Stability of the Halide Double Perovskite Cs₂AgInBr₆

Area of Science:

• Materials Science
• Solid-State Chemistry
• Photovoltaics

Background:

• Lead-free halide perovskites are crucial for next-generation solar cells.
• Cesium silver indium bromide (Cs₂AgInBr₆) is theoretically predicted to be a stable material with a direct band gap.
• Previous synthesis reports for Cs₂AgInBr₆ are limited.

Purpose of the Study:

• To synthesize Cs₂AgInBr₆ thin films using thermal evaporation.
• To investigate the stability and properties of Cs₂AgInBr₆ thin films.
• To assess the potential of Cs₂AgInBr₆ for device applications.

Main Methods:

• Thin film synthesis via thermal evaporation of CsBr, AgBr, and InBr₃.
• Annealing of synthesized films at temperatures ranging from 130 °C to 250 °C.
• Characterization of film stability and optical properties, including band gap determination.

Main Results:

• Cs₂AgInBr₆ thin films were successfully formed through thermal evaporation and annealing.
• The material exhibits apparent stability within the 130 °C to 250 °C annealing range.
• However, Cs₂AgInBr₆ thin films are intrinsically thermodynamically unstable at room temperature, decomposing into other phases (Cs₂AgBr₃, Cs₃In₂Br₉, AgBr, InBr₃).
• This instability was observed consistently, irrespective of illumination, film thickness, or annealing conditions.
• Optical absorption measurements suggest a direct band gap of 1.57 ± 0.1 eV for Cs₂AgInBr₆.

Conclusions:

• While Cs₂AgInBr₆ can be synthesized and exhibits a potentially useful band gap, its intrinsic thermodynamic instability at room temperature prevents its practical application in devices.
• Further research is needed to stabilize this material or explore alternative lead-free perovskites with improved stability.
• The findings highlight the importance of thermodynamic stability assessments for novel photovoltaic materials.