Combining DFT Calculations and Clustering Techniques to Screen Organic Monovalent Cations for Applications in Halide...

Surface passivation is widely used to improve the operational stability and efficiency of hybrid perovskite photovoltaics; however, the selection of passivation agents remains largely empirical. We present a computational framework that combines high-throughput density functional theory calculations with unsupervised clustering to analyze the adsorption of 134 organic cations, applied as post-treatment interfacial passivators, on zero-dimensional Cs₄[PbI₆] perovskite fragments. We find that passivation is not captured by a single descriptor (e.g., cation electron affinity or molecular geometry), but instead reflects a balance between interfacial electronic stabilization and structural deformation of the organic backbone. Rigid, highly π-conjugated cations exhibit large deformation penalties (up to 1.12 eV), which offset favorable interfacial interactions and weaken net adsorption. In contrast, bulky coordination-saturated cations are stabilized by dispersion-driven hydrophobic encapsulation and exhibit favorable deformation energies (down to -1.85 eV). Flexible primary amines and geometrically unhindered cations enable anchoring with near-zero deformation costs. Electronic-structure analysis indicates two regimes: conjugated molecules introduce low-lying states within the perovskite band gap (Type II alignment), which may act as charge-trapping states, whereas saturated backbones behave as wide-gap insulators (Type I alignment) that preserve the optoelectronic structure of the perovskite. Overall, the screening suggests that effective candidates should combine conformational flexibility (to limit deformation penalties) with electronic saturation (to reduce Type II trap formation) and thereby inform the design of stable perovskite interfaces for optoelectronic devices.