Controlling Phase Transition Dynamics in Laser-Printed Perovskite Films via Additive-Driven Strain Engineering

The structural phase transitions in hybrid perovskites are critical to their performance and stability, but controlling them remains a significant challenge. Here, we demonstrate that the dynamics of the low-temperature tetragonal-to-orthorhombic phase transition in laser-printed MAPbI3 films can be controlled by tailoring additive chemistry. We show that the choice of charge control agent (CCA) directly impacts the intrinsic defect and strain landscape of the resulting film: an ionic CCA promotes a low-strain lattice that facilitates the phase transition. In contrast, a molecular CCA induces a high-strain, defect-rich lattice, which creates a high kinetic barrier that suppresses the transition and effectively “pins” the tetragonal phase. This work establishes a strategy to engineer strain and manage phase behavior in perovskite films, demonstrating that the ability to “lock” or “enable” a specific crystal phase by selecting additives provides a pathway to mitigate degradation and engineer stable, high-performance perovskite devices.