Bipolaron hopping conduction in vacancy-ordered Cs2PtI6 perovskites

Abstract

Among vacancy-ordered perovskites, Cs₂PtI₆ exhibits remarkable efficiency and stability, making it a promising material for photovoltaic and photoelectrochemical applications. However, further advancements require a comprehensive understanding of its charge conduction and relaxation mechanisms, which remain insufficiently explored. This study investigates these mechanisms through temperature-dependent impedance and Raman spectroscopic techniques. Activation energy analysis from conductivity data and temperature-dependent Raman spectroscopy suggests polaronic type conduction. The frequency exponent trend from AC conductivity reveals that correlated barrier hopping is the primary charge conduction mechanism, with the isolated octahedra in the structure acting as barriers for polaron hopping. Enhanced conductivity at higher temperatures is attributed to energy gained by carriers to overcome potential barriers for conduction and increased hopping rates. X-ray photoemission spectroscopy reveals the presence of mixed Pt oxidation states (Pt²⁺ and Pt⁴⁺), and the phonon-assisted charge transfer between them supports bipolaron redox-mediated conduction.