Liquid water induces the formation of 1D morphology. 1D assembly of [PbI6]4− octahedra intercalated with (CH3NH3·H2O)+ cations is formed. When the water molecules are removed the 1D assembly change to 3D perovskite but keeping its wire morphology.

Methylammonium lead iodide (MAPbI3) is a very promising semiconducting material for photovoltaic applications. Despite extensive research and tremendous progress, basic charge transport properties are still being debated. Combining first-principles calculations and macroscopic and local measurements, we have investigated the structural, optical, thermal, and electrical transport (ac/dc) properties of MAPbI3 hot-pressed pellets through the tetragonal-to-cubic phase transition. Thermal analysis and X-ray diffraction experiments confirm the tetragonal-to-cubic phase change around T S = 56 °C, which is often close to the working temperature of photovoltaic devices. The ac/dc electrical resistivities of the tetragonal phase indicate a metallic-like behavior as a function of temperature followed by an abrupt decrease in the cubic phase just above T S. In contrast to the abrupt changes observed in the electrical properties, the bandgap energy is barely affected across the phase transition. Similarly, local measurements obtained by means of nuclear magnetic resonance confirm a continuous variation in the lattice parameters and site symmetry (207Pb and 127I) across the structural phase transition. Density functional theory calculations combined with electrical characterizations indicate that iodine and/or unintentionally incorporated hydrogen interstitials influence decisively the charge transport activation energy in the cubic phase. In light of these findings, the unusual electrical resistivity behavior across the phase transition is discussed taking the grain boundary effects into consideration.

Halide perovskite CsPbBr3 quantum dots (QDs) were synthesized via supersaturated recrystallization process and deposited on the surface of TiO2 microtubes forming local nano-heterostructures. Structural, morphological, and optical characterizations confirm the formation of heterostructures comprised of TiO2 microtube decorated with green-emitting CsPbBr3 nanocrystals. Optical characterizations reveal the presence of two band gap energies corresponding to CsPbBr3 (2.34 eV) and rutile-TiO2 (2.97 eV). Time-resolved photoluminescence decays indicate different charge dynamics when comparing both samples, revealing the interaction of CsPbBr3 QDs with the microtube surface and thus confirming the formation of local nano-heterostructures. The voltage–current measurements in the dark show an abrupt decrease in the electrical resistivity of the CsPbBr3/TiO2 heterostructure reaching almost 95% when compared with the pristine TiO2 microtube. This significant increase in the electrical conductivity is associated with charge transfer from perovskite nanocrystals into the semiconductor microtube, which can be used to fine tune its electronic properties. Besides controlling the electrical conductivity, decoration with semiconducting nanocrystals makes the hollow heterostructure photoluminescent, which can be classified as a multifunctionalization in a single device.

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