Regioisomeric Halogenation Tunes Excited Charge Dynamics in DJ-Phase Halide Perovskites: Insights from Interpretable Machine Learning

Spacer cation engineering controls charge transport in Dion–Jacobson (DJ) phase layered halide perovskites (LHPs), yet the impact of regioisomeric spacer functionalization on excited-state dynamics remains largely unexplored. Here, we employ nonadiabatic molecular dynamics, time-domain density functional theory, and interpretable machine learning to uncover the impact of regioisomeric fluorine functionalization on controlling photo-generated carrier dynamics in DJ-phase perovskites. The study reveals that the intrinsic dipole moment of the difluorinated spacer governs interspacer dynamics and inorganic–organic interfacial interactions. The magnitude and direction of the molecular dipole inside the interlayer space dramatically extend carrier lifetime in LHPs, including a 3-fold increase in hot electron cooling time. SHapley Additive exPlanations help understand subtle heterointerfacial features, including layer spacing, axial Pb–I bonds, and interfacial angles that govern bandgap fluctuations and electronic transition probabilities. Our work establishes regiospecific functionalization as a robust design strategy to boost the optoelectronics in DJ-phase perovskites.