Engineered Electronic Structure and Carrier Dynamics in Emerging Cs₂AgNa_1-FeCl₆ Perovskite Single Crystals

Area of Science:

• Materials Science
• Solid-State Chemistry
• Photovoltaics

Background:

• Lead-free double perovskites offer compositional flexibility and electronic diversity.
• Cs2AgxNa1-xFeCl6 perovskites are a new class with high thermal stability.

Purpose of the Study:

• To synthesize and characterize novel Cs2AgxNa1-xFeCl6 perovskite single crystals.
• To investigate the effect of B-site cation substitution on crystallographic and electronic properties.
• To explore their potential for optoelectronic and photovoltaic applications.

Main Methods:

• Hydrothermal crystal growth.
• Composition engineering via B-site cation substitution (Ag+ and Na+).
• Ultrafast transient absorption spectroscopy (TAS).
• Electron mobility measurements.

Main Results:

• Synthesized Cs2AgxNa1-xFeCl6 single crystals with tunable band structure and near-infrared absorption (~800 nm).
• TAS revealed significantly longer excited-state absorption decay times with increasing Ag concentration (up to 2450 ps).
• Charge carrier diffusion length increased from 3.7 to 311 nm, and electron mobility enhanced ~15 times (to 15.3 cm2 V-1 s-1).

Conclusions:

• Partial substitution of [NaCl6]5- by [AgCl6]5- shrinks the primitive cell and enhances orbital coupling.
• Silver incorporation effectively improves electron mobility and charge carrier diffusion.
• These lead-free double perovskites are promising candidates for optoelectronic and photovoltaic devices.