Enhanced Device Performance Research Articles

Enhancing device performance of CsPbBr3 perovskite light-emitting diodes with Cs2CO3 modification layer and dual additives

This study presents the performance of CsPbBr3 perovskite light-emitting diodes (PeLEDs) with a cesium carbonate (CsCO3) modification layer and dual additives. With the Cs2CO3 modification layer, the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) hole transport layer was recrystallized to flatten the grains, reduce the series resistance, lower the impedance, and operate at a low level. It also has the lowest starting voltage at 3 V, which can release equivalent energy from electrons and holes. At 6 V, it has a maximum luminance of 16440 cd/m2 and an external quantum efficiency (EQE) of 1.56%.

2D Materials for Efficient Photodetection: Overview, Mechanisms, Performance and UV-IR Range Applications.

Two-dimensional (2D) materials have been widely used in photodetectors owing to their diverse advantages in device fabrication and manipulation, such as integration flexibility, availability of optical operation through an ultrabroad wavelength band, fulfilling of photonic demands at low cost, and applicability in photodetection with high-performance. Recently, transition metal dichalcogenides (TMDCs), black phosphorus (BP), III-V materials, heterostructure materials, and graphene have emerged at the forefront as intriguing basics for optoelectronic applications in the field of photodetection. The versatility of photonic systems composed of these materials enables their wide range of applications, including facilitation of chemical reactions, speeding-up of responses, and ultrasensitive light detection in the ultraviolet (UV), visible, mid-infrared (MIR), and far-infrared (FIR) ranges. This review provides an overview, evaluation, recent advancements as well as a description of the innovations of the past few years for state-of-the-art photodetectors based on two-dimensional materials in the wavelength range from UV to IR, and on the combinations of different two-dimensional crystals with other nanomaterials that are appealing for a variety of photonic applications. The device setup, materials synthesis, operating methods, and performance metrics for currently utilized photodetectors, along with device performance enhancement factors, are summarized.

Phase Variation of Ultrathin WO3 Electron‐Transport Layer Prepared by Scalable Langmuir–Blodgett Technique to Boost Efficiency of Dye Sensitized Solar Cells

In third‐generation solar cells, dye sensitized (DSCs) and perovskite (PSCs) both, the role of electron‐transport layers (ETLs) is to block hole transfer at fluorine‐doped tin oxide/mesoporous TiO2 interface, while efficiently transporting the electron at this interface. Conventional solution‐processed dense anatase TiO2 ETL is limited by its low electron mobility. WO3, despite having higher electron mobility and chemical stability, has seldom been used as ETL in DSCs/PSCs, owing to poor crystalline structure and interfacial charge transfer in ETLs prepared using existing methods. Herein this paper, ultrathin and uniform WO3 films of different crystalline structures, such as tetragonal (t‐), orthorhombic (o−), hexagonal (h−), and monoclinic (m−), prepared by scalable Langmuir–Blodgett method, are reported. The efficiency (η) of DSCs fabricated with ETL having high‐symmetry phases of WO3 (h‐WO3, o‐WO3, t‐WO3) is found to exceed the efficiency of devices having ETL of low‐symmetry WO3 phase (m‐WO3). Further, highest η ≈ 9.53%, tantamount to an improvement of 13%, is found in DSCs fabricated with ETL having a mixed phase of o‐ and t‐WO3 and surpassed η of devices based on TiO2 ETLs (8.4%). Herein, the role of structure/phase of WO3 ETLs toward enhancing device performance and outperforming the conventional TiO2 ETLs‐based DSCs is highlighted.

Highly Efficient Full van der Waals 1D p‐Te/2D n‐Bi2O2Se Heterodiodes with Nanoscale Ultra‐Photosensitive Channels

AbstractContinuous miniaturization of semiconductor devices is the key to boosting modern electronics development. However, this downscaling strategy has been rarely utilized in photoelectronics and photovoltaics. Here, in this work, a full‐van der Waals (vdWs) 1D p‐Te/2D n‐Bi2O2Se heterodiode with a rationally designed nanoscale ultra‐photosensitive channel is reported. Enabled by the dangling bond‐free mixed‐dimensional vdWs integration, the Te/Bi2O2Se type‐II diodes show a high rectification ratio of 3.6 × 104. Operating with 100 mV reverse bias or in a self‐power mode, the photodiodes demonstrate excellent photodetection performances, including high responsivities of 130 A W−1 (100 mV bias) and 768.8 mA W−1 (self‐power mode), surpassing most of the reports of other heterostructures. More importantly, a superlinear photoelectric conversion phenomenon is uncovered in these nanoscale full‐vdWs photodiodes, in which a model based on the in‐gap trap‐assisted recombination is proposed for this superlinearity. All these results provide valuable insights in light–matter interactions for further performance enhancement of photoelectronic devices.

Tunable anisotropic pulse photo response of ZrS3 crystal at cryogenic temperatures

Two-dimensional (2D) transition metal trichalcogenides (TMTCs) have been considered promising candidates for next-generation electronic devices. TMTCs containing quasi-one-dimensional chain structure, in contrast to two-dimensional (2D) Transition Metal Dichalcogenides (TMDCs), provide significant advantages in electronics and optoelectronics device modeling and engineering to enhance device performance. In this study, we present a pulse photoresponse application of a device based on the DVT-grown ZrS3 crystal at different cryogenic temperatures. It also includes anisotropy produced due to the layered growth of the TMC materials. Two types of contact arrangements were made to verify the anisotropic behaviour. The device was illuminated under light sources having different wavelengths (Blue-470 nm, Green-540 nm and Red-670 nm). It shows good stability under ambient conditions towards the variable wavelength source in both types of contact arrangements. The results indicate that ZrS3 is a potential candidate for optoelectronic devices even in uncommon conditions.

Enhanced performance of asymmetric supercapacitor based on NiZn-LDH@NiCoSe2 electrode materials

While supercapacitors have been widely studied as the next generation of energy storage devices, to develop active electrode materials for enhancing device performance is still challenging. Herein, we fabricated asymmetric supercapacitors based on NiZn-Layered double hydroxide (LDH) @NiCoSe2 hierarchical nanostructures as electrode materials. The NiZn-LDH@NiCoSe2 composites are deposited on Ni foam by a two-step strategy, in which NiZn-LDH nanosheets were firstly grown on Ni foam by hydrothermal method, and then NiCoSe2 particles were prepared by electrodeposition. Due to the synergistic effect between NiZn-LDH and NiCoSe2, excellent device performance was achieved. In a three-electrode system, the NiZn-LDH@NiCoSe2 exhibits a specific capacitance of 2980 F g−1 at 1 A g−1. Furthermore, the asymmetric supercapacitor of NiZn-LDH@NiCoSe2//activated carbon (AC) device was assembled, which exhibits the energy density of 49.2 Wh kg−1 at the power density of 160 W kg−1, with the capacity retention rate is 91% after 8000 cycles. The results indicates that NiZn-LDH@NiCoSe2 is a promising candidate as electrode materials for efficient energy storage devices.

Predictive materials and structures design of perpendicular magnetic anisotropy in magnetic tunnel junctions

The regular mechanism guiding for the selection of heavy metals (HMs) that adapt to different structures is thoroughly investigated. A predictive materials design framework is established based on the element distribution states analysis from high-resolution transmission electron microscopy (HRTEM) experiments to guide the complex design explorations for spin-orbit torque (SOT) devices. Based on surface free energy and formation enthalpy analyses, it is found that not only a critical HM material type but also an appropriate structure selection will contribute to the excellent magnetic properties required for SOT device control and design. Furthermore, the HM layers with high formation enthalpy value are critical for device performance enhancement, and HM layers with a high (low) surface free energy are better choices for the bottom (top) structure. The researches help to establish a predictive materials design framework, and is effective in designing memory cells with critical SOT effect.

Determination of dominant recombination site in perovskite solar cells through illumination‐side‐dependent impedance spectroscopy

AbstractPerovskite solar cells (PSCs) have attracted wide attention due to their capacity to achieve high‐power conversion efficiencies. However, the high trap‐assisted recombination taking place in the active layer leads to performance loss in PSCs. In particular, the excessive recombination at the interface between the perovskite active layer and the carrier selective contacts can be especially problematic. Therefore, the identification of the dominant recombination pathways in a given PSC architecture is of significant importance for the mitigation of losses and enhancement of device performance. Here, we introduce an approach for identifying the dominant recombination pathways in PSCs by applying illumination‐side‐dependent impedance spectroscopy (ISD‐IS) measurements on the devices with a semi‐transparent top electrode. We validate this technique using coupled ionic‐electronic numerical simulations and apply it experimentally on a standard PSC structure. Overall, this approach could be of significant importance for pinpointing the performance bottlenecks in PSC devices under operationally relevant conditions and providing a more detailed picture of the losses in a complete PSC device by examining its behaviors under illumination from both sides at different operation conditions, which could allow for a more targeted optimization strategy of PSCs to improve their performance.

Synergistic enhancement in optoelectrical anisotropy of polymer film at the air-liquid interface: An insight into molecular weight distribution dependent polymer alignment

In the context of polymer films, the degree of polymer chain orientation and alignment plays a crucial role in producing a high-performance electronic device owing to its quasi 1D nature. Therefore, a novel investigation on the dependency of optoelectrical anisotropy on polymer molecular weight distribution and its synergistic enhancement at the air-liquid interface was conducted using poly (3, 3′″ dialkylquarterthiophene)(PQT-12). We also explored PQT-12 (2:1), where 2:1 is the ratio by weight of the polymer obtained from hexane and CH2Cl2, respectively. In order to understand the mechanism of self-assembly and alignment of different molecular weight polymers at the air-liquid interface, Margonian flow effect was used to obtain oriented and aligned films that were investigated using multiple characterization techniques at the molecular, microscopic, and macroscopic levels. It was found that the film formed using PQT-12 (2:1) demonstrated a synergistic enhancement in dichroism (up to 55%), orientation, and ordering with synergistic enhancement in electrical anisotropy up to 11, mobility upto 11-fold and 2.5 fold respectively as compare to pristine PQT-12 (Hexane) and PQT-12 (CH2Cl2) isolated polymer in ambient condition. Thus, our study presents the an insight into the molecular weight distribution dependent alignment at air liquid interface for enhancement in device performance.

Brominated PEAI as Multi‐Functional Passivator for High‐Efficiency Perovskite Solar Cell

The interfaces of perovskite solar cells (PSCs) are well known to be rich in deep‐level carrier traps, which serve as non‐radiative recombination centers and limit the open‐circuit voltage (Voc) and power conversion efficiency (PCE) of PSCs. Defect chemistry and surface passivators have been researched extensively and mainly focused on the neutralization of uncoordinated lead or anion defects. Herein, a novel brominated passivator 2‐bromophenethylammonium iodide (2‐Br‐PEAI) is introduced for a multi‐functional passivation effect at the perovskite interface. The brominated species readily form 2D perovskite on top of the 3D perovskite and multi‐interact with the 3D perovskite surface. Apart from the halide vacancy filling and anion bonding ability, the Br atoms on the benzene ring can interact with the FA cations via strong hydrogen bonding N‐H ⋯ Br and interact with the [PbI6]4− inorganic framework. The interface defects in the PSCs are well passivated, minimizing non‐radiative recombination and enhancing device performance. As a result, a champion PCE of 24.22% was achieved with high Voc and fill factor. In addition, modified devices also showed enhanced operational stability (retention of >95% initial PCE after 400 h) and humidity resistance (>90% initial PCE maintained after 1500 h under ~50% RH).

Increased Efficiency of Organic Solar Cells by Seeded Control of the Molecular Morphology in the Active Layer

The performance of non‐fullerene, polymer bulk heterojunction (BHJ) organic photovoltaic devices has a significant correlation with the molecular morphology of the donor and acceptor. The authors show that small organic molecules coordinated to a metal oxide, an electron transport seed layer (ETSL), can profoundly modify the donor:acceptor molecular morphology of inverted organic photovoltaic (OPV) devices. Using grazing incidence wide angle X‐ray scattering (GIWAXS), the authors show that a PTB7‐Th:IEICO‐4F BHJ active layer has a higher degree of face‐on molecular alignment on ETSL‐1 (biphenyl‐4,4′‐dicarboxylic acid, coordinated to ZnO), whilst for naphthalene‐2,6‐dicarboxylic acid coordinated to ZnO (ETSL‐2), it is reduced. Devices of PTB7‐Th:IEICO‐4F BHJ prepared on ETSL‐1 had a 19.91% increase in the average power conversion efficiency (PCE), a 1.56% increase in the fill factor (FF), and a 16.66 ± 0.2% enhancement in the short circuit current density. The observed improvements are believed to be due to significant modifications to the oxide‐BHJ interfacial region of ETSL‐1, namely the elimination of nano‐ridges and defect centers, along with an enhanced wettability. These factors can be correlated with the enhanced device performances, leading to the conclusion that the modulation of the molecular morphology of donor:acceptor blends by ETSL‐1 has a broad impact on improving OPV cell efficiencies.

Origins and influences of metallic lead in perovskite solar cells

<h2>Summary</h2> Metallic lead (Pb⁰) impurities in metal-halide perovskites have attracted tremendous research concerns owing to their detrimental effects on perovskite solar cells (PSCs). However, the origins and influences of the Pb⁰ behind this issue have yet to be well understood. Herein, we show that Pb⁰ is hardly formed in the growth of halide perovskites but is easily postformed in the perovskite films with excess PbI₂. It is found that Pb⁰ impurities are decomposition byproducts of residual PbI₂ in perovskites under light or X-ray irradiation. Therefore, PSCs obtained using photodegraded PbI₂ films show large efficiency and stability losses. By contrast, the perovskite devices without detectable Pb⁰ impurities have a much better efficiency and stability. This work reveals the origins and influences of Pb⁰ in halide perovskites and provides a strategy for avoiding the formation of detrimental Pb⁰ byproducts, which would drive further enhancements in device performance of halide perovskite solar cells, detectors, etc.

Ferroelectric Polymer Nanofibers Reminiscent of Morphotropic Phase Boundary Behavior for Improved Piezoelectric Energy Harvesting (Small 15/2022)

Energy Harvesting In article number 2104472, Qing Wang, Chang Kyu Jeong, and co-workers study the enhancement of piezoelectric device performance using the morphotropic phase boundary behavior of polyvinylidene fluoride-based polymers related with its relaxor property. Moreover, it is proved that the characteristics are maintained in the nanofiber feature.

Top-Contact Pentacene-Based Organic Thin Film Transistor with a Rubrene Layer in between Pentacene-Electrode Interface

Top-contact pentacene-based organic thin-film transistor (OTFT) with a rubrene interlayer in between pentacene-electrode [Al, Au] interface is reported. A study of the interlayer behavior of rubrene shows enhanced device performance of OTFT than that of the conventional OTFTs with only metal source-drain electrodes [Al, Au]. The improved performances of the device are attributed to the smoother pentacene surface for high carrier injection and mobility and decrease in contact resistance of the device. The device with a rubrene interlayer in between pentacene/Au interface shows better field-effect mobility of 3.3 cm2 v−1 s−1, On/Off ratio of 1.22 × 107, the threshold voltage of −3.8 V, and sub-threshold-slope of 0.31 V decade−1 respectively.

Simulation of perovskite solar cells using molybdenum oxide thin films as interfacial layer for enhancing device performance

Organic-inorganic hybrid perovskite solar cells (PSCs) have the issue of interdiffusion at the interfaces that causes undesirable phenomena affecting device efficiency and stability. In this paper, we have investigated MoOx thin films as interlayer between the hole transport material and gold electrode and develop a model using the SCAPS solar cell simulator as a function of the interlayer film thickness to enhance device efficiency and stability. First, different thicknesses (2, 5, 10, 50, and 100 nm) of MoOx films were deposited on glass substrate by electron beam evaporation (e-beam) and their physical, chemical, optical, and electronic properties for PSC were examined. In this research, uniform, homogeneous and pinhole free MoOx films with high transmittance (˃ 80%), very low surface roughness, and resistivity were obtained from the 5 and 10 nm thick samples. In addition, the 10 nm film has shown the lowest photoluminescence emission. Using SCAPS solar cell simulation software and including MoOx thin films as passivation layer, the performance of the PSCs for a Pb-based and Pb-free perovskite absorber were modelled. Results showed that the 10 nm MoOx film is found to provide the best benefit to the device performance with enhanced power conversion efficiency (PCE) of 16.9% and 12.4% for the lead-based MAPb(I1-xBrx)3 and lead-free (MASnI3) perovskite solar cells, respectively.

Electronic and Excitonic Processes in Quantum Dot Light-Emitting Diodes.

A modified Langevin model has been proposed to study the electronic and excitonic dynamic processes in quantum dot light-emitting diodes (QLEDs), and the electroluminescence onset processes of the QLEDs under different charge-injection conditions have been explored. The simulation results are in good agreement with experimental curves, confirming the feasibility of this model. It is demonstrated that the formation of an exciton on the quantum dots (QDs) with one electron injected first followed by one hole is much more effective than that with the reverse sequence. That is, charging a QD with one electron first is more favorable for device performance enhancement, which is attributed to the low (high) Auger recombination rate of negative (positive) trions of commonly used type I QDs. Additionally, we demonstrate that enough electron injection is one of the prerequisites for high-performance QLEDs based on these type I QDs.

Quasi-vertical ε-Ga2O3 solar-blind photodetectors grown on p-Si substrates with Al2O3 buffer layer by metalorganic chemical vapor deposition

(002)-oriented ε-Ga2O3 thin films were heteroepitaxially grown on p-Si (111) substrates by metalorganic chemical vapor deposition (MOCVD). The introduction of Al2O3 buffer layer significantly improved the crystallinity and surface morphology of the ε-Ga2O3 films. Quasi-vertical deep ultraviolet photodetectors (UV-PDs) were fabricated and characterized based on ε-Ga2O3 films grown with and without the Al2O3 buffer layer. Compared with the n-Ga2O3/p-Si device, the n-Ga2O3/Al2O3/p-Si UV-PDs showed enhanced device performance under 254 nm illumination, including an ultralow dark current of 99.4 pA, a photo-to-dark current ratio of 104, a high ultraviolet responsivity of 8.1 A/W at −10 V, and a fast photo response with rise/decay time of 0.89 s/0.29 s. The improved device performance can be ascribed to the energy band engineering of n-Ga2O3/Al2O3/p-Si heterojunction. The Al2O3 layer works not only as a buffer layer but also as an electron-blocking layer, which allows holes to cross the heterojunction under the reverse bias. This work shows a promising method to develop high-performance ε-Ga2O3 UV-PDs on cost-effective Si substrates.

Enhancement of CZTS photovoltaic device performance with silicon at back-contact: A study using SCAPS-1D

Cu2ZnSnS4 (CZTS) is a promising photo-absorber material for photovoltaics (PV) applications. Molybdenum which is employed as a back-contact metal in the CZTS based PV devices, is not the best choice. In the present work, we have used one-dimensional Solar Cell Capacitance Simulator (SCAPS-1D) to study the effect of replacing molybdenum with p+-type silicon (Si), both in the crystalline and hydrogenated amorphous phases. The device models with these two phases of Si at the back-contact led to photoconversion efficiencies (η) of 16.83 and 21.85%, respectively. Moreover, with Si at the back-contact, the performance can be further enhanced to 22.45% with the introduction of selenium in the chalcogenide sub-lattice. These improved η values are due to improved short-circuit current and fill-factors; the open-circuit voltage remains unchanged. The reduction of Schottky barrier at the back-contact with the use of Si is resulting in these beneficial effects.

Epitaxial Topological Insulator Bi2Te3 for Fast Visible to Mid-Infrared Heterojunction Photodetector by Graphene As Charge Collection Medium.

Three dimensional topological insulators have a thriving application prospect in broadband photodetectors due to the possessed topological quantum states. Herein, a large area and uniform topological insulator bismuth telluride (Bi2Te3) layer with high crystalline quality is directly epitaxial grown on GaAs(111)B wafer using a molecular beam epitaxy process, ensuring efficient out-of-plane carriers transportation due to reduced interface defects influence. By tiling monolayer graphene (Gr) on the as-prepared Bi2Te3 layer, a Gr/Bi2Te3/GaAs heterojunction array prototype was further fabricated, and our photodetector array exhibited the capability of sensing ultrabroad photodetection wavebands from visible (405 nm) to mid-infrared (4.5 μm) with a high specific detectivity (D*) up to 1012 Jones and a fast response speed at about microseconds at room temperature. The enhanced device performance can be attributed to enhanced light-matter interaction at the high-quality heterointerface of Bi2Te3/GaAs and improved carrier collection efficiency through graphene as a charge collection medium, indicating an application prospect of topological insulator Bi2Te3 for fast-speed broadband photodetection up to a mid-infrared waveband. This work demonstrated the potential of integrated topological quantum materials with a conventional functional substrate to fabricate the next generation of broadband photodetection devices for uncooled focal plane array or infrared communication systems in future.

Influence of displacement and patterning of phase shifters for piston mode operation of temperature compensated surface acoustic wave resonators on SiO2/LiNbO3 structure

This paper discusses the influence of displacement and patterning of phase shifters for piston mode operation of the temperature compensated surface acoustic wave (SAW) resonator on SiO2/LiNbO3 structure. As the phase shifters, Cu metals placed on the top surface of SiO2 are considered. First, the conventional Cu stripes are chosen, and their displacement is considered from interdigital transducer (IDT) aperture edges. It is shown that achievable transverse mode suppression is almost identical when the stripe shape is adjusted for each case. Next, Cu dots are considered as patterned phase shifters. It is shown comparable transverse mode suppression is possible also for this case. However, relatively strong SAW lateral leakage occurs when they are placed above IDT fingers. These results indicate that location and pattern can be added as design parameters for the phase shifters on SiO2. It is favorable for further enhancement of total device performances.