Semimetallicity and Negative Differential Resistance from Hybrid Halide Perovskite Nanowires

In the rapidly progressing field of organometal halide perovskites, the dimensional reduction can open up new opportunities for device applications. Herein, taking the recently synthesized trimethylsulfonium lead triiodide (CH₃)₃SPbI₃ perovskite as a representative example, first‐principles calculations are carried out and the nanostructuring and device application of halide perovskite nanowires are studied. It is found that the 1D (CH₃)₃SPbI₃ structure is structurally stable, and the electronic structures of higher‐dimensional forms are robustly determined at the 1D level. Remarkably, due to the face‐sharing [PbI₆] octahedral atomic structure, the organic ligand‐removed 1D PbI₃ frameworks are also found to be stable. Moreover, the PbI₃ columns avoid the Peierls distortion and assume a semimetallic character, contradicting the conventional assumption of semiconducting metal‐halogen inorganic frameworks. Adopting the bundled nanowire junctions consisting of (CH₃)₃SPbI₃ channels with sub‐5 nm dimensions sandwiched between PbI₃ electrodes, high current densities and large room‐temperature negative differential resistance (NDR) are finally obtained. It will be emphasized that the NDR originates from the combination of the near‐Ohmic character of PbI₃‐(CH₃)₃SPbI₃ contacts and a novel NDR mechanism that involves the quantum‐mechanical hybridization between channel and electrode states. This work demonstrates the great potential of low‐dimensional hybrid perovskites toward advanced electronic devices beyond actively pursued photonic applications.     

Dual-Phase Stabilized Perovskite Nanowires for Reduced Defects and Longer Carrier Lifetime

1D perovskite materials are of significant interest to build a new class of nanostructures for electronic and optoelectronic applications. However, the study of colloidal perovskite nanowires (PNWs) lags far behind those of other established perovskite materials such as perovskite quantum dots and perovskite thin films. Herein, a dual-phase passivation strategy to synthesize all-inorganic PNWs with minimized surface defects is reported. The local phase transition from CsPbBr₃ to CsPb₂Br₅ in PNWs increases the photoluminescence quantum yield, carrier lifetime, and water-resistivity, owing to the energetic and chemical passivation effect. In addition, these dual-phase PNWs are employed as an interfacial layer in perovskite solar cells (PSCs). The enhanced surface passivation results in an efficient carrier transfer in PSCs, which is a critical enabler to increase the power conversion efficiency (PCE) to 22.87%, while the device without PNWs exhibits a PCE of 20.74%. The proposed strategy provides a surface passivation platform in 1D perovskites, which can lead to the development of novel nanostructures for future optoelectronic devices.     

Reversible Transformation between CsPbBr3 Perovskite Nanowires and Nanorods with Polarized Optoelectronic Properties

CsPbX₃ (X = Cl, Br, I) perovskite nanowires and nanorods are important 1D and quasi 1D semiconductor nanomaterials. They have shown significant prospect in optic and optoelectronic applications, especially for their adaptability to flexible devices, good carrier transport performance, polarized absorption, and emission properties. Due to the high dependence of the property to the morphology, it is crucial to develop synthesis methods with continuous diameter and length tunability of the 1D/quasi 1D perovskites. In this report, a feasibly room temperature synthesis method was developed for ultrathin CsPbX₃(X = Cl, Br, I) perovskite nanowires. By aging the CsPbBr₃ nanowires (≈2*500 nm) under ambient condition with proper concentration and time, the nanowires are transformed to nanorods with controllable diameter and length. Reversibly, the nanorods can be transformed back to nanowires. Equilibrium mechanism is adopted to understand the morphology evolution, and hopefully could be generally applied to many other nano materials. The polarized optoelectronic properties of the nanowires and nanorods are interpreted by a model based on the two-channel anisotropies measurement. Polarized light detectors constructed by oriented assembled nanowires are fabricated to demonstrate their application potentials.     

Solution‐Processable Near‐Infrared–Responsive Composite of Perovskite Nanowires and Photon‐Upconversion Nanoparticles

Organolead halide perovskites (OHPs) have shown unprecedented potentials in optoelectronics. However, the inherent large bandgap has restrained its working wavelength within 280–800 nm, while light at other regions, e.g., near‐infrared (NIR), may cause drastic thermal heating effect that goes against the duration of OHP devices, if not properly exploited. Herein, a solution processable and large‐scale synthesis of multifunctional OHP composites containing lanthanide‐doped upconversion nanoparticles (UCNPs) is reported. Upon NIR illumination, the upconverted photons from UCNPs at 520–550 nm can be efficiently absorbed by closely surrounded OHP nanowires (NWs) and photocurrent is subsequently generated. The narrow full width at half maximum of the absorption of rare earth ions (Yb³⁺ and Er³⁺) has ensured high‐selective NIR response. Lifetime characterizations have suggested that Förster resonance energy transfer with an efficiency of 28.5% should be responsible for the direct energy transfer from UCNPs to OHP NWs. The fabricated proof‐of‐concept device has showcased perfect response to NIR light at 980 and 1532 nm, which has paved new avenues for applications of such composites in remote control, distance measurement, and stealth materials.     

钙钛矿结构

本文详细介绍了理想钙钛矿结构及其各种变体。     

Perovskite crystallization

In recent years,perovskite solar cells(PSCs)have attrac-ted tremendous attention due to their high power conver-sion efficiencies(PCEs)and tailorable optoelectronic proper-ties.Up to now,the certified PCE of lab-scale PSCs has climbed up to 25.5％(see https://www.nrel.gov/pv/cell-effi-ciency.html).However,there still exists a large efficiency gap between small-area devices and large-area solar modules.The main reason refers to the difference between morpho-logy and crystallinity caused by different perovskite film forma-tion.To address this issue,it is of great necessity to make high-quality perovskite films.Currently,efforts are being de-voted to exquisitely modulating the nucleation and crystal growth of perovskite films[1-3].     

钙钛矿太阳电池吸收层制备工艺

有机/无机杂化钙钛矿太阳电池因具有高光吸收系数、高转换效率以及低制备成本等优点引起了科学界的广泛关注.综述了近年来有机/无机杂化钙钛矿吸收层几种制备工艺的研究进展,重点分析了目前应用较为广泛且制备工艺相对简单的一步溶液法和两步连续沉积法的工艺条件对钙钛矿薄膜质量及太阳电池光伏性能的影响,并详细介绍了几种制备工艺存在的主要问题及其调控的研究现状.此外,对后续工艺中的有机空穴传输材料及其溶剂、添加剂对钙钛矿太阳电池稳定性的影响及其调控的研究现状进行了简要阐述.为更好地提高钙钛矿太阳电池的效率和长期稳定性,制备工艺的优化和创新是未来钙钛矿太阳电池发展的趋势.     

MBE-Grown Cubic ZnS Nanowires

Ultrathin ZnS nanowires (NWs) were grown on a sapphire (0001) substrate at 430°C by the molecular-beam epitaxy (MBE) technique using self-assembled Au droplets as the catalyst. It was found that these NWs mainly consist of the cubic phase but a small portion was in the hexagonal phase. The analysis of the temperature-dependent band-edge (BE) emission of these NWs and that of a ZnS thin film revealed that the energy shift of the interband transition on temperature in ZnS is mainly attributed to the electron–phonon interactions. The observed blue shift of the BE emission of ZnS NWs could be quantitatively explained by the confinement of the excited excitons in the NW geometry.     

Defects in GaN Nanowires

High‐resolution transmission electron microscopy (HRTEM) and cross‐sectional transmission electron microscopy (XTEM) are used to characterize common defects in wurtzite GaN nanowires grown via a vapor–liquid–solid (VLS) mechanism. HRTEM shows that these nanowires contain numerous (001) stacking defects interspersed with small cubic GaN regions. Using XTEM, bicrystalline nanowires are discovered with twofold rotational twin axes along their growth directions, and are found to grow along high‐index directions or vicinal to low‐index planes. We propose a defect‐mediated VLS growth model to qualitatively account for the prevalence of these extended defects, and discuss the implications of these defects for nanowire growth kinetics and device behavior.     

Ferroic Halide Perovskite Optoelectronics

Metal halide perovskites (MHPs) as one of the most active materials gained tremendous attention in the past decade because of their outstanding performance in optoelectronics. Owing to their perovskite structure, ferroelectricity is anticipated in this class of materials. However, whether MHPs are ferroelectric or not remains elusive. Recently, discussion regarding ferroelasticity in MHPs has been also raised. In addition, ionic motion and structural dynamics are well known in MHPs. The interplay of these phenomena including electric polarization, strain, ionic motion, and structural dynamics can have a significant impact on optoelectronics. Therefore, understanding the mechanism behind these phenomena and their interactions is critical in addressing the controversy about ferroicity of MHPs and developing functional devices. Here, the current findings about MHP's ferroicity are summarized and evaluated and a perspective for the future is provided. It is suggested that ionic motion and associated phenomena, coupled with ferroic behavior, are the main drivers behind MHPs functionality. The challenges are also discussed in probing MHPs’ ferroicity and what new measurement modalities are needed to fully understand and characterize MHP behavior. Finally, it is discussed how ferroic and strain can affect the optoelectronic performance of MHPs and how they can be used for engineering of higher performance devices.     

硅纳米线的电学特性

总结了硅纳米线在电学特性方面的研究进展,重点分析了本征及掺杂硅纳米线的载流子浓度与迁移率、场发射及电子输运特性。研究表明通过对硅纳米线进行掺杂可提高载流子浓度及迁移率、场发射和电子输运性能,随硅纳米线直径的减小其电学性能增强。因此,硅纳米线在场效应晶体管及存储元件等纳米器件方面具有极大的应用前景。     

室温合成的钙钛矿量子点及其电致发光二极管

采用室温合成法制备出CsPbBr3钙钛矿量子点,并采用乙酸乙酯对量子点进行了一次、二次和三次清洗,以控制其表面配体密度。然后,利用合成并经过清洗的钙钛矿量子点制备了结构为ITO/PEDOT∶PSS/PTAA/CsPbBr3 QD/TPBi/LiF/Al的电致发光二极管(QLED)。研究了经不同清洗次数的量子点材料制备的器件的光电性能。结果表明,清洗2次的量子点在电荷注入与溶液稳定性之间得到平衡,利用其制备的钙钛矿QLED获得了最大亮度为1405cd/m²、外量子效率为0.6%、色坐标为(0.127,0.559)的绿光发射。     

W5O14 Nanowires

We report on the synthesis of quasi‐1D W₅O₁₄ crystals using NiI₂ as a growth promoter. Photoelectron spectroscopy revealed the metallic conductivity of the W₅O₁₄ nanowires, which was also confirmed by direct‐transport measurements on a double‐stranded nanowire. Scanning electron microscopy and transmission electron‐diffraction data are correlated with details of crystal growth revealing the possible mechanism of the formation of this rarely synthesized phase, which was reported as a homogeneous phase only in 1978 by McColm et al., and in the meantime has been declared as a compound that is rare.     

Impedance Conditions in Metal Nanowires

Journal of Communications Technology and Electronics - Approximate equations for the conductivity of metal nanowires of finite width and finite thickness and finite-thickness films are obtained in...