Spontaneous Ion Migration via Mechanochemical Ultrasonication in Mixed Halide Perovskite Phase Formation: Experimental and Theoretical Insights

We present a simple yet powerful synthesis process to prepare compound-phase perovskite nanoparticles (MAPbX(3-n)Y(n); MA = CH3NH3+ and X/Y = I, Br, or CI). This is achieved by mixing two pure-phase perovskites (MAPbX(3) and MAPbY(3)) by using ultrasonic vibration as a mechanochemical excitation. Unlike conventional methods, this procedure does not require any effort in designing a reaction or choosing any particular precursor. X-ray diffraction and TEM studies confirm compound-phase formation in all possible stoichiometries. The origin behind ultrasonic mixing lies in the generation of mechanical stress and high temperature arising from acoustic cavitation during reaction. Long-term experimental stability of the compound-phase is comprehended theoretically by simulating the temperature-dependent Gibbs free energy. Negative mixing entropy plays a crucial role during the synthesis which leads to better stabilization of the compound-phase perovskite over the pure-phase. The ease of synthesis and remarkable phase stability make this process effective and less cumbersome for perovskite nanoparticle synthesis.

Automated summary

A simple synthesis process for compound-phase perovskite nanoparticles was introduced, which involves mixing two pure-phase perovskites using ultrasonic vibration. The method eliminates the need for designing a reaction or selecting specific precursors, providing better stability and synthesis efficiency.