Formation of Stable Metal Halide Perovskite/Perovskite Heterojunctions

Heterojunctions underpin the design and performance of virtually all devices based on conventional semiconductors. While metal halide perovskites have received intense attention for applications in photoconversion and optoelectronics, these devices are often hybrid, containing interfaces between the perovskite and metal oxide or organic semiconductor layers. Heterojunctions between two perovskite layers could enable new paradigms in device engineering, but to date, their formation has remained limited due to difficulty in fabricating multilayers and facile ion diffusion across interfaces. Here, sequential solution and vapor processing is used to successfully fabricate perovskite/perovskite heterojunctions comprising three-dimensional APbX3/CH3NH3SnX3 [A = CH(NH2)2, CH3NH3, or Cs; X = I or Br] layers. Heterojunction stability is investigated leading to the identification of two pairings that are stable for >1500 h at room temperature. By probing mixing as a function of composition and grain size, we propose general design rules for the realization of stable perovskite/perovskite heterojunctions.