Ultrafast Carrier Diffusion in Perovskite Monocrystalline\nFilms

Monocrystalline\nperovskite materials exhibit superior properties\ncompared with polycrystalline perovskites, including lower defect\ndensity, minimal grain boundaries, and enhanced carrier mobility.\nNevertheless, the preparation of large-area, high-quality single-crystal\nfilms, which could prove invaluable for photoelectronic applications,\nremains a significant challenge. The study of how their unique properties\ngo beyond polycrystalline thin films is still missing. In our experiment,\nusing polarization-selective transient absorption microscopy, we directly\nobserved the spatial carrier transportation in methylammonium lead\niodide (CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, MAPbI<sub>3</sub>) strip-shaped monocrystalline ultrathin films. Ultrafast carrier\ndiffusion transportation was observed. The monocrystalline carrier\ndiffusion coefficient <i>D</i> (∼22 cm<sup>2</sup> s<sup>–1</sup>) is an order of magnitude higher than that\nin polycrystalline films. Anisotropic carrier diffusion of the MAPbI<sub>3</sub> single crystal has been discovered. It is also discovered\nthat the electrons and holes are of different anisotropy and diffusion\nspeed. This ultralong carrier transport inside the monocrystalline\nfilm provides solid support for the development of perovskite based\nphotoelectronic devices.