Bipolaron hopping conduction in vacancy-ordered Cs₂PtI₆ perovskites.

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Vacancy-ordered perovskites like Cs2PtI6 show promise for solar energy applications due to their efficiency and stability.
• However, the charge conduction and relaxation mechanisms in Cs2PtI6 are not fully understood, limiting further development.

Purpose of the Study:

• To investigate the charge conduction and relaxation mechanisms in Cs2PtI6.
• To elucidate the role of structural features and electronic states in the material's performance.

Main Methods:

• Temperature-dependent impedance spectroscopy to analyze conductivity and activation energy.
• Temperature-dependent Raman spectroscopy to probe vibrational modes and their relation to charge transport.
• X-ray photoemission spectroscopy (XPS) to determine the oxidation states of platinum.

Main Results:

• Activation energy analysis and Raman spectroscopy indicate polaronic charge conduction.
• AC conductivity data suggests correlated barrier hopping as the dominant charge transport mechanism.
• XPS confirmed mixed Pt oxidation states (Pt2+ and Pt4+), with phonon-assisted charge transfer supporting bipolaron redox-mediated conduction.

Conclusions:

• The charge transport in Cs2PtI6 is primarily governed by polaronic conduction and correlated barrier hopping, influenced by isolated octahedra acting as barriers.
• Enhanced conductivity at higher temperatures results from increased carrier energy to overcome barriers and faster hopping rates.
• The findings provide crucial insights into the charge transport dynamics of Cs2PtI6, paving the way for optimized photovoltaic and photoelectrochemical devices.