Lattice Coherency‐Driven (111)‐Oriented Wide Bandgap Perovskite Films

ABSTRACT Perovskite solar cells (PSCs) have exhibited astonishing progress in power conversion efficiency (PCE) along with a remarkable improvement in long‐term stability. A precise control on crystal growth, however, still remains challenging, particularly for poly‐crystalline perovskite films based on solution‐ and low temperature‐processing. Here in, we introduce a simple but effective strategy to regulate the crystallographic orientation of wide bandgap perovskite films (FA 0.79 MA 0.12 Cs 0.09 Pb(I 0.85 Br 0.15 ) 3 ; FA = formamidinium, MA = methylammonium) by utilizing lattice coherency with seed template, where MAPbBr X Cl 3−X not only serves as a kinetic controller for retarding crystal growth but also performs as a seed template to reshape the thermodynamic energy cost for regulating crystal orientation along face‐up (111) array by offering enthalpy‐driven reduced Gibbs free energy change. Consequently, perovskite films grown with the aid of a seed template exhibit outstanding crystallinity with the preferential orientation, while a weak crystallinity with a relatively random orientation is observed from the control sample. Noticeably, devices employing the (111)‐oriented ordered structure, in spite of its unfavorable charge extraction, eventually result in competitive PCEs and superior long‐term stability at the elevated temperature to those of (001)‐oriented ones, emphasizing the importance of a highly ordered lattice with facet control in governing the device performance.