Perovskite infiltration in cerium oxide and nickel oxide nanotubes*

The ability to fabricate nanotubes may lead to potential applications in the next generation of devices and other applications relying on enhanced surface area, low dimensionality, and structural control. For example, nanotubes can be used in photovoltaics, light-emitting devices, battery technology, biosensing/therapeutics, and MRI contrast agents.  In this work, we fabricate the arrays of nickel oxide nanotubes (NiO NTs) and cerium oxide nanotubes (CeO₂ NTs)  by using ZnO nanowires as a template. The ZnO nanowires were grown by a hydrothermal method followed by the deposition of CeO₂ or NiO to make CeO₂/ZnO or NiO/ZnO core-shell nanowires. The ZnO core was then removed by an etching process, forming CeO₂ NTs or NiO NTs. The inner diameter and length of the nanotubes are adjustable by the size selection of the ZnO nanowire template, while the CeO₂ or NiO deposition conditions control the shell thickness. This method allows for designing specific pore diameters and lengths in the nanotubes. The inner diameter in the CeO₂ NTs and NiO NTs serves as a nanoreactor vessel, allowing the infiltration of small molecules, nanoparticles, and precursors for the formation of perovskites in the nanotubes. Finally, 1D perovskites with a composition of (CH₃NH₂PbX₃ where X is the halogen Cl, Br, and I) were formed in NiO NTs and CeO₂ NTs. Applications of the encapsulated perovskites for LEDs and photovoltaics with enhanced stability were demonstrated.