Single Crystal Seed Induced Epitaxial Growth Stabilizes α-FAPbI 3 in Perovskite Solar Cells.

FAPbI 3 stands out as an ideal candidate for the photoabsorbing layer of perovskite solar cells (PSCs), showcasing outstanding photovoltaic properties. Nonetheless, stabilizing photoactive α-FAPbI 3 remains a challenge due to the lower formation energy of the competitive photoinactive δ-phase. In this study, we employ tetraethylphosphonium lead tribromide (TEPPbBr 3 ) single crystals as templates for the epitaxial growth of PbI 2 . The strategic use of TEPPbBr 3 optimizes the evolution of intermediates and the crystallization kinetics of perovskites, leading to high-quality and phase-stable α-FAPbI 3 films. The TEPPbBr 3 -modified perovskite exhibits optimized carrier dynamics, yielding a champion efficiency of 25.13% with a small voltage loss of 0.34 V. Furthermore, the target device maintains 90% of its initial PCE under maximum power point (MPP) tracking over 1000 h. This work establishes a promising pathway through single crystal seed based epitaxial growth for achieving satisfactory crystallization regulation and phase stabilization of α-FAPbI 3 perovskites toward high-efficiency and stable PSCs.