Synergistic Ion-Anchoring Passivation for Perovskite Solar Cells with Efficiency Exceeding 24% and Ultra-Ambient Stability.

The high-density defect states existing at the grain boundaries and heterojunction interfaces induce nonradiative charge recombination and ion migration processes within perovskite film, which seriously impair the device efficiency and stability. Here, we propose a novel synergistic ion-anchoring passivation (SIP) strategy for high-performance perovskite solar cells, by designing a multifunctional molecule to heal the charged defects via electrostatic interactions. The anion and cation species of the multifunctional molecule are rationally screened via high-throughput DFT simulation and experimental verification, which act as efficient surface passivation agents to heal the lead- and iodine-related defects. As a result, the defect-less perovskite films deliver encouraging device power conversion efficiency >24% with negligible hysteresis. A remarkable open-circuit voltage (Voc) of 1.17 V was obtained with a Voc deficit of 370 mV, featuring the outstanding defect-passivation capability of the SIP strategy. Moreover, the SIP-treated devices show exceptional ambient stability and maintain 70% of the initial efficiency after 150 h of high humidity exposure (relative humidity 70%-80%). Our results highlight the importance of the rational design of passivation agents to realize high-performance perovskite electronics.

GaN/Gr (2D)/Si (3D) Combined High-Performance Hot Electron Transistors.

To overcome the problem of minority carrier storage time in bipolar transistors, a hot electron transistor (HET) has been proposed. This device has the advantage of high working speed and some complex logic functions can be completed by using one component. Here, we demonstrate a mixed-dimensional HET composed of GaN/AlN microwires, graphene (Gr), and Si. The electrons between GaN/AlN are injected into graphene by an F-N tunneling mechanism to achieve high speed hot electrons, then cross graphene by ballistic transport, and are collected in a nearly lossless manner through a low-barrier Si. Therefore, the device shows a record DC gain of 16.2, a collection efficiency close to the limit of 99.9% based on the graphene hot electron transistor (GHET), an emitter current density of about 68.7 A/cm2, and a high on/off current ratio reaching ∼107. Meanwhile, the current saturation range is wide, beyond those of most GHETs. It has potential applications as a power amplifier.

Two-In-One: End-Emitting Blue LED and Self-Powered UV Photodetector based on Single Trapezoidal PIN GaN Microwire for Ambient Light UV Monitoring and Feedback.

With the continuous miniaturization and integration of the semiconductor industry, micro/nanoscale integrated photonics has received extensive attention as a key technology for optical communication, optical storage, and optical interconnection. Here, a two-in-one device is reported with both unidirectional blue light emission and UV photodetection functions based on single trapezoidal PIN GaN microwire. By constructing a Fabry-Perot resonator cavity structure, the end-emitting blue light-emitting diode with a low turn-on voltage (≈0.97 V) and high color purity (full width at half maximum ≈22 nm) is implemented. Furthermore, benefiting from the slow growth rate of the semipolar planes on both sides of the trapezoidal microwire and the high diffuse reflectivity of the patterned substrate, the trapezoidal microwire sides can be used as a high-performance UV photodetector. In self-driven mode, the device exhibits a large responsivity (0.218 A W-1 ), high external quantum efficiency (83.31%) and fast response speed (rise/decay time of 0.48/0.98 ms). Finally, the prepared two-in-one device is successfully integrated into ambient light UV monitoring and feedback system and tested. This work provides a novel strategy to combine luminescence with photodetection, demonstrating high potential for applications, such as on-chip photonic integration, energy-saving communication and ambient light monitoring and feedback system.

Ga2O3 Quantum Dots with N-Doped Amorphous Carbon Fixed for Efficient Storage and Transfer of Lithium Ions by Introduction of Dopamine Hydrochloride.

The Ga2O3 anode has great potential due to its self-healing and high theoretical capacity in lithium-ion batteries. Like anodes with other transition metal oxides, the Ga2O3 anode has the problems of structural change and low electrical conductivity. The electrochemical performance of the Ga2O3 anode still needs to be improved. In this work, we synthesized a Ga2O3 quantum dots@N-doped carbon (Ga2O3-QD@NC) composite by hydrothermal reaction with a carbon source of dopamine hydrochloride, in which Ga2O3 quantum dots were dispersed in the interior of the amorphous carbon. Such a special structure is conducive to the high-speed migration of lithium ions and electrons and effectively inhibits volume expansion and agglomeration. Smaller and more uniform quantum dots facilitate efficient repair of the structure. Due to these advantages, the Ga2O3-QD@NC electrode has great electrochemical performance. The Ga2O3-QD@NC electrode has an initial discharge capacity of 1580 mAh g-1 with a high first Coulombic efficiency of 62.8% and a cycling capacity of 953 mAh g-1 under 0.1 A g-1. It even has a capacity of 460 mAh g-1 at 1 A g-1 after 300 cycles. This strategy can provide a new direction for the Ga2O3 anode in lithium-ion batteries with high capacity.

Correction: DLP printing of a flexible micropattern Si/PEDOT:PSS/PEG electrode for lithium-ion batteries.

Correction for 'DLP printing of a flexible micropattern Si/PEDOT:PSS/PEG electrode for lithium-ion batteries' by Xinliang Ye et al., Chem. Commun., 2022, 58, 7642-7645, https://doi.org/10.1039/D2CC01626E.

Improvement Strategies for Stability and Efficiency of Perovskite Solar Cells.

Recently, perovskites have garnered great attention owing to their outstanding characteristics, such as tunable bandgap, rapid absorption reaction, low cost and solution-based processing, leading to the development of high-quality and low-cost photovoltaic devices. However, the key challenges, such as stability, large-area processing, and toxicity, hinder the commercialization of perovskite solar cells (PSCs). In recent years, several studies have been carried out to overcome these issues and realize the commercialization of PSCs. Herein, the stability and photovoltaic efficiency improvement strategies of perovskite solar cells are briefly summarized from several directions, such as precursor doping, selection of hole/electron transport layer, tandem solar cell structure, and graphene-based PSCs. According to reference and analysis, we present our perspective on the future research directions and challenges of PSCs.

DLP printing of a flexible micropattern Si/PEDOT:PSS/PEG electrode for lithium-ion batteries.

We report on a free-standing 3D-printed Si/PEDOT:PSS/PEG electrode based on silicon nanoparticles (Si) as an active material for lithium-ion batteries (LIBs) that are fabricated by 3D printing via digital light processing (DLP). Compared with the Si electrode prepared by the traditional method, the 3D-printed Si/PEDOT:PSS/PEG electrode developed by DLP preserves a specific discharge capacity of 1658.4 mA h g-1, with a capacity fade of 0.3% per cycle at a current density of 800 mA g-1 after 125 cycles. This helps in maintaining its structural integrity and enables it to exhibit significantly high flexibility with an enhanced load of 4.2 mg cm-2. The resulting free-standing electrode shows that 3D printing has significant potential for application to a variety of LIB technologies.

'Stateful' threshold switching for neuromorphic learning.

Memristors have promising prospects in developing neuromorphic chips that parallel the brain-level power efficiency and brain-like computational functions. However, the limited available ON/OFF states and high switching voltage in conventional resistive switching (RS) constrain its practical and flexible implementations to emulate biological synaptic functions with low power consumption. We present 'stateful' threshold switching (TS) within the millivoltage range depending on the resistive states of RS, which originates from the charging/discharging parasitic elements of a memristive circuit. Fundamental neuromorphic learning can be facilely implemented based on a single memristor by utilizing four resistive states in 'stateful' TS. Besides the metaplasticity of synaptic learning-forgetting behaviors, multifunctional associative learning, involving acquisition, extinction, recovery, generalization and protective inhibition, was realized with nonpolar operation and power consumption of 5.71 pW. The featured 'stateful' TS with flexible tunability, enriched states, and ultralow operating voltage will provide new directions toward a massive storage unit and bio-inspired neuromorphic system.

Correction: 'Stateful' threshold switching for neuromorphic learning.

Correction for ''Stateful' threshold switching for neuromorphic learning' by Zhijian Zhong et al., Nanoscale, 2022, DOI: 10.1039/d1nr05502j.

A high-performance polarization-sensitive and stable self-powered UV photodetector based on a dendritic crystal lead-free metal-halide CsCu2I3/GaN heterostructure.

Polarization-sensitive photodetectors are the core of optics applications and have been successfully demonstrated in photodetectors based on the newly-emerging metal-halide perovskites. However, achieving high polarization sensitivity is still extremely challenging. In addition, most of the previously reported photodetectors were concentrated on 1D lead-halide perovskites and 2D asymmetric intrinsic structure materials, but suffered from being external bias driven, lead-toxicity, poor stability and complex processes, severely limiting their practical applications. Here, we demonstrate a high-performance polarization-sensitive and stable polarization-sensitive UV photodetector based on a dendritic crystal lead-free metal-halide CsCu2I3/GaN heterostructure. By combining the anisotropic morphology and asymmetric intrinsic structure of CsCu2I3 dendrites with the isotropic material GaN film, a high specific surface area and built-in electric field are achieved, exhibiting an ultra-high polarization selectivity up to 28.7 and 102.8 under self-driving mode and -3 V bias, respectively. To our knowledge, such a high polarization selectivity has exceeded those of all of the reported perovskite-based devices, and is comparable to, or even superior to, those of the conventional 2D heterostructure materials. Interestingly, the unsealed device shows outstanding stability, and can be stored for over 2 months, and effectively maintained the performance even after repeated heating (373K)-cooling (300K) for different periods of time in ambient air, indicating a remarkable temperature tolerance and desired compatibility for applications under harsh conditions. Such excellent performance and simple method strongly show that the CsCu2I3/GaN heterojunction photodetector has great potential in practical applications with high polarization-sensitivity. This work provides a new insight into designing novel high-performance polarization-sensitive optoelectronic devices.

Long and Ultrastable All-Inorganic Single-Crystal CsPbBr3Microwires: One-Step Solution In-Plane Self-Assembly at Low Temperature and Application for High-Performance Photodetectors.

As ideal building blocks for optoelectronic devices, one-dimensional (1D) single-crystal perovskite microwires (MWs) have received widespread attention due to their unique physical and chemical properties. Herein, a one-step solution in-plane self-assembly method is proposed to directly grow millimeter-long CsPbBr3 MWs with superior crystal quality at atmospheric environment. This method effectively avoids the use of toxic antisolvents. Furthermore, a MW-based photodetector is successfully fabricated, showing high photoresponsivity (20 A/W) and fast response (less than 0.3 ms). The stability of the photodetector is also confirmed by aging MW in air for 60 days, which shows a negligible change of photocurrent from 1.29 to 1.25 nA (-3 V) under the same experimental conditions. This work provides a low-cost and fast synthesis method for the preparation of single-crystal perovskite MWs and demonstrates their potential application for high-performance and stable photoelectronic device.

InGaN Nanorods Decorated with Au Nanoparticles for Enhanced Water Splitting Based on Surface Plasmon Resonance Effects.

Photoelectrochemical (PEC) water splitting has great application potential in converting solar energy into hydrogen energy. However, what stands in the way of the practical application of this technology is the low conversion efficiency, which can be promoted by optimizing the material structure and device design for surface functionalization. In this work, we deposited gold nanoparticles (Au NPs) with different loading densities on the surface of InGaN nanorod (NR) arrays through a chemical solvent route to obtain a composite PEC water splitting system. Enhanced photocatalytic activity, which can be demonstrated by the surface plasmon resonance (SPR) effect induced by Au NPs, occurred and was further confirmed to be associated with the different loading densities of Au NPs. These discoveries use solar water splitting as a platform and provide ideas for exploring the mechanism of SPR enhancement.

Bifunctional Ultrathin PCBM Enables Passivated Trap States and Cascaded Energy Level toward Efficient Inverted Perovskite Solar Cells.

Inverted perovskite solar cells (PSCs) with a C60 framework are known for their common drawback of low power conversion efficiency (PCE) of <20% because of nonradiative recombination and inefficient charge transport at their perovskite interfaces. Here, we report an ultrathin [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as a cap layer on perovskite films to overcome this issue. Such a functional cap layer efficiently passivates trap states and establishes a gradient energy level alignment onto perovskite, facilitating the efficient charge transfer and extraction. The as-fabricated inverted PSCs capped with such ultrathin PCBM exhibit a record PCE of 20.07%. After the storage under a N2 atmosphere for more than 500 h, the PCE of PSCs retains over 85% of its initial level. Our work provides an effective method to upgrade inverted PSCs with the C60 framework with improved efficiency and stability.

In Situ Conformal Coating of Polyaniline on GaN Microwires for Ultrafast, Self-Driven Heterojunction Ultraviolet Photodetectors.

Independent and zero-maintenance systems would be in urgent need in the near future internet of things. Here, we present high-performance, self-driven organic/inorganic heterojunction ultraviolet (UV) photodetectors (PDs) by in situ polymerization of polyaniline (PANI) on Gallium nitride microwires. The GaN microwires with a high crystalline quality are grown on patterned Si substrates by metal organic chemical vapor deposition. Using a facile in situ chemical polymerization method, PANI is conformally coated on the surface of GaN microwires. The constructed GaN/PANI hybrid microwire PD exhibits a high responsivity of 178 mA/W, a remarkable detectivity of 4.67 × 1014 jones, and an ultrafast UV photoresponse speed (rise time of 0.2 ms and fall time of 0.3 ms) under zero bias. The intimate heterojunction in the form of N-Ga-N bonds between GaN and PANI may account for the observed high performances. The presented self-driven microwire UV PDs featuring ultrahigh-speed (sub-millisecond) response to UV light may find applications in future nano/micro-photosensor networks.

Crystallographic plane and topography-dependent growth of semipolar InGaN nanorods on patterned sapphire substrates by molecular beam epitaxy.

A low-cost, high-efficiency, and catalyst-free method for fabricating well-aligned and uniform semipolar InGaN nanorods (NRs) by molecular beam epitaxy (MBE) is proposed using an optimized patterned sapphire substrate (PSS) with high Miller index crystallographic planes. The dense, obliquely aligned, and high-quality semipolar (11[combining macron]02) InGaN NRs are fabricated on hexagonal pyramid arrays of the PSS for the first time in this work. A unique semipolar (11[combining macron]02) and polar (0001) InGaN NR array composite structure is thus achieved on a hexagonal pyramid PSS. The connected, uniform, and obliquely aligned NRs are formed on the PSS with cylindrical arrays. The cylindrical and hexagonal pyramid arrays of PSSs are structured by the standard photolithography process and etching techniques. Both pattern topography and crystallographic plane of the PSS significantly affect the morphology, dimension, and crystallographic orientation of InGaN NRs. It is clearly demonstrated that the PSS with exposed high Miller index crystallographic planes, with well-organized step-terrace structures, facilitates the growth of ordered and dense semipolar InGaN NRs. This work contributes to the thorough understanding of the nucleation and growth mechanisms of InGaN NRs on a high Miller index plane of the PSS with different topographies, as well as of those of controllably fabricating dense and uniform semipolar NRs, thus facilitating the fabrication of NR-based optoelectronic devices with enhanced performance.

Correlations among morphology, composition, and photoelectrochemical water splitting properties of InGaN nanorods grown by molecular beam epitaxy.

The mechanism underlying the effect of growth condition on the morphology evolution of InGaN nanorods (NRs) has been systematically investigated. The increased Ga flux enhances both the axial and the radial growth at the growth stage. However, the changed Ga flux influences not only the growth but also the nucleation of InGaN NRs. At the nucleation stage, the increased Ga flux shortens the delay time for NR formation, and prolongs the growth stage for a fixed total growth time. Those two aspects result in the increase of NR diameter and height with the supplied Ga flux. In addition, the continuous nucleation is ended much earlier due to the accelerated saturation of substrate area with the increased Ga flux, resulting in a decreased final NR density. In addition to the morphology evolution with the Ga flux, the composition characteristic of InGaN NRs has been also studied. The In distribution of InGaN NRs depends critically on the NR diameter along the NR growth direction, and the NRs show a morphology-dependent In incorporation. Interestingly, the InGaN NRs discussed here show a radial Stark effect induced by the pinned Fermi level. The radial Stark effect shifts the absorption edge of the InGaN NRs toward longer wavelengths, makes the InGaN NRs attractive for photoelectrochemical water splitting applications. The photoelectrochemical measurements present a significant increase in the photocurrent with the increased total surface area of the InGaN NRs, which is due to the enhanced light absorption effects and the enlarged interfacial area of the semiconductor/electrolyte.

The mechanism of indium-assisted growth of (In)GaN nanorods: eliminating nanorod coalescence by indium-enhanced atomic migration.

Both well vertically aligned and uniformly separated (In)GaN nanorods (NRs) were successfully grown on Si(111) substrates by plasma-assisted molecular beam epitaxy. Effects of supplied indium (In) flux on the morphology of (In)GaN NRs were investigated systematically. The scanning electron microscopic analysis and transmission electron microscopic measurements revealed that the presence of In flux can help to inhibit NR coalescence and obtain well-separated (In)GaN NRs. By increasing the supplied In flux, the densities of (In)GaN NRs decreased and the axial growth rates increased. According to the energy dispersive X-ray spectrometry measurements and theoretical calculations, the increase of In content of the NRs enhanced Ga diffusion on the NR sidewalls, which resulted in an increased axial growth rate. A kinetic In-assisted growth model for the well-separated (In)GaN NRs is therefore proposed. The model explains that the presence of In flux not only reduces the density of (In)GaN NRs due to the increase in substrate surface migration of Ga adatoms at nucleation stage but also lead to a remarkable enhancement of axial growth rate at growth stage. Consequently, the NR coalescence was significantly suppressed. The results provide a demonstration of obtaining well-separated (In)GaN NRs and open up further possibility of developing (In)GaN NR-based optoelectronic devices.

Growth of InN Nanowires with Uniform Diameter on Si(111) Substrates: Competition Between Migration and Desorption of In Atoms.

The effects of the growth parameters on the uniformity and the aspect ratio of InN nanowires grown on Si(111) substrates have been studied systematically, and a modified quasi-equilibrium model is proposed. The growth temperature is of great importance for both the nucleation of the nanowires and the migration of In and N atoms, thus affecting the uniformity of the InN nanowires. In order to improve the uniformity of the InN nanowires, both traditional substrate nitridation and pre-In-droplet deposition have been implemented. It is found that the substrate nitridation is favorable for the nucleation of InN nanowires. However, the initial In atoms adhered to the substrate are insufficient to sustain the uniform growth of the InN nanowires. We have found that the initial In droplet on the substrate is not only advantageous for the nucleation of the InN nanowire, but also favorable for the In atom equilibrium between the initial In droplets and the direct In flux. Therefore, InN nanowires with a uniform aspect ratio and optimal diameter can be achieved. The results reported herein provide meaningful insights to understanding the growth kinetics during the InN nanowires growth, and open up great possibilities of developing high-performance group III-nitride-based devices.

Growth of InAs Quantum Dots on GaAs (511)A Substrates: The Competition between Thermal Dynamics and Kinetics.

The growth process of InAs quantum dots grown on GaAs (511)A substrates has been studied by atomic force microscopy. According to the atomic force microscopy studies for quantum dots grown with varying InAs coverage, a noncoherent nucleation of quantum dots is observed. Moreover, due to the long migration length of In atoms, the Ostwald ripening process is aggravated, resulting in the bad uniformity of InAs quantum dots on GaAs (511)A. In order to improve the uniformity of nucleation, the growth rate is increased. By studying the effects of increased growth rates on the growth of InAs quantum dots, it is found that the uniformity of InAs quantum dots is greatly improved as the growth rates increase to 0.14 ML s(-1) . However, as the growth rates increase further, the uniformity of InAs quantum dots becomes dual-mode, which can be attributed to the competition between Ostwald ripening and strain relaxation processes. The results in this work provide insights regarding the competition between thermal dynamical barriers and the growth kinetics in the growth of InAs quantum dots, and give guidance to improve the size uniformity of InAs quantum dots on (N11)A substrates.

Highly-efficient GaN-based light-emitting diode wafers on La 0.3 Sr 1.7 AlTaO6 substrates.

Highly-efficient GaN-based light-emitting diode (LED) wafers have been grown on La 0.3 Sr 1.7 AlTaO6 (LSAT) substrates by radio-frequency molecular beam epitaxy (RF-MBE) with optimized growth conditions. The structural properties, surface morphologies, and optoelectronic properties of as-prepared GaN-based LED wafers on LSAT substrates have been characterized in detail. The characterizations have revealed that the full-width at half-maximums (FWHMs) for X-ray rocking curves of GaN(0002) and GaN(10-12) are 190.1 and 210.2 arcsec, respectively, indicating that high crystalline quality GaN films have been obtained. The scanning electron microscopy and atomic force microscopy measurements have shown the very smooth p-GaN surface with the surface root-mean-square (RMS) roughness of 1.3 nm. The measurements of low-temperature and room-temperature photoluminescence help to calculate the internal quantum efficiency of 79.0%. The as-grown GaN-based LED wafers have been made into LED chips with the size of 300 × 300 µm(2) by the standard process. The forward voltage, the light output power and the external quantum efficiency for LED chips are 19.6 W, 2.78 V, and 40.2%, respectively, at a current of 20 mA. These results reveal the high optoelectronic properties of GaN-based LEDs on LSAT substrates. This work brings up a broad future application of GaN-based devices.