Epitaxial CH3NH3Pb(Br1-xIx)3 thin films on CH3NH3PbBr3 single crystal substrates formed by physical vapor deposition

Abstract

We have succeeded in fabrication of lead-halide single crystalline heterostructures by physical vapor deposition. By coevaporating CH3NH3I and PbI2 onto atomically flat CH3NH3PbBr3 (001) surfaces at room temperature, pseudomorphic perovskite alloy CH3NH3Pb(Br1-xIx)3 thin films are epitaxially formed. Formation of alloys proceeds by interdiffusion of I and Br ions via halide ion vacancies. Continuous ion exchange results in exponential decay in iodine composition x with a time constant of about one month. We suggest that large lattice mismatch between CH3NH3PbI3 and CH3NH3PbBr3 may accelerate alloying driven by the ion migration.