Metal-Site Chemistry Dominates Carrier Recombination in Layered Halide Perovskites: Insights from Excited-State Dynamics and Interpretable Machine Learning

Abstract

Layered halide perovskites (LHPs) offer a powerful platform to precisely engineer excited-state carrier dynamics and optoelectronic performance via compositional tuning of B-site metals. Here, we contrast prototypical lead-based (BA)2PbBr4 with its double-perovskite analogue (BA)4AgBiBr8 to isolate the role of B-site chemistry in dictating photoactivity in these emerging layered semiconductors. Nonadiabatic molecular dynamics integrated with interpretable machine learning models reveal the detailed impact of time-dependent structural distortions on the instantaneous electronic structures in these LHPs. The alternating [AgBr6]5– and [BiBr6]3– octahedral arrangement in (BA)4AgBiBr8 gives rise to intrinsically stronger structural fluctuations and enhanced electron–phonon coupling, leading to faster nonradiative recombination than that in a more rigid Pb-based framework. Extensive SHapley Additive exPlanations analyses further depict that the thermally driven octahedral distortions in the [AgBiBr8]4+ layers exert the strongest control over excited-state charge dynamics at ambient conditions. The intrinsic structural anisotropy in adjacent Ag/Bi-centered octahedra strengthens electron–phonon coupling, activating nonradiative recombination channels and consequently suppressing the photoluminescence. Our findings establish a mechanistic link among inorganic sublattice composition, structural dynamics, and carrier lifetimes, presenting key design principles to realize high-performing lead-free LHPs for optoelectronics.