Acoustic Modification of Halide Perovskite Thin Films for Enhanced Crystal Quality and Device Performance

Halide perovskites are championed as defect tolerant PV absorbers, primarily because their shallow trap states do not contribute to non-radiative recombination. However, thin film solution processing techniques, both at lab scale and large-area coatings, often introduce a range of defects - grain boundaries, point defects, CTE mismatch induced strain gradient, octahedral distortion, etc., that impact perovskite phase stability and device performance, thus, necessitating passivation strategies. Herein, we demonstrate the use of acoustic energy as a facile, chemical-free, and potentially scalable approach to enhance the quality of such defect-prone halide perovskite thin films, in the solid state. Building on prior studies of acoustic softening in metals—which connect reduced yield stress to dislocation motion and annihilation under ultrasonic vibrations—we extend this hypothesis to the soft crystal lattice of halide perovskites. In this study, we investigate the mechanistic origins of perovskite film quality improvement when exposed to a high-performance acoustic treatment.
Structural characterization of insonated formamidinium lead iodide (a-FAPbI₃) perovskite films, employing synchrotron-based nano-XRD and GIWAXS techniques, reveal a strain-relieved lattice and a significant reduction in non-perovskite secondary phases. Optoelectronic assessments show that the insonated films exhibit enhanced photoluminescence and an order-of-magnitude boost in external radiative efficiency (ERE), suggesting that the application of acoustic energy effectively diminishes both surface and bulk defects responsible for non-radiative recombination, compared to untreated films.