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In this paper, mesoporous nitrogen-doped TiO2 microspheres were prepared by a template-free solvothermal method. The nitrogen-doped TiO2 mesoporous spheres show higher visible-light photocatalytic activity than the undoped TiO2. The dual role of urea helps the formation of a mesoporous structure and the doping of nitrogen into TiO2 to be completed simultaneously during the solvothermal process. The amount of urea shows the crucial effect on the mesoporous structure and nitrogen doping in TiO2.

Although unprecedented conversion efficiency has been achieved in organic–inorganic hybrid perovskite solar cells (PSCs), their long‐term stability has remained a major issue in their transition. Here, we demonstrate a highly‐stable CH3NH3PbI3 (MAPbI3) perovskite using a green self‐assembly (SA) process that provides a major breakthrough in resolving this issue. In this process, the hydrophobic polymer, poly(methyl methacrylate) (PMMA), is introduced into the 2D layered MAPbI3 perovskite intermediates, resulting in chemical coordination and self‐assembly into 3D perovskite grains with PMMA coated along the grain boundaries. The bilayer grain boundary effectively blocks moisture corrosion thereby significantly improving the stability of MAPbI3 perovskite. Further, PMMA is found to reduce the trap density by electronically compensating the iodide vacancy along the boundary, which decreases the charge recombination and improves the open circuit voltage of PSCs. The PSCs comprising the MAPbI3−PMMA layer show excellent stability under high moisture conditions, exhibiting no phase change under ≈70% humidity for over 31 days (approximately 500% higher compared to state‐of‐the‐art) and excellent performance in 50–70% humidity for over 50 days.

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NASICON-type Li 1+x Al x Ge 2-x (PO 4 ) 3 solid state lithium ionic conductors were synthesized by a sol-gel method using citric acid and ethylene glycol. The obtained precursors were sintered at various temperatures and the NASICON-type single phase was observed in a range of x = 0-0.6. The highest electrical conductivity was obtained for Li 1.4 Al 0.4 Ge 1.6 (PO 4 ) 3 sintered at 900 • C for 11 h in air. The total conductivity was 1.22×10 −3 S cm −1 at 25 • C, and the bulk and grain boundary conductivities were estimated by impedance profile analysis to be 1.70×10 −3 and 4.30×10 −3 S cm −1 , respectively. Sintered pellets of Li 1.4 Al 0.4 Ge 1.6 (PO 4 ) 3 were immersed in distilled water, saturated LiCl aqueous solution, and a saturated LiCl and LiOH aqueous solution at 50 • C for one week; X-ray diffraction patterns of these samples dried at 220 • C under vacuum showed no significant change from that of the pristine sample. The electrical conductivity of Li 1.4 Al 0.4 Ge 1.6 (PO 4 ) 3 was decreased to 1.4×10 −4 S cm −1 at 25 • C by immersion in distilled water, while immersion in the saturated LiCl aqueous solution increased the conductivity to 4.95×10 −3 S cm −1 at 25 • C. Li 1.4 Al 0.4 Ge 1.6 (PO 4 ) 3 was stable in the saturated LiCl and LiOH aqueous solution. Li 1.4 Al 0.4 Ge 1.6 (PO 4 ) 3 was unstable in contact with Li metal and Li-In alloy, but was stable in contact with Li 7 Ti 5 O 12 .

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