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

All-inorganic alpha-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 alpha-phase CsPbI3 abundant with F ions through interlocking the soft lattice of CsPbI3 with cubic-phase CsF3/2HF. Such a sublattice interlocking can not only stabilize the soft lattice of alpha-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 T-80 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.