Methylammonium lead iodide (MAPbI3) is an important light-harvesting semiconducting material for solar-cell devices.

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.

We have produced Fe-doped paramagnetic MAPbI 3 microwires by using a novel strategy involving a self-assembly growth process of [PbI 6 ] 4− octahedral chains in the presence of liquid water. Structural and morphological studies confirmed that after the dissociation and recrystallization process, the doped samples preserved both the perovskite structure with a tetragonal phase and a microwire shape, while X-ray photoelectron spectroscopy revealed the presence of mixed-valence Fe 3+ /Fe 2+ ions with negligible change in the PbI 6 cage environment and the maximum valence band position. From first-principles calculations, we determined that Fe 2+ ions are localized in the interstitial site while Fe 3+ ones are substitutional on Pb sites. The very high mobility and static dielectric constant, achieved by photogenerated charge carriers in MAPbI 3 , are suppressed for Fe-doped MAPbI 3 samples. These results are discussed based on a nonradiative recombination process assisted by phonons that is activated by the inclusion of the Fe ions. Our ab initio calculations support this model that can be also used to explain the quenching of the photoluminescence emission peaks. The successful insertion of dopants that can tune the perovskite's physical properties is important to the development of functional devices and is also able to open new potential applications such as in magnetic/semiconducting devices.

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.