Ion Diffusion Dynamics and Halogen Mixing at the Heterojunction of Halide Perovskites: Atomistic Insights

Abstract

Hybrid halide perovskites have emerged as a promising class of materials with immense potential for revolutionizing optoelectronic technologies. The exceptionally versatile applications of these materials lie in their tunable band gap and carrier dynamics, achieved through compositional engineering. In mixed hybrid halide perovskites (MHHPs), the homogeneously alloyed anions or their segregated phases, forming precise heterostructures, demonstrate promising photophysics. Nonetheless, an in-depth understanding of the halide interdiffusion perovskite/perovskite heterojunction through interfacial solid-state ion dynamics is mostly missing. Here, we perform first-principles simulations to study the atomistic structure and ion migration processes at the heterojunction between the bromide and iodide phases of lead-based mixed cation perovskites. Due to the anionic size mismatch, the interface remains under structural strain that further depends on the crystal planes of the heterojunction. Moreover, the position of the lattice defect influences the I−Br vacancy formation energetics. The vacancy-assisted ion transports encounter energy barriers that substantially depend on the local structural distortions and strain relaxations along the anion migration pathways. The energetic preference of anion mixing through sequential ion hopping or retainment of a heterojunction strongly relies on the details of the host interfacial plane in this MHHP. Overall, the anion dynamics are directionally anisotropic at these heterojunctions. The study reveals the atomistic solid-state ion diffusion processes in MHHPs and can guide experimental efforts to control anion transport in perovskite/perovskite heterostructures.

Effects of Lattice Compression on Halogen Ion Diffusion Dynamics in Mixed Halide Perovskites

“…Taking a similar approach to previous work, we investigated the change in local structure during ion migration to understand the trends in migration energy barriers . There are two Pb–Pb distances ( d Pb–Pb ) tracked: (1) distance between Pb ions that initially contains the migrating halide ion and finally hosts the newly formed vacancy site ( d Pb–Pb,break ) and (2) separation between the Pb ions that initially have the ion vacancy V X and finally contain the migrated anion ( d Pb–Pb,form ).…”

“…A definitive theory for the cause of such ion segregation is still under debate. However, the key role of anion vacancy-induced anisotropic ion migration in phase segregation has been accepted widely. − The ion migration in halide perovskites is also one of the main reasons for its structural degradation …”

Modification strategies of lead halide perovskite nanocrystals for efficient and stable LEDs

“…Given the significant impact of surface defects on halide ion migration, PNCs resurfacing strategies are promising to block ion migration for stable PNC-LEDs. 48,49 It is known that the surface Cs ions of CsPbX 3 PNCs are usually replaced by protonated amine ligands, which bind to halide atoms via hydrogen bonding. 50 The post- and in situ PNCs resurfacing strategies to boost the binding with halide ions are beneficial for blocking the halide ion migration.…”