Halogen Surface Terminations in Ti 3 C 2 MXenes for Interface Engineering in Perovskite Solar Cells

ABSTRACT Halogen surface functionalization has emerged as a promising strategy to modulate MXene properties. However, most reported MXenes exhibit heterogeneous surface terminations (), hindering the establishment of clear correlations between structure and electronic properties. Here, delaminated MXenes with controlled –Cl and –Br terminations are investigated to elucidate the relationship between surface chemistry and the electronic and optical response. To explore their impact on optoelectronic devices, the MXenes are employed as dopants in an IT‐4F interfacial layer positioned between the electron transport layer and the perovskite absorber in n‐i‐p architectures. A combined theoretical and experimental approach is used to investigate the role of halogen terminations in modulating MXene and interfacial layer properties. While limited effects are observed in planar devices, mesoscopic solar cells based on FTO/c‐/m‐//PEAI/PTAA/Au exhibit improved performance upon incorporation of 1 vol% MXene in IT‐4F, with Br‐terminated yielding the highest average power conversion efficiency (15.44 0.21%) and a champion efficiency of 17.06%. These findings highlight the influence of halogen surface terminations on MXene properties and device performance.