LAUSR

Organic‐inorganic hybrid perovskite solar cells (PSCs) have rapidly developed over the past decade and have achieved the latest certified power conversion efficiency (PCE) up to 25.5%. However, unsatisfactory long‐term operational stability for these hybrid PSCs remains a huge obstacle to further development and commercialization. Herein, a unique hetero‐structured CsPbI3/CaF2 perovskite/fluoride nanocomposites (PFNCs) is fabricated via a newly developed facile two‐step hetero‐epitaxial growth strategy to deliver efficient and ultra‐stable PSCs. After being incorporated into the crystal lattice of α‐phase CsPbI3 perovskite, the cubic‐phase CaF2 in the resultant CsPbI3/CaF2 PFNCs can not only passivate the intrinsic defects of CsPbI3 perovskite itself but also effectively suppress the notorious ion migration in hybrid perovskite Cs0.05FA0.81MA0.14PbI2.55Br0.45 (CsFAMA) thin‐films of PSCs. As such, the CsFAMA PSC devices based on CsPbI3/CaF2‐deposited perovskite thin‐film achieve a mean PCE of 20.45%, in sharp contrast to 19.33% of the control devices without deposition. Specifically, the CsPbI3/CaF2‐deposited PSC retains 85% of its original PCE after 1000 h continuous operation at the maximum power point under AM 1.5G solar light, far better than those of the control and CsPbI3‐deposited PSCs with a device T85 lifetime of 315 and 125 h, respectively.