Pb-free halide double perovskites (HDPs) are proposed as potential candidates for various optoelectronic applications to replace the mainstream hybrid organic-inorganic halide perovskites, e.g., CH₃NH₃PbI₃. While it is known that ion diffusion is a critical problem to affect the structural and electronic stability of CH₃NH₃PbI₃, the mechanism of ion diffusions in HDPs is still unclear and highly desired to be revealed. In this study, taking Cs₂AgInX₆ (X = Cl, Br) HDPs as prototypes, for the first time we suggest that the fast ion diffusion of the dominant defects may play an important role in the performance stability of HDPs. Importantly, we find that the Ag_i⁺ diffusion in a multi-ion concerted fashion has a much faster diffusion rate, compared to the V_Ag⁻ and V_X⁺ diffusion in a single-ion fashion. It is revealed that HDPs exhibit quite different diffusion properties from CH₃NH₃PbI₃. Furthermore, we demonstrate that the diffusion rate of Ag_i⁺ in HDPs can be effectively suppressed by applying an epitaxial strain, which opens a promising way to enhance the performance stability of perovskite materials for various device applications.

无铅卤化物双钙钛矿（HDPs）被提议作为各种光电应用的潜在候选者，以取代主流的杂化有机-无机卤化物钙钛矿，例如CH ₃ NH ₃ PbI ₃。虽然已知离子扩散是影响CH ₃ NH ₃ PbI ₃的结构和电子稳定性的关键问题，但HDP中离子扩散的机制仍不清楚，并且非常需要揭示。在本研究中，采用Cs ₂ AgInX ₆（X = Cl，Br）HDPs作为原型，我们首次建议主要缺陷的快速离子扩散可能在HDPs的性能稳定性中起重要作用。重要的是，我们发现，银_我⁺在多离子协调的方式扩散具有更快的扩散速率，相比于V_银^-和V _X ⁺在一个单一的离子扩散的方式。结果表明，HDP与CH ₃ NH ₃ PbI _3的扩散特性完全不同。此外，我们证明了Ag _i ⁺的扩散速率 通过施加外延应变可以有效地抑制HDP中的钙钛矿，这为增强钙钛矿材料在各种器件应用中的性能稳定性开辟了一种有希望的途径。