Additive‐Free Crystallization Modulation for Efficient Perovskite Solar Cells by a Transverse Pulsed Electric Field

Controlling the migration and spatial distribution of ionic constituents during perovskite growth represents a powerful approach to modulate the crystallization process and achieve optimal film morphology. However, the well‐controlled regulation of specific ionic species and its consequences for oriented growth and defect suppression have received limited attention. Herein, a transverse pulsed electric field (e‐field) is introduced to guide the directional migration of perovskite constituents, offering an alternative to crystallization control that is typically achieved with chemical additives. The MAPbI 3 (where MA + is CH 3 NH 3 + ) films exhibit a lateral gradient in iodine species distribution, which correlates with improved crystal orientation, decreased iodide loss, and reduced formation of iodide vacancies. The e‐field‐assisted thermal annealing enables the facile migration of unanchored iodides in perovskite films, allowing mobile I − ions to fill vacancies and passivate undercoordinated Pb 2+ sites. This e‐field‐driven ion migration and self‐filling of iodide vacancies in MAPbI 3 could mitigate iodine‐related defects caused by iodine loss and lower non‐radiative recombination, leading to perovskite solar cells with improved efficiency and stability. Furthermore, this strategy is adaptable to the perovskites with mixed A‐site cations and halides, delivering an efficiency of over 24%. These results provide new insights into defect self‐passivation mediated with controlled e‐field for high‐performance devices.