Photoinduced Vibrations Drive Ultrafast Structural Distortion in Lead Halide Perovskite

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Organic-inorganic perovskites are crucial for optoelectronics, with performance linked to microscopic structural dynamics post-photoexcitation.
• Understanding the interplay between organic cations and the inorganic sublattice is key to optimizing perovskite material properties and device efficiency.

Purpose of the Study:

• To investigate the structural dynamics of methylammonium (MA) lead iodide perovskite after photoexcitation using advanced spectroscopic techniques.
• To reveal the coupled vibrational motions between the organic cation and inorganic sublattice and their role in polaron formation.

Main Methods:

• Ultrafast heterodyne-detected two-dimensional (2D) electronic spectroscopy to probe impulsively excited vibrational modes.
• Vibrational analysis and wavelet analysis to monitor time-evolved motions and coherences.
• Configuration interaction singles (CIS) calculations for theoretical support and mechanistic insights.

Main Results:

• Experimental observation of coupled librational motion of the MA cation and vibrational coherences of the inorganic sublattice within 300 fs.
• Theoretical calculations confirm the coherent generation of these motions and highlight anharmonic interactions.
• Prediction of photoinduced vibrational coherence transfer from MA cation to inorganic sublattice, leading to long-lived polaronic states.

Conclusions:

• The study elucidates the dynamic interplay between organic cations and inorganic sublattices in perovskites during photoexcitation.
• Coherent vibrational dynamics play a critical role in the formation of polaronic states.
• Findings offer insights for designing next-generation perovskite solar cell materials with improved performance.