CH3NH3PbI3‐xClx is a commonly used chemical formula to represent the methylammonium lead halide perovskite fabricated from mixed chlorine‐ and iodine‐containing salt precursors. Despite the rapid progress in improving its photovoltaic efficiency, fundamental questions remain regarding the atomic ratio of Cl in the perovskite as well as the reaction mechanism that leads to its formation and crystallization. In this work we investigated these questions through a combination of chemical, morphological, structural and thermal characterizations. The elemental analyses reveal unambiguously the negligible amount of Cl atoms in the CH3NH3PbI3‐xClx perovskite. By studying the thermal characteristics of methylammonium halides as well as the annealing process in a polymer/perovskite/FTO glass structure, we show that the formation of the CH3NH3PbI3‐xClx perovskite is likely driven by release of gaseous CH3NH3Cl (or other organic chlorides) through an intermediate organometal mixed halide phase. Furthermore, the comparative study on CH3NH3I/PbCl2 and CH3NH3I/PbI2 precursor combinations with different molar ratios suggest that the initial introduction of a CH3NH3+ rich environment is critical to slow down the perovskite formation process and thus improve the growth of the crystal domains during annealing; accordingly, the function of Cl− is to facilitate the release of excess CH3NH3+ at a relatively low annealing temperatures.

All-solid-state flexible supercapacitors based on a carbon/MnO(2) (C/M) core-shell fiber structure were fabricated with high electrochemical performance such as high rate capability with a scan rate up to 20 V s(-1), high volume capacitance of 2.5 F cm(-3), and an energy density of 2.2 × 10(-4) Wh cm(-3). By integrating with a triboelectric generator, supercapacitors could be charged and power commercial electronic devices, such as a liquid crystal display or a light-emitting-diode, demonstrating feasibility as an efficient storage component and self-powered micro/nanosystems.

WO3–x@Au@MnO2 core–shell nanowires (NWs) are synthesized on a flexible carbon fabric and show outstanding electrochemical performance in supercapacitors such as high specific capacitance, good cyclic stability, high energy density, and high power density. These results suggest that the WO3–x@Au@MnO2 NWs have promising potential for use in high-performance flexible supercapacitors.

The applications of organotin halide perovskites are limited because of their chemical instability under ambient conditions. Upon air exposure, Sn2+ can be rapidly oxidized to Sn4+, causing a large variation in the electronic properties. Here, the role of organic cations in degradation is investigated by comparing methylammonium tin iodide (MASnI3) and formamidinium tin iodide (FASnI3). Through chemical analyses and theoretical calculations, it is found that the organic cation strongly influences the oxidation of Sn2+ and the binding of H2O molecules to the perovskite lattice. On the one hand, Sn2+ can be easily oxidized to Sn4+ in MASnI3, and replacing MA with FA reduces the extent of Sn oxidation; on the other hand, FA forms a stronger hydrogen bond with H2O than does MA, leading to partial expansion of the perovskite network. The two processes compete in determining the material's conductivity. It is noted that the oxidation is a difficult process to prevent, while the water effect can be largely suppressed by reducing the moisture level. As a result, FASnI3‐based conductors and photovoltaic cells exhibit much better reproducibility as compared to MASnI3‐based devices. This study sheds light on the development of stable Pb‐free perovskite optoelectronic devices through new material design.

Owing to the rapidly growing global energy consumption, the development of high-performance power sources has become an urgent and increasing demand in various fi elds such as portable electronics and sensor networks. [1][2][3] As a result of their excellent characteristics, such as superior power density, fast charge/discharge rates, and long cycle lifetime, supercapacitors (SCs, also known as electrochemical capacitors or ultracapacitors), which bridge the gap between high specifi c energy batteries and high specifi c power conventional capacitors, have been employed as state-of-the-art energy storage systems and widely used in consumer electronics, backup power sources, and pacemakers. [4][5][6][7] Since the energy density is proportional to the capacitance (specifi c or areal capacitance), C , and square of the cell voltage, Δ U , which can be calculated asan enhancement of energy density can be achieved by maximizing the capacitance and/or the operating voltage of SCs. [ 8 ] Compared with carbon-based materials, pseudo-capacitive materials such as transition metal oxides and conducting polymers [9][10][11][12][13] show much higher capacitive performance. Although the use of an organic electrolyte is one possible approach to increasing the operating voltage up to 4 V, [14][15][16] poor ionic conductivity will result in high equivalent series resistance (ESR) and low power output. Alternatively, asymmetric supercapacitors (ASCs) provide an environmentally friendly and effective approach to improving the energy density of SCs, as the operating voltage can be broadened by combining two appropriate electrodes with different potential windows. [ 8 , 17-19 ] For safety, weight, and environmental reasons, a solid-state electrolyte is superior to a liquid one, and is greatly desired for portable and wearable consumer electronics.Many metal oxide negative electrode materials, such as molybdenum oxide (MoO 3-x ) [ 20 ] and iron oxide, [ 21 ] show a superior performance to carbon-based materials. However, the low electronic conductivity of metal oxides profoundly affects their electrochemical performance. In order to solve this problem, the use of high-specifi c-area and high-conductivity nanomaterials, such as zinc oxide and tungsten oxide (WO 3-x ) nanowires, [ 12 ] as a scaffold to load electrochemically active materials is proposed as a viable solution. [ 22 ] Polyaniline (PANI) could be a positive electrode material because of its high capacitive performance and simple synthesis method. In this Communication, we report a simple and effi cient method of growing MoO 3-x /WO 3-x core/shell nanowires on carbon fabric as a negative electrode, assembled with PANI nanowires on carbon fabric as a positive electrode, to fabricate high performance all-solid-state ASCs with H 3 PO 4 /poly(vinyl alcohol) (PVA) as the electrolyte. Electrochemical measurements indicated that the fabricated ASCs can be cycled reversibly between 0 and 1.9 V. Furthermore, the whole cell (including electrodes, separator, and electrolyte) exhibits a...