Combinatorial composition-gradient and -aligned CsPb(Br1−<i>x</i>I<i>x</i>)3 films by IR-laser MBE

We investigated the combinatorial synthesis and characterization of a halide perovskite CsPb(Br1−xIx)3 composition-gradient film deposited on a SrTiO3(001) substrate using infrared laser molecular beam epitaxy. In halide perovskite materials, the diffusion speed of the halogen ions is high, making it difficult to form a continuous composition-gradient film. This is because halogen ions diffuse across the entire film surface, making it impossible to specify the anion composition that changes at each position. In this study, a contact-shadow mask process was introduced to suppress the interdiffusion of halogen ions. Consequently, a CsPb(Br1−xIx)3 composition-gradient and -aligned film in which the chemical composition of CsPbBr3 and CsPbI3 changed digitally was formed and systematically characterized for the optical bandgap and photoluminescence emission wavelength with respect to the chemical composition of the halogen ion. This deposition process is expected to be promising for exploring halide perovskite materials with complex chemical compositions, such as triple-cation halide perovskites.