Miaoqiang Lyu

Resistive Switching Behavior in Organic–Inorganic Hybrid CH3NH3PbI3−xClx Perovskite for Resistive Random Access Memory Devices

The CH3 NH3 PbI3- x Clx organic-inorganic hybrid perovskite material demonstrates remarkable resistive switching behavior, which can be applicable in resistive random access memory devices. The simply designed Au/CH3 NH3 PbI3- x Clx /FTO structure is fabricated by a low-temperature, solution-processable method, which exhibits remarkable bipolar resistive switching and nonvolatile properties.

Stable Hematite Nanosheet Photoanodes for Enhanced Photoelectrochemical Water Splitting

A vertically grown hematite nanosheet film modified with Ag nanoparticles (NPs) and Co-Pi cocatalyst exhibits a remarkably high photocurrent density of 4.68 mA cm(-2) at 1.23 V versus RHE. The Ag NPs leads to significantly improved light harvesting and better charge transfer, while the Co-Pi facilitates a highly stable oxygen evolution process. This photoelectrode design provides more efficient photoelectrochemical systems for solar-energy conversion.

Stable and Low‐Cost Mesoscopic CH3NH3PbI2Br Perovskite Solar Cells by using a Thin Poly(3‐hexylthiophene) Layer as a Hole Transporter

Mesoscopic perovskite solar cells using stable CH3 NH3 PbI2 Br as a light absorber and low-cost poly(3-hexylthiophene) (P3HT) as hole-transporting layer were fabricated, and a power conversion efficiency of 6.64 % was achieved. The partial substitution of iodine with bromine in the perovskite led to remarkably prolonged charge carrier lifetime. Meanwhile, the replacement of conventional thick spiro-MeOTAD layer with a thin P3HT layer has significantly reduced the fabrication cost. The solar cells retained their photovoltaic performance well when they were exposed to air without any encapsulation, presenting a favorable stability. The combination of CH3 NH3 PbI2 Br and P3HT may render a practical and cost-effective solid-state photovoltaic system. The superior stability of CH3 NH3 PbI2 Br is also promising for other photoconversion applications.

Bifunctional resistive switching behavior in an organolead halide perovskite based Ag/CH3NH3PbI3−xClx/FTO structure

Organolead halide perovskite materials open up a new era for developing low-cost and high efficiency solar cells due to their simple and inexpensive fabrication process, superior light absorption coefficient, and excellent charge mobility. In addition to solar cells, hybrid perovskites have also seen dynamic advances with rapidly expanded applications to many other exciting fields including electronic and optical devices. Here, we demonstrate a new type of bifunctional resistive switching memory device based on a very simple bilayer structure of Ag and a CH3NH3PbI3−xClx perovskite material on an FTO substrate with both digital and analog resistive switching characteristics. The bi-stable resistive switching behavior with reliable endurance over 103 times and a retention time of 4 × 104 s demonstrates that the Ag/CH3NH3PbI3−xClx/FTO device can be a promising candidate for RRAM. In the low voltage sweeping region, surprisingly, analog resistive switching behavior with potentiation and depression characteristics was also observed, which can be useful in neuromorphic computing device applications. The possible Ag conducting filaments formed by redox reactions of the Ag electrode may play a key role in this newly observed resistive switching phenomenon.

Transition from the Tetragonal to Cubic Phase of Organohalide Perovskite: The Role of Chlorine in Crystal Formation of CH3NH3PbI3 on TiO2 Substrates

The role of chlorine in the superior electronic property and photovoltaic performance of CH3NH3PbI(3-x)Clx perovskite has attracted recent research attention. Here, we study the impact of chlorine in the perspective of the crystal structure of the perovskite layer, which can provide important understanding of its excellent charge mobility and extended lifetimes. In particular, we find that in the presence of chlorine (PbCl2 or CH3NH3Cl), when CH3NH3PbI3 films are deposited on a TiO2 mesoporous layer instead of a planar TiO2 substrate, a stable cubic phase rather than the commonly observed tetragonal phase is formed in CH3NH3PbI3 perovskite at room temperature. The relative peak intensity of two major facets of cubic CH3NH3PbI3 crystals, (100)C and (200)C facets, can also be easily tuned, depending on the film thickness. Furthermore, compared with pristine CH3NH3PbI3 perovskite films, in the presence of chlorine, CH3NH3PbI3 crystals grown on planar substrates exhibit strong preferred orientations on (110)T and (220)T facets.

An Innovative Freeze-Dried Reduced Graphene Oxide Supported SnS2 Cathode Active Material for Aluminum-Ion Batteries

Rechargeable aluminum-ion batteries (AIBs) are attractive new generation energy storage devices due to its low cost, high specific capacity, and good safety. However, the lack of suitable electrode materials with high capacity and enhanced rate performance makes it difficult for real applications. Herein, the preparation of 3D reduced graphene oxide-supported SnS2 nanosheets hybrid is reported as a new type of cathode material for AIBs. The resultant material demonstrates one of the highest capacities of 392 mAh g-1 at 100 mA g-1 and good cycling stability. It is revealed that the layered SnS2 nanosheets anchored on 3D reduced graphene oxide network endows the composite not only high electronic conductivity but also fast kinetic diffusion pathway. As a result, the hybrid material exhibits high rate performance (112 mAh g-1 at 1000 mA g-1 ). The detailed characterization also verifies the intercalation and deintercalation of relatively large chloroaluminate anions into the layered SnS2 during the charge-discharge process, which is important for better understanding of the electrochemical process of AIBs.

Low-temperature processed solar cells with formamidinium tin halide perovskite/fullerene heterojunctions

A new type of lead-free, formamidinium (FA)-based halide perovskites, FASnI2Br, are investigated as light-harvesting materials for low-temperature processed p–i–n heterojunction solar cells with different configurations. The FASnI2Br perovskite, with a band-gap of 1.68 eV, exhibits optimal photovoltaic performance after low-temperature annealing at 75 °C. By using C60 as electron-transport layer, the device yields a hysteresis-less power conversion efficiency of 1.72%. The possible use of an inorganic MoOx film as a new type of independent hole-transport layer for the present tin-based perovskite solar cells is also demonstrated.

Configuration-centered photovoltaic applications of metal halide perovskites

Metal halide perovskites, particularly lead halide perovskites, have seen extraordinary breakthroughs in photovoltaics with power conversion efficiency swiftly surging to over 22% in the past few years, demonstrating their huge potential for rivalry with crystalline silicon solar cells in terms of production cost and performance for the future photovoltaic market. While a number of recent reviews have provided excellent overviews on the advances of metal halide perovskite materials in photovoltaics, herein we review the perovskite photovoltaics from the perspective of configuration and device design. More specifically, this review is centered on four configurations: rigid perovskite photovoltaics, flexible perovskite photovoltaics, semi-transparent perovskite photovoltaics and tandem perovskite photovoltaics. This review is going to meet the demand behind the industry and scientific community for the realistic application of perovskite photovoltaics in various requirements and circumstances.

Bias-dependent effects in planar perovskite solar cells based on CH3NH3PbI3−xClx films

A unique bias-dependent phenomenon in CH3NH3PbI(3-x)Cl(x) based planar perovskite solar cells has been demonstrated, in which the photovoltaic parameters derived from the current-voltage (I-V) curves are highly dependent on the initial positive bias of the I-V measurement. In FTO/CH3NH3PbI(3-x)Cl(x)/Au devices, the open-circuit voltage and short-circuit current increased by ca. 337.5% and 281.9% respectively, by simply increasing the initial bias from 0.5 V to 2.5 V.

Switched photocurrent on tin sulfide-based nanoplate photoelectrodes

A new type of SnS2 nanoplate photoelectrode is prepared by using a mild wet-chemical method. Depending on the calcination temperatures, SnS2 -based photoelectrodes can either retain their n-type nature with greatly enhanced anodic photocurrent density (ca. 1.2 mA cm-2 at 0.8 V vs. Ag/AgCl) or be completely converted into p-type SnS to generate approximately 0.26 mA cm-2 cathodic photocurrent density at -0.8 V vs. Ag/AgCl. The dominance of sulfur and tin vacancies are found to account for the dramatically different photoelectrochemical behaviors of n-type SnS2 and p-type SnS photoelectrodes. In addition, the band structures of n-type SnS2 and p-type SnS photoelectrodes are also deduced, which may provide an effective strategy for developing SnS2 /SnS films with controllable energy-band levels through a simple calcination treatment.