Efficient Green Quasi-Two-Dimensional Perovskite Light-Emitting Diodes Based on Mix-Interlayer

Recently, quasi-two-dimensional (Q-2D) perovskites have received much attention due to their excellent photophysical properties. Phase compositions in Q-2D perovskites have obvious effect on the device performance. Here, efficient green perovskite light-emitting diodes (PeLEDs) were fabricated by employing o-fluorophenylethylammonium bromide (o-F-PEABr) and 2-aminoethanol hydrobromide (EOABr) as the mix-interlayer ligands. Phase compositions are rationally optimized through composition and interlayer engineering. Meanwhile, non-radiative recombination is greatly suppressed by the introduction of mix-interlayer ligands. Thus, green PeLEDs with a peak photoluminescence quantum yield (PLQY) of 81.4%, a narrow full width at half maximum (FWHM) of 19 nm, a maximum current efficiency (CE) of 27.7 cd/A, and a maximum external quantum efficiency (EQE) of 10.4% were realized. The results are expected to offer a feasible method to realize high-efficiency PeLEDs.

Simulation Study of the Use of AlGaN/GaN Ultra-Thin-Barrier HEMTs with Hybrid Gates for Achieving a Wide Threshold Voltage Modulation Range

In this work, novel hybrid gate Ultra-Thin-Barrier HEMTs (HG-UTB HEMTs) featuring a wide modulation range of threshold voltages (VTH) are proposed. The hybrid gate structure consists of a p-GaN gate part and a MIS-gate part. Due to the depletion effect assisted by the p-GaN gate part, the VTH of HG-UTB HEMTs can be significantly increased. By tailoring the hole concentration of the p-GaN gate, the VTH can be flexibly modulated from 1.63 V to 3.84 V. Moreover, the MIS-gate part enables the effective reduction in the electric field (E-field) peak at the drain-side edge of the p-GaN gate, which reduces the potential gate degradation originating from the high E-field in the p-GaN gate. Meanwhile, the HG-UTB HEMTs exhibit a maximum drain current as high as 701 mA/mm and correspond to an on-resistance of 10.1 Ω mm and a breakdown voltage of 610 V. The proposed HG-UTB HEMTs are a potential means to achieve normally off GaN HEMTs with a promising device performance and featuring a flexible VTH modulation range, which is of great interest for versatile power applications.

Improved device performance of recessed-gate AlGaN/GaN HEMTs using by in-situ N2O radical treatment

In this work, the N2O radicals in-situ treatment on gate region has been employed to improve device performance of recessed-gate AlGaN/GaN high-electron-mobility transistors (HEMTs). The samples after gate recess etching were treated by N2O radicals without physical bombardment. After in-situ treatment (IST) processing, the gate leakage currents decreased by more than one order of magnitude compared to the sample without IST. The fabricated HEMTs with the IST process show a low reverse gate current of 10-9 A/mm, high on/off current ratio of 108, and high fT×Lg of 13.44 GHz·μm. A transmission electron microscope (TEM) imaging illustrates an oxide layer with a thickness of 1.8 nm exists at the AlGaN surface. X-ray photoelectron spectroscopy (XPS) measurement shows that the content of the Al-O and Ga-O bonds elevated after IST, indicating that the Al-N and Ga-N bonds on the AlGaN surface were broken and meanwhile the Al-O and Ga-O bonds formed. The oxide formed by a chemical reaction between radicals and the surface of the AlGaN barrier layer is responsible for improved device characteristics.

Low Dark Current and Performance Enhanced Perovskite Photodetector by Graphene Oxide as an Interfacial Layer

Organic–inorganic hybrid perovskite photodetectors are gaining much interest recently for their high performance in photodetection, due to excellent light absorption, low cost, and ease of fabrication. Lower defect density and large grain size are always favorable for efficient and stable devices. Herein, we applied the interface engineering technique for hybrid trilayer (TiO2/graphene oxide/perovskite) photodetector to attain better crystallinity and defect passivation. The graphene oxide (GO) sandwich layer has been introduced in the perovskite photodetector for improved crystallization, better charge extraction, low dark current, and enhanced carrier lifetime. Moreover, the trilayer photodetector exhibits improved device performance with a high on/off ratio of 1.3 × 104, high responsivity of 3.38 AW−1, and low dark current of 1.55 × 10−11 A. The insertion of the GO layer also suppressed the perovskite degradation process and consequently improved the device stability. The current study focuses on the significance of interface engineering to boost device performance by improving interfacial defect passivation and better carrier transport.

Sulfurization of Electrodeposited Sb/Cu Precursors for CuSbS2: Potential Absorber Materials for Thin-Film Solar Cells

CuSbS2, as a direct bandgap semiconductor, is a promising candidate for fabricating flexible thin-film solar cells due to its low grain growth temperature (300°C–450°C). Uniform and highly crystalline CuSbS2 thin films are crucial to improving device performance. However, uniform CuSbS2 is difficult to obtain during electrodeposition and post-sulfurization due to the “dendritic” deposition of Cu on Mo substrates. In this study, Sb/Cu layers were sequentially pulse electrodeposited on Mo substrates. By adjusting the pulse parameters, smooth and uniform Sb layers were prepared on Mo, and a flat Cu layer was obtained on Sb without any dendritic clusters. A two-step annealing process was employed to fabricate CuSbS2 thin films. The effects of temperature on phases and morphologies were investigated. CuSbS2 thin films with good crystallinity were obtained at 360°C. As the annealing temperature increased, the crystallinity of the films decreased. The CuSbS2 phase transformed into a Cu3SbS4 phase with the temperature increase to 400°C. Finally, a 0.90% efficient solar cell was obtained using the CuSbS2 thin films annealed at 360°C.

The Rational Control of Precursor Concentration in Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) have attracted tremendous attention due to their ideal optoelectronic properties, such as high color purity, high fluorescence quantum yield, and tunable light color. The perovskite layer plays a decisive role in the performance of PeLEDs and the solvent engineering of the perovskite layer is the key technological breakthrough in preparing high quality films. In this study, we have proposed the strategy of adding different amounts of solvents to the perovskite precursor solution to optimize the morphology of perovskite films and device performance. As a result, with the decreasing concentration of perovskite precursor solution, the perovskite film morphology is smoother and more favorable for carrier injection and combing, which induces an enhanced external quantum efficiency. The maximum luminance of PeLEDs was increased from 1667 cd/m2 to 9857 cd/m2 and the maximum current efficiency was increased from 6.7 cd/A to 19 cd/A. This work provides a trend to achieve improved film morphology and device performance for perovskite optoelectronic devices.

A viewpoint on material and design considerations for oesophageal stents with extended lifetime

Oesophageal stents are meshed tubular implants designed to maintain patency of the oesophageal lumen and attenuate the symptoms of oesophageal cancer. Oesophageal cancers account for one in twenty cancer diagnoses and can lead to dysphasia, malnutrition and the diminishment of patient quality of life (QOL). Self-expanding oesophageal stents are the most common approach to attenuate these symptoms. Recent advances in oncological therapy have enabled patient survival beyond the lifetime of current devices. This introduces new complications for palliation, driving the need for innovation in stent design. This review identifies the factors responsible for stent failure. It explores the challenges of enhancing the longevity of stent therapies and outlines solutions to improving clinical outcomes. Discussions focus on the role of stent materials, construction methods, and coatings upon device performance. We found three key stent enhancement strategies currently used; material surface treatments, anti-migratory modifications, and biodegradable skeletons. Furthermore, radioactive and drug eluting stent designs were identified as emerging novel treatments. In conclusion, the review offers an overview of remaining key challenges in oesophageal stent design and potential solutions. It is clear that further research is needed to improve the clinical outcome of stents and patient QOL.