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 MAPbI₃ (where MA⁺ is CH₃NH₃ ⁺) 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 Pb²⁺ sites. This e-field-driven ion migration and self-filling of iodide vacancies in MAPbI₃ 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.