadening of peaks, and variations in peak intensities due to induced surface defects. The optical properties, such electroluminescence (EL) and photoluminescence (PL) intensity slightly drops at the moderate irradiation dose of 300 krad, while at an irradiation dose of 1 Mrad deteriorated severely. Notably, 300 krad is equivalent to the radiation dose accumulated by satellites in low-Earth orbit over 10 years. The findings in this work suggest the fabricated CsPbBr3 thin film has the potential to be used in space applications.

Viable Approach of Tuning Oxide Semiconductor Thin Films in Solution‐Processed Heterojunction Thin Films Transistors for Both Higher Performances and Stability

AbstractMetal‐oxide thin‐film transistors (TFTs) have garnered much attention because of their advantages such as high transparency, low leakage current, and low processing temperature. However, there is a need to continuously improve their mobility and bias stability for application to next‐generation advanced electronics. In this study, the thickness of bilayer semiconductors is finely controlled to enhance the charge transport characteristics and bias stability in solution‐processed heterojunction oxide TFTs. The thicknesses of the top and bottom layers in the bilayer are individually adjusted by controlling solution molarity. The introduction of a bilayer channel improved the electrical performance of oxide TFTs via effective charge transport. However, trap‐limited conduction becomes dominant in the bilayer with an excessively thick top layer, thereby leading to a significant reduction in mobility and positive bias stability. Meanwhile, although increasing the bottom layer thickness contributes to improved mobility and reliability, it causes a serious negative shift in threshold voltage (VTH). TFTs with an optimized bilayer structure show high mobility at a VTH close to 0 V and have particularly excellent positive bias stress stability. This study on bilayer channel thickness will be beneficial for developing advanced transistors with optimized bilayer or multilayer channels.

Cu2O/TiO2 core–shell nanowire heterojunction for high-performance self-powered photodetector

High-performance self-powered photodetectors (PDs) have great commercial value in optical communication, intelligent sensing and medical diagnosis. However, the limited active area of traditional thin film heterojunction seriously restricts the photoelectric performance of the detector. In this paper, the Cu2O/TiO2 core-shell nanowire (NW) heterojunction PD was synthesized for the first time by simple hydrothermal and electrochemical deposition methods, which effectively improved the response performance and response speed of the device based on its broad photoactive area and ordered carrier transport path. The PD exhibits significant diode behavior, with rectification ratios of 543 at ±2 V. The responsivity is as high as 6.8 mA W−1 at zero bias under 490 nm illumination. The short rise and decay times measured are 0.09 and 0.18 s at zero bias, respectively. Obviously, this low-cost, high-performance self-powered Cu2O/TiO2 core-shell NW heterojunction PD shows great promise in future optoelectronic device applications.

Sulfur-doped g-C3N4/GaN n-n heterojunction for high performance low-power blue-ultraviolet photodetector with ultra-high on/off ratio and detectivity

Polymeric graphitic carbon nitride (g-C3N4) shares a structural similarity to graphene, yet it possesses a distinctive electronic band structure, rendering it promising for photoelectric applications. However, g-C3N4 faces inherent limitations such as inadequate crystalline quality, limited conductivity, and a short lifespan of photogenerated charge carriers, all of which impede the photoelectric conversion efficiency. In this work, we introduce a two-step thermal vapor condensation method for depositing compact, crack-free sulfur-doped g-C3N4 thin films. The doped thin films exhibit reduced interlayer spacing, which leads to improved conductivity and charge transfer capabilities. These processes culminate in the creation of sulfur-doped g-C3N4/GaN thin film heterojunction blue-ultraviolet photodetectors with remarkable photodetection performance, including an ultrahigh on/off ratio of 7.3 × 107 and specific detectivity of 2.06 × 1014 Jones under a low bias of −0.4 V. Moreover, it is found that the n-n heterojunction undergoes a transition from photodiode to photoconduction behavior, attributed to the photoinduced electron trapping effects by sulfur-doped sites, which outcomes a notable gain with the responsivity as high as 581 mA/W. These findings underscore the vast potential of high-quality sulfur-doped g-C3N4 thin films for photoelectric applications.

In2O3/ZnO heterojunction thin film transistor for high recognition accuracy neuromorphic computing and optoelectronic artificial synapses

Solid electrolyte-gated transistors exhibit improved chemical stability and can fulfill the requirements of microelectronic packaging. Typically, metal oxide semiconductors are employed as channel materials. However, the extrinsic electron transport properties of these oxides, which are often prone to defects, pose limitations on the overall electrical performance. Achieving excellent repeatability and stability of transistors through the solution process remains a challenging task. In this study, we propose the utilization of a solution-based method to fabricate an In2O3/ZnO heterojunction structure, enabling the development of efficient multifunctional optoelectronic devices. The heterojunction’s upper and lower interfaces induce energy band bending, resulting in the accumulation of a large number of electrons and a significant enhancement in transistor mobility. To mimic synaptic plasticity responses to electrical and optical stimuli, we utilize Li+-doped high-k ZrO x thin films as a solid electrolyte in the device. Notably, the heterojunction transistor-based convolutional neural network achieves a high accuracy rate of 93% in recognizing handwritten digits. Moreover, our research involves the simulation of a typical sensory neuron, specifically a nociceptor, within our synaptic transistor. This research offers a novel avenue for the advancement of cost-effective three-terminal thin-film transistors tailored for neuromorphic applications.

Enhancing bio-photovoltaic cell efficiency: A study in transport property

Recently, bio-solar cells have garnered significant attention owing to their relatively high efficiency and cost-effectiveness, positioning them as alternative devices for solar energy harvesting. This study delves into the optical and electrical transport characteristics of a novel bilayer bio-solar cell using the total system transfer matrix method, theoretically. These bilayer bio-solar cells consist of two distinct layers of Chlorophyll-a and Chlorophyll-b, forming a heterojunction in the bio-solar cell architecture. Within these solar cells, photon absorption by the active layers of chlorophyll generates excitons and quasi-particles (bound electron and hole pairs), which subsequently diffuse through the collecting layer, resulting in significant recombination losses. The influence of the thickness of chlorophyll adsorbent active layers on the short circuit current density and quantum efficiency is examined through numerical calculations. Furthermore, we develop models for the solar cell parameters of thin film heterojunction photovoltaic devices based on Chlorophyll-a/Chlorophyll-b. The results indicate efficient short circuit current and quantum efficiency values (or power conversion efficiency) of 72 A/m2 and 3.30 %, respectively. It is demonstrated that optimizing the thickness of bio-solar cells based on these findings may enhance electron transport, leading to higher photocurrents and improved overall efficiency. These simulation outcomes pave the way for optimizing the thickness of bio-solar cells and advancing towards higher efficiencies.

Improved ammonia sensitivity and broadband photodetection by using PBTTT-C14/WS2-QDs nano-heterojunction based thin film transistor

An ambient temperature broadband photo-detector and ammonia (NH3) gas sensor devices are developed with PBTTT-C14/WS2-QDs heterojunction thin film. This composite thin film of PBTTT-C14 conjugate polymer and hydrothermally synthesized WS2-QDs have been deposited by high yield and cost-effective ‘floating film transfer method’ (FTM), which works as a channel (p-type) of the thin film transistor (TFT). To determine the NH3 sensing behavior of the TFT, different concentrations of analyte (0.5–20 ppm) have been exposed on the channel of the TFT, which shows the response of ∼ 50 % at 10 ppm ammonia concentration that is significantly higher than PBTTT-C14 only TFT. This improvement is made possible by the NH3-responsive depleted layer of polymer/QDs heterojunction, which varies widely in the presence of ammonia. As a consequence, the ON/OFF ratio, carrier mobility and threshold voltage (Vth) of the device changes in a wider range. Besides, this TFT based gas sensor is also highly selective to the other interfering gases. In addition to NH3 gas sensitivity, This TFT also shows very high photosensitivity under white light illumination that enhances ‘ON’ and ‘OFF’ current of the device by ∼ 2.2 and 70 times, respectively under one sun white light illumination, whereas Vth of the device is shifted by ∼ 22 V. Besides, the device shows quite fast response/ recovery time under NH3 gas exposure and light illumination.

Construction of S-scheme cyano-modified g-C3N4/TiO2 film with boosted charge transfer and highly hydrophilic surface for enhanced photocatalytic degradation of norfloxacin

Developing highly efficient and recyclable photocatalysts has been regarded as an attractive strategy to solve antibiotic contaminants. Herein, we designed and fabricated Cy-C3N4/TiO2 S-scheme heterojunction film with boosted charge transfer and a highly hydrophilic surface. The as-prepared heterojunction exhibited outstanding removal efficiency on tetracyclines and fluoroquinolone antibiotics (more than 80 % within 90 min). The removal rate of 300-Cy-C3N4/TiO2 on norfloxacin (NOR) was 2.12, and 1.59 times higher than that of pristine TiO2, C3N4/TiO2, respectively. The excellent photocatalytic performance of 300-Cy-C3N4/TiO2 was attributed to the highly hydrophilic surface and effective transfer and separation of carriers. Moreover, the NOR degradation pathways were proposed based on the results of density functional theory (DFT), and liquid chromatography-mass spectrometry. The toxicity assessment indicated the toxicity of intermediates can be remarkably alleviated. The DFT calculation and selective photo-deposition experiment demonstrated that an internal electric field was formed at the heterojunction interface, and the charge carriers migrated between Cy-C3N4 and TiO2 following an S-scheme transfer pathway. This research not only provides a promising method for tracking charge distribution on thin-film heterojunction photocatalysts but also helps us to design high-efficiency, and recyclable heterojunctions to solve antibiotic contaminants.

Impact of AlSnO Back-Channel Layer on the Performance of AlSnO/InSnZnO Heterojunction Thin-Film Transistors

Impact of AlSnO Back-Channel Layer on the Performance of AlSnO/InSnZnO Heterojunction Thin-Film Transistors

Influence of Deposition Parameters on Performance of Zn(O,S) Buffer Layer Deposited by Solution-Based Continuous Flow Reactor for CIGS Solar Cells

CdS thin films are commonly used as buffer layers in hetero-junction structured CIGS thin film solar cells. However, the toxicity of Cd has raised concerns regarding environmental safety and alternative materials have been explored. ZnS is a leading candidate to replace Cd, with the presence of Zn(O,S) impurities known to be required for efficient CIGS solar cell fabrication. In this study, we synthesized Zn(O,S) films using a solution-based deposition method combining a continuous flow reactor (CFR) with another solutionbased deposition method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the structural and physicochemical properties of the films, confirming the efficacy of the CFR process for depositing Zn(O,S) thin films in a short period of time. We successfully deposited Zn(O,S) thin films using the combined CFR process. Cd-free B:ZnO/Zn(O,S)/CIGS solar cells were fabricated on Mo-coated glass substrates to investigate the effects of experimental parameters, such as deposition time and method, on the performance of the Zn(O,S) buffer layer in the devices.

Performance Improvement of In-Ga-Zn Oxide Thin-Film Transistors by Excimer Laser Annealing.

We applied excimer laser annealing (ELA) on indium-zinc oxide (IZO) and IZO/indium-gallium-zinc oxide (IGZO) heterojunction thin-film transistors (TFTs) to improve their electrical characteristics. The IZO and IZO/IGZO heterojunction thin films were prepared by the physical vapor deposition method without any other annealing process. The crystalline state and composition of the as-deposited film and the excimer-laser-annealed films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. In order to further enhance the electrical performance of TFT, we constructed a dual-heterojunction TFT structure. The results showed that the field-effect mobility could be improved to 9.8 cm2/V·s. Surprisingly, the device also possessed good optical stability. The electron accumulation at the a-IZO/HfO, HfO/a-IGZO, and a-IGZO/gate insulator (GI) interfaces confirmed the a-IGZO-channel conduction. The dual-heterojunction TFT with IZO/HfO/a-IGZO-assisted ELA provides a guideline for overcoming the trade-off between high mobility (μ) and positive VTh control for stable enhancement mode operation with increased ID.

Effect of bath temperature on the efficiency and properties of Cu2O/ZnS/ZnO heterojunctions thin film prepared by electrodeposition and chemical bath deposition methods

A novel p-n type Cu2O/ZnS/ZnO heterojunction thin film was successfully fabricated by a combination of electrodeposition and chemical bath deposition techniques. The effect of bath temperature (T = 75, 80, 85, 90 °C) on the growth of ZnS layers was investigated. The influence of ZnS buffer layers on the properties and efficiency of the prepared heterojunction thin films were examined using XRD, FE-SEM, AFM, EDS, UV–Vis, and electrochemical measurements. The analysis of prepared films revealed that the Cu2O/ZnS/ZnO heterojunction exhibits a unique combination of hexagonal structure of ZnO and the cubic structure of Cu2O. It was found that all the heterojunction films exhibit the growth of composed pyramids and corner grains with a homogenous distribution. The optical band-gap of the deposited ZnS buffer layers decreased from 3.46 eV to 3.35 eV with an increase of bath temperature from 75 °C to 90 °C. Moreover, the obtained results revealed that the thicknesses and the surface roughness of ZnS buffer layers increased when bath temperature increased. Mott-Schottky results of the heterojunctions indicate a p-type semiconductor behavior for the Cu2O, while it was observed an n-type semiconductor behavior for the ZnO and ZnS layers. As a result, the photocurrent response of Cu2O/ZnO heterojunctions with ZnS layer insertion was enhanced from 0.175 to 0.730 mA, which can be attributed to the reduced electron transfer resistance, enlarged photo-generated (e−/h+) carrier separation efficiency, and enhanced light absorption due to the presence of ZnS buffer layers. These results highlight the advantages of the bath temperature on the deposition of ZnS for photoelectrochemical and solar cells applications.

Recent Advances and Prospects of Solution‐Processed Efficient Sb2S3 Solar Cells

AbstractSolar cells comprising earth‐abundant and non‐toxic elements with applicable bandgaps and high absorption coefficients have attracted considerable interest over the past several decades and are important devices for addressing the future demand for clean and renewable energy. Antimony sulfide (Sb2S3) crystal material effectively meets these requirements owing to its suitable bandgap, high absorption coefficient, high electron and hole mobilities, earth abundance, and excellent stability. Solution‐processed Sb2S3 films are essential to facilitate the fabrication of low‐cost, large‐scale, and high‐efficiency photovoltaic devices, but suffer from several shortcomings of large intrinsic defects, high interfacial barrier, and atomic mismatch, uncontrollable film thickness, and crystal orientation. In this review, a systematic overview of the fundamental properties of solution‐processed Sb2S3 materials is presented, and then interface engineering, defect passivation and control strategies, crystal orientation and modulation methods, device structure, and the performance of Sb2S3 solar cells are focused, highlighting the primary advancements and major challenges based on this technology. Finally, several creative perspectives and constructive innovation strategies for future research on Sb2S3 photovoltaic devices are provided, indicating a roadmap for the practical application of other inorganic semiconductor heterojunction thin film solar cells.

Strong thickness dependence in thin film photocatalytic heterojunctions: the ZnO-Bi2O3 case study.

Semiconductor heterojunctions are an effective way to achieve efficient photocatalysts, as they can provide an adequate redox potential with visible light excitation. Several works have reported synergistic effects with nanoparticle semiconductor materials. The question is still open for thin film heterojunctions formed by stacked layers, as photocatalysis is considered a surface phenomenon. To investigate if the internal layer really affects or modifies the photocatalytic properties of the external material, we analyze the thin film heterojunction with ZnO and Bi2O3 semiconductors deposited by spray pyrolysis in two configurations: substrate/ZnO/Bi2O3 and substrate/Bi2O3/ZnO. Microstructural analysis was performed to verify the formation of the physical junction of the materials and discard new ternary phases. The photocatalytic activity was analyzed as a function of the thickness of the layers under blue light irradiation. We determined the conduction and valence bands positions, the carrier concentrations, mobilities, Fermi levels, etc. that allowed us to distinguish two reaction mechanisms depending on the configuration. There is a strong compromise between the order and thickness of the layers with the photocatalytic activity. The internal electric field produced in the interface defines the route of the photogenerated charges, and therefore the photocatalytic response. Thus, well-designed thin film heterojunctions can indeed improve the photocatalytic activity of the surface layer.

PbS/p‐Si NW Heterojunction Thin Film Device for Room Temperature NH3 Detection

AbstractOne dimensional heterostructures with a definite interface where the host particle is decorated with the secondary material have been widely exploited for photocatalysis because of increased efficiency. Herein we report the synthesis of PbS−Si NW heterojunction using low temperature chemical bath deposition (CBD) techniques. Temperature, time, and the complexing agents of the growth solution were optimized to control the morphology and the resultant properties of the heterojunction thin films. These synthesized thin films exhibit high sensor responses in the presence of ammonia (NH3) due to an increase in the surface area and efficient p‐n junction formation. Additionally, there is a vast improvement in the detection limit of the sensors as our device was found to respond at concentrations as low as 0.1 ppm. Growth conditions are found to have significant influence on the sensor response.

High-Performance Self-Powered Quantum Dot Infrared Photodetector with Azide Ion Solution Treated Electron Transport Layer.

The demand for self-powered photodetectors (PDs) capable of NIR detection without external power is growing with the advancement of NIR technologies such as LIDAR and object recognition. Lead sulfide quantum dot-based photodetectors (PbS QPDs) excel in NIR detection; however, their self-powered operation is hindered by carrier traps induced by surface defects and unfavorable band alignment in the zinc oxide nanoparticle (ZnO NP) electron-transport layer (ETL). In this study, an effective azide-ion (N3 -) treatment is introduced on a ZnO NP ETL to reduce the number of traps and improve the band alignment in a PbS QPD. The ZnO NP ETL treated with azide ions exhibited notable improvements in carrier lifetime and mobility as well as an enhanced internal electric field within the thin-film heterojunction of the ZnO NPs and PbS QDs. The azide-ion-treated PbS QPD demonstrated a increase in short-circuit current density upon NIR illumination, marking a responsivity of 0.45 AW-1, specific detectivity of 4 × 1011 Jones at 950nm, response time of 8.2 µs, and linear dynamic range of 112dB.

Remarkably fast and reusable photocatalysis by UV annealed Cu2O–SnO2 p−n heterojunction

Powdered micro- or nano-particles photocatalyst has separation and recovery challenges, which may create a second pollution to environment and harmful to animals. To address those issues, SnO2, Cu2O and Cu2O–SnO2 p-n heterojunction thin films are formed on glass substrates using efficient co-sputtering method that is commonly employed for large-area high-definition display panel. Using first-order kinetics, 100 °C ultraviolet (UV) annealed Cu2O–SnO2 p-n heterojunction shows the superb fast degradation rate constant of 0.21 and 0.16 min−1 for methylene blue (MB) and methyl orange (MO) organic dyes, respectively, as photogenerated electron-hole pairs is increased. Record best degradation rate constants of 0.19 and 0.11 min−1 for respective MB and MO are still achieved even after four repeated cycles. The 100 °C UV annealed Cu2O–SnO2 film catalyst displays greater degradation efficiency in both dyes, reaching 100% degradation at room temperature after 30 and 35 min of illumination for MB and MO respectively. The scavenger experiments show that hydroxyl (·OH) and superoxide radicals (·O2−) are the major active species in the degradation of dye. The 100 °C UV annealed Cu2O–SnO2 film catalyst showed stability as well as reusability towards the dye degradation. As a result, the present work delivers an effective way to enhance the photocatalytic performance and also an easy recovery of the catalyst, which can be explored for various emerging pollutants.