CsSnI₃ Quantum Dots as a Multifunctional Interlayer for High‐Efficiency Bilayer Perovskite Solar Cells

Abstract Perovskite solar cells (PSCs) have garnered significant interest due to their potential for high performance at low cost. While single‐junction PSCs have surpassed 26% efficiency, they are nearing their theoretical limits. Introducing dual absorber layers can broaden the spectral absorption range, enhancing performance. This study explores a zero‐dimensional/three‐dimensional (0D/3D) bilayer structure combining three‐dimensional (3D) FAPbI 3 with zero‐dimensional (0D) cesium tin triiodide (CsSnI 3 ) quantum dots (QDs) as an interfacial modification layer. The CsSnI 3 QDs establish a cascade energy level structure, improving charge transfer efficiency at the perovskite‐hole transport layer (HTL) interface. Their narrow bandgap enhances light absorption efficiency, boosting hole extraction and short‐circuit current density. Incorporating CsSnI 3 QDs into PSCs significantly improves the power conversion efficiency from 22.99% to 25.72% compared to 3D perovskite solar cells without the CsSnI 3 QD interlayer. Also, surface‐passivated CsSnI 3 QDs with hydrophobic ligands provide moisture resistance and interfacial passivation, increasing stability. Using perfluorooctanoic acid (PFA) to modify CsSnI 3 QDs further enhances moisture resistance, allowing PSCs to maintain 85% of initial efficiency for over 60 days at 25% relative humidity without encapsulation, demonstrating significant stability improvements. The incorporation of CsSnI 3 QDs in PSCs notably increases power conversion efficiency.