Modulating Janus Effect of Cations to Control Electronic Symmetry and Hole Mobility in Spiro-OMeTAD for Perovskite Solar Cells

Li-TFSI-doped Spiro-OMeTAD (Spiro) remains the benchmark hole transport material in perovskite solar cells (PSCs). The success of Li-TFSI doping has reinforced the prevailing notion that raising the oxidation level (OL) of Spiro proportionally enhances its conductivity, which relies on both hole concentration and mobility. While the role of hole concentration has been exhaustively explored, the origin of hole mobility enhancement has remained elusive. Here, we unveil the Janus effect of metal cations that decouples Spiro's hole mobility from its OL. Metal cation–π interactions break the molecular symmetry of Spiro, reshaping its electronic structure and directly modulating hole mobility, whereas ion–ion interactions between metal cations and TFSI⁻ anions exclusively govern the OL. By quantifying these orthogonal interactions, we establish a clear structure–property relationship that links electronic symmetry to macroscopic charge transport. This framework provides a rational design paradigm for next-generation, high-mobility hole conductors, applicable to perovskite solar cells and a wide range of optoelectronic materials and devices.