Exciton‐Photon Critical Coupling in Size‐Tailored Quantum Dots Enables >22% Efficient and Stable Inverted CsPbI 3 Solar Cells

ABSTRACT All‐inorganic CsPbI 3 inverted perovskite solar cells (PSCs) suffer from severe nonradiative recombination and interfacial defects, which limit their efficiency and stability. To address this, we developed an interface engineering strategy based on CsPbBr 3 quantum dots anchored in pore‐size‐tuned mesoporous silica nanoparticles (CPBQDs@MSNs), constructing a CsPbI 3 /CPBQDs@MSNs heterojunction. Notably, CPBQDs@M‐MSNs (∼8 nm) match the exciton Bohr radius of CsPbBr 3 (∼7 nm), enabling optimal exciton‐photon critical coupling. This coupling strongly suppresses nonradiative recombination and thermal activation of defects, leading to superior fluorescence stability over a broad temperature range. The CPBQDs@MSNs treatment further enhances crystallinity, reduces grain boundary defects, and optimizes interfacial energy level alignment, thereby facilitating efficient charge‐transport. Consequently, the inverted CsPbI 3 PSCs achieve a remarkable power conversion efficiency (PCE) of 22.15%, the highest value for such devices, along with a record open‐circuit voltage ( V OC ) of 1.28 V. The devices exhibit excellent stability, retaining 93.16% of their initial PCE after 1300 h in ambient air and 98.14% after 1000 h of continuous illumination. This work highlights the crucial role of size‐controlled QDs in interfacial engineering and offers a promising strategy for developing high‐performance and stable perovskite optoelectronic devices.