Charge Transport in MAPbI₃ Pellets across the Tetragonal-to-Cubic Phase Transition: The Role of Grain Boundaries from Structural, Electrical, and Optical Characterizations

Abstract

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.

Tailoring the Optical, Electronic, and Magnetic Properties of MAPbI3 through Self-Assembled Fe Incorporation

“…DC electrical resistivity measurements by using the four-probe method were also carried out (not shown), which are in agreement with impedance spectroscopy measurements. The electrical resistivity for the MAPbI 3 polycrystalline microwires is slightly higher than the value reported in the literature for MAPbI 3 pellets at room temperature, but it is considerably lower compared to the resistivity of single crystals, , possibly due to the grain boundary effects. The behavior of the electrical resistivity as a function of the light intensity is presented in Figure b,e for pure and doped perovskite microwires, respectively.…”

UV-Assisted Conversion of 2D Ruddlesden–Popper Iodide Perovskite Nanoplates into Stable 3D MAPbI3 Nanorods

“…The origin of the very low intensity peak around 7.7° (marked by filled circles in Figure c) is not clear to us; it might have originated from another phase of the material. Note that the synthesis of phase-pure NPls is hard to realize. , The reflections around 14.1 and 28.5° (marked by filled triangles in Figure c) correspond to the (110) and (220) planes of bulk MAPbI 3 perovskite, respectively, which originated within the RP NPls. − …”

“…On the other hand, the intensity of the bulk 3D peaks of MAPbI 3 around 14.1, 28.2, 28.5,31.6, and 31.9° became prominent. In the final sample (after 10 h of UV irradiation), reflection around 14.0, 14.1, 20, 23.5, 24.5, 28.1, 28.5, 31.6, 31.9, 40.5, 42.8, and 43.1° corresponding to the (002), (110), (200), (211), (202), (004), (220), (114), (310), (224), (411), and (314) crystallographic planes, respectively, of the tetragonal MAPbI 3 (space group I 4/mcm) is observed (see Figures d and S6b of Supporting Information), which is in good agreement with the previous reports. − …”

Temperature and pressure induced structural transitions of lead iodide perovskites

“…18 The ato b-phase transition is close to second order as the volume change is continuous. 77,90 However, a thermal hysteresis observed during the heating step suggests that the nature of the transition could be of rstorder. 90,91 Furthermore, the whole phase transition process was found to be reversible during cooling and heating cycles.…”