Predictive Structure-Property Design Rules for Quasi-2D Dion-Jacobson Sn-Based Perovskites

Abstract

The $\text{Sn}^{2+}$ instability is the critical bottleneck preventing the widespread implementation of lead-free tin-halide perovskites. While quasi-two-dimensional (Q2D) Dion--Jacobson (DJ) structures offer the leading stability solution, the field's reliance on empirical, application-independent trial-and-error for molecular selection has hampered progress. Here, we move beyond this rut, presenting a high-throughput first-principles study of a set of chemically diverse diammonium spacers to establish a predictive design framework based on fundamental molecular characteristics. We unveil the following fundamental rules: Nonpolar symmetry maximizes thermodynamic stability against decomposition; moderate steric bulk stabilizes polar spacers and promotes efficient packing; short spacers uniquely minimize out-of-plane hole effective masses by reducing electronic confinement; molecular polarity lifts electronic degeneracies near the $\text{CBM}$; and aromatic cores could enhance electronic coupling near the band edges. These universally applicable principles provide the missing foundation for engineering stable, functional 2D DJ perovskites, accelerating their deployment in next-generation optoelectronics.