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Hybrid tin halides with formamidinium cations become a promising candidate for eco‐friendly solar cells, which achieves the best photovoltaic performance among various lead‐free perovskite solar cells (PSCs). Unfortunately, the low quality of perovskite layers and the oxidation of Sn2+ ions degrade the performance of devices, leading to an obviously lower power conversion efficiency (PCE) compare to hybrid lead halides. Additive engineering is a facile strategy for improving the quality of perovskite layers. In this work, the 2‐aminopyrazine (APZ) additive is investigated for depositing FA0.8PEA0.2SnI2.8Br0.2 layers, and corresponding PSCs are examined. It is found that the melting point of APZ additives drops below the annealing temperature of perovskite layers by the intermolecular interaction with formamidinium iodide (FAI). The melt phase at the grain boundaries encourages the diffusion of ions in the annealing process, leading to an improved quality of perovskite layers. And the formation of APZ‐SnI2 complex also inhibits the oxidation of Sn2+ ions. Consequently, the defect density and the recombination are significantly reduced in PSCs, resulting in an increase of PCEs from 11.4% to 13.0% and a simultaneous improvement of device stability. This work demonstrates a strategy for improving tin‐based PSCs based on melt assisted annealing and coordination interaction. [ABSTRACT FROM AUTHOR]

The ionic transport properties of LiNH2 under high pressures up to 30.8 GPa are systematically studied with alternate-current impedance spectra measurements and first-principles calculations. Two discontinuous changes of the electrical parameters can be found at approximately 12.0 and 20.0 GPa, which are attributed respectively to the pressure-induced structural phase transitions from the tetragonal phase to the monoclinic phase and the change of the transportation mechanism from mixed ionic and electronic conduction to pure ionic conduction. The conductivity of LiNH2 is decreased by one order of magnitude under high pressures due to the decreased migration rate of Li+ ions. Relaxation loss is found in LiNH2, which is caused by the long-distance diffusion of Li+ ions during the orientation polarization. The calculated ionic-migration potential barriers indicate that the energy required for Li+ ion migration increases with increasing pressure. The decrease in the amount of non-local electrons in the monoclinic phase led to the disappearance of electronic conduction after 20.0 GPa. [ABSTRACT FROM AUTHOR]

Tin diselenide (SnSe2) is a typical layered material of the main-group metaldichalcogenides, and exhibits superconductivity under pressure. In this work, the enhanced superconductivity of SnSe2 is reported in decompression and the key mechanism behind the decompression driven superconductivity enhancement is revealed. We explore SnSe2, transforming into superconductivity at ∼22 GPa, above which the superconductivity is robust up to 42.8 GPa. Interestingly, when the pressure gradually decreases to 14.0 GPa, the Tc increases monotonously from 6.0 K to 7.9 K. The observed unusual evolution of superconductivity was explained by a combination of pressure-manipulated carrier concentration and phonon softening during decompression by both experimental and theoretical studies. First-principles calculations reveal that interlayer Se–Se bonding is responsible for the series of changes. Our results demonstrate that interlayer coupling is critical for the superconductive behavior of the layered main-group metal dichalcogenides and provides a new platform to study the compressed superconductivity of layered compounds at low pressures. [ABSTRACT FROM AUTHOR]

For most resistive sensors, the change of carrier concentration usually dominates the conductivity change in the gas sensing process, while the role of carrier mobility change is difficult to reflect. In this work, a ternary alloyed MoS2−xSex gas sensing material with high crystal quality and a carrier mobility-dominated gas-sensing (CMDGS) mode has been successfully prepared by a one-pot solvothermal method for the detection of NO2 gas. It is found that the alloyed MoS2−xSex nanocomposites with the best crystal quality have the lowest charge transfer resistance and baseline resistance, which can be attributed to the high carrier mobility and low carrier effective mass. The response of the best MoS2−xSex sensor to 50 ppm NO2 is as high as 92.8 at room temperature (25 °C) with a response and a recovery time of 25 and 22 s, respectively, which are about 42.0 times those of the MoS2 sensor. The actual and theoretical detection limits reach 10 ppb and 37.1 ppt, respectively. This study reveals that the CMDGS mode can be realized by improving the crystal quality and establishing the local built-in electric field of the sensing materials, which is more progressive than the carrier concentration-dominated gas sensing (CDDGS) mode. [ABSTRACT FROM AUTHOR]

The hole transport layers are critical for collecting holes and suppressing recombination in perovskite solar cells, and metal oxides are superior due to their green synthesis and good ambient stability. Although gallium oxide is rarely applied as the hole transport layers of devices for the mismatch of valence bands with perovskite materials, copper dopants can provide an additional transport channel via their impurity levels. Herein, InxGa2−xO3 nanocrystals with copper dopants are synthesized as the hole transport material of perovskite solar cells by the hydrothermal method, and uniform hole transport layers can be deposited by spin‐coating at a low temperature of 100 °C. The energy position of impurity levels and the hole transport ability of hole transport layers can be regulated by incorporating indium ions. In the optimized condition, the efficiencies of devices increase from 19.6% to 21.4%, which is related to the improvement of the charge extraction process and carrier recombination process. And the photostability of devices can be improved simultaneously. This work provides an efficient hole transport material for inverted perovskite solar cells and demonstrates the regulation of transport channels via impurity levels. [ABSTRACT FROM AUTHOR]