MXene-Regulated Perovskite Vertical Growth for High-Performance Solar Cells.

Defects at the interfaces of perovskite (PVK) thin films are the main factors responsible for instability and low photoelectric conversion efficiency (PCE) of PVK solar cells (PSCs). Here, a SnO2 -MXene composite electron transport layer (ETL) is used in PSCs to improve interfacial contact and passivate defects at the SnO2 /perovskite interface. The introduced MXene regulates SnO2 dispersion and induces a vertical growth of PVK. The lattice matching of MXene and perovskite suppresses the concentration of interfacial stress, thereby obtaining a perovskite film with low defects. Compared with SnO2 -based device, the PCE of SnO2 -MXene-based device is improved by 15 % and its short-circuit current is up to 25.07 mA cm-2 . Furthermore, unencapsulated device maintained about 90 % of its initial efficiency even after 500 h of storage at 30-40 % relative humidity in ambient air. The composite ETL strategy provides a route to engineer interfacial passivation between metal halide perovskites and ETLs.

Interface Engineering of Silicon/Carbon Thin-Film Anodes for High-Rate Lithium-Ion Batteries.

Silicon is one of the most promising alternative active materials for next-generation lithium-ion battery (LIB) applications due to its advantage of high specific capacity. However, the enormous volume variations during lithiation/delithiation still remain to be an obstacle to commercialization. In this work, binder-free pure silicon and silicon/carbon (Si/C) multilayer thin-film electrodes, prepared by scalable one-step magnetron sputtering, are systematically investigated by an interlayer strategy. Herein, we present a rationally structural modification by an amorphous carbon film to enhance the electrical conductivity, mechanical integrity, and electrochemical performance of Si film-based LIBs. Therefore, to maintain the consistency of the direct-contact layer with the electrolyte and current collection, symmetrical Si/C/Si and Si/C/Si/C/Si/C/Si electrodes are deliberately designed to study the influence of embedded carbon. An anode with a carbon content of 10.38 wt % yields an initial discharge specific capacity of 1888.74 mAh g-1 and a capacity retention of 96.82% (1243.56 mAh g-1) after 150 cycles at a high current density of 4000 mA g-1. It also shows that the best rate capability remains 96.0% of the initial capacity in the 70th cycle. At last, three mechanisms are proposed for an in-depth understanding of the interface effect. This work offers a new perspective scheme toward Si/C-based LIBs with a capability of high rate and high energy density.

Improved performances of lithium-ion batteries using intercalated a-Si-Ag thin film layers as electrodes.

The laminated construction of an a-Si-Ag thin film electrode is demonstrated, which allows stabilization of the cycling performance of a silicon thin film layer in a lithium-ion battery. A silver thin film plays a determining role in the lithium insertion/extraction process and is incorporated between amorphous Si thin film layers (a-Si/Ag/a-Si), which results in not only high and stable capability, but also the best rate performance compared to that of other electrodes. For the electrode of a-Si/Ag/a-Si, a critical thickness of the silver layer (30 nm) is found; in this case, it exhibits the highest capacity retention of 70% after 200 cycles at a current density of 65.2 µA cm-2 within the voltage range of 0.01-1.5 V. It is demonstrated that for the a-Si/Ag/a-Si (140/30/140 nm) electrode, enhanced capacity (∼59.1%) is derived from the buffer effect and excellent conductivity of silver layer. Silver interlayer may represent a universal platform for relieving stress in a silicon electrode. In addition, its excellent electrical conductivity will decrease the charge transfer resistance of Si electrode for lithium-ion batteries.