Fabricating Solid‐Solution‐Type Perovskite/Fluoride Nanocomposites Through Sublattice Interlocking for High‐Performance Photovoltaics

All‐inorganic α‐phase CsPbI3 perovskite with a suitable bandgap and superb optoelectronic properties is transforming the landscape of perovskite photovoltaics, but its long‐term lability associated with “soft” ionic lattice still imposes a great challenge for practical applications. Herein, a unique solid‐solution fluorination strategy is proposed to deliver an “ideal” perovskite matrix of α‐phase CsPbI3 abundant with F ions through interlocking the soft lattice of CsPbI3 with cubic‐phase CsF·3/2HF. Such a sublattice interlocking can not only stabilize the soft lattice of α‐phase CsPbI3 perovskite nanocrystals but also passivate their notorious surface defects, thereby producing a “rigid” solid‐solution‐type perovskite/fluoride CsPbI3/CsF (termed as CsPbI3:F) nanocomposite with excellent long‐term stability and a near‐unity photoluminescence efficiency. Of particular note is that these CsPbI3:F nanocomposites can work well as effective grain boundary anchors to significantly improve the photovoltaic performance of perovskite solar cells because of their F‐rich perovskite lattice, achieving a T80 stability of 1500 h under continuous maximum power point tracking and AM 1.5G illumination without the need for encapsulation. This work paves a new way to deliver perovskite materials with desirable properties for photovoltaics. A novel solid‐solution‐type perovskite/fluoride nanocomposite, CsPbI3/CsF (referred to as CsPbI3:F), is constructed by interlocking the “soft” lattice of CsPbI3 with CsF·3/2HF for fabricating high‐performance perovskite solar cells (PSCs). The PSC device, based on a CsPbI3:F‐deposited Cs0.05FA0.81MA0.14PbI2.55Br0.45 film, maintains 80% of its initial power conversion efficiency after continuous operation for 1500 h at maximum power point tracking under AM 1.5G illumination.