The fields of photovoltaics, photodetection and light emission have seen tremendous activity in recent years with the advent of hybrid organic-inorganic perovskites. Yet, there have been far fewer reports of perovskite-based field-effect transistors. The lateral and interfacial transport requirements of transistors make them particularly vulnerable to surface contamination and defects rife in polycrystalline films and bulk single crystals. Here, we demonstrate a spatially-confined inverse temperature crystallization strategy which synthesizes micrometre-thin single crystals of methylammonium lead halide perovskites MAPbX3 (X = Cl, Br, I) with sub-nanometer surface roughness and very low surface contamination. These benefit the integration of MAPbX3 crystals into ambipolar transistors and yield record, room-temperature field-effect mobility up to 4.7 and 1.5 cm2 V−1 s−1 in p and n channel devices respectively, with 104 to 105 on-off ratio and low turn-on voltages. This work paves the way for integrating hybrid perovskite crystals into printed, flexible and transparent electronics.

The search for new superconductors capable of carrying loss-free current has been a research theme in condensed matter physics for the past decade. Among superconducting compounds, titanates have not been pursued as much as Cu (3d) (cuprate) and Fe (3d) (pnictide) compounds. Particularly, Ti-based compounds or electron systems with a special 3d filling are thought to be promising candidates as high-T superconductors, but there has been no report on such pure Ti-based superconducting titanates. With the advent of thin-film growth technology, stabilizing new structural phases in single-crystalline thin films is a promising strategy to realize physical properties that are absent in the bulk counterparts. Herein, we report the discovery of unexpected superconductivity in orthorhombic-structured thin films of TiO, a 3d electron system, which is in strong contrast to the conventional semiconducting corundum-structured TiO. This is the first report of superconductivity in a titanate with a pure 3d electron configuration. Superconductivity at 8 K was observed in the orthorhombic TiO films. Leveraging the strong structure-property correlation in transition-metal oxides, our discovery introduces a previously unrecognized route for inducing emergent superconductivity in a newly stabilized polymorph phase in epitaxial thin films.