A Dendrite-Structured RbX (X=Br, I) Interlayer for CsPbI₂ Br Perovskite Solar Cells with Over 15 % Stabilized Efficiency

Interface engineering has shown great potential to improve the photovoltaic performance and long-term stability of perovskite solar cells. Herein, RbX (X=Br, I) materials were developed as the interfacial modifiers for CsPbI₂ Br solar cells that realized power conversion efficiencies (PCE) over 15 % with a high open-circuit voltage (V_OC ) of 1.27 V. The RbX interlayer having a dendrite-shaped structure could optimize the surface wetting behavior of TiO₂ films and thus enabled formation of high-quality perovskite films. More importantly, RbX could better align the devices' energy levels and passivate surface defects because of its large bandgap. The PCE of a CsPbI₂ Br device with RbX interlayer remained 87 % of its initial efficiency for 800 h in ambient atmosphere.