A First-Principles Study of Doped Graphene Clusters for Passivating Tin-Based Perovskite Solar Cells

Tin-based perovskites are promising light absorbers for perovskite solar cells (PSCs) due to their reduced toxicity compared to lead-based counterparts. However, stabilizing the Sn²⁺ oxidation state remains critical for achieving high device lifetime. While two-dimensional graphene has been proposed as a passivating layer, our density functional theory (DFT) calculations reveal its weak interaction with the perovskite surface, limiting its practical application. To overcome this challenge, we systematically investigated five doped graphene clusters, including graphitic boron (B), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S). Our analysis identifies the highest occupied molecular orbital (HOMO) energy and HOMO-LUMO (lowest unoccupied molecular orbital) gap as complementary descriptors of interfacial charge redistribution. Among the studied systems, O-doped graphene shows the most promising combination of electronic and adsorption properties, with C atoms adjacent to O dopants forming stable bonds with surface Sn. The associated charge redistribution is consistent with a potential role in stabilising surface Sn. These findings provide theoretical guidance for designing doped graphene-based passivators for tin-based PSCs.