Collaborative Management of Light‐Absorbing Supplementation and Defect Passivation Based on Green‐Emitting ((CH₃)₄N)₂(C₂H₅)₄N·MnBr₄ Single Crystals for Efficient and Stable Inverted Perovskite Solar Cells

In conventional p–i–n inverted perovskite solar cells (PSCs), there exists considerable energy loss due to both unsatisfactory light path design and trap‐induced interfacial defects. The sunlight is absorbed competitively by conductive oxide substrates and hole transport material in front of the perovskite layer, while the opaque metal back electrode also prevents light penetration. Worse yet, there is severe nonradiative charge recombination caused by defects between the perovskite layer and the electron transport material. To tackle the above two issues, a new green‐emitting material ((CH₃)₄ N)₂(C₂H₅)₄N·MnBr₄ is synthesized and introduced in/on the perovskite layer to achieve both defect passivation and light complementation. The green luminescence of this single crystal at the interface is found to provide secondary light absorption, as evidenced by a remarkable promotion of short‐circuit current density. It is also found that the excess PbI₂ on the surface of perovskite can be effectively removed, and as the interfacial additive, ((CH₃)₄ N)₂(C₂H₅)₄ N·MnBr₄ inhibits trap‐assisted recombination losses, which provides favorable energy‐level alignment and extends charge carrier lifetime. As a result, the champion PCE (21.23%) of the target‐treated ((CH₃)₄ N)₂(C₂H₅)₄ N·MnBr₄ device exceeds that 19.5% of the pristine‐without ((CH₃)₄ N)₂(C₂H₅)₄ N·MnBr₄ device. This work provides an effective interfacial strategy for high‐performance and stable inverted PSCs.