Effective Dual Cation Release in Quasi‐2D Perovskites for Ultrafast UV Light‐Powered Imaging

Abstract Ruddlesden‐Popper quasi‐2D perovskites represent robust candidates for optoelectronic applications, achieving a delicate balance between outstanding photoresponse and stability. However, mitigating the internal defects in polycrystalline films remains challenging, and their optoelectronic performances still lag behind that of their 3D counterparts. This work highlights the profound impact of defect passivation at the buried interface and grain boundaries through a dual‐cation‐release strategy. Cations released from the pre‐deposited inorganic iodide buffer layer effectively repair deep‐level defects by inducing low‐dimensional phase reconstruction and interacting with undercoordinated ions. The resulting quasi‐2D perovskite polycrystalline films feature large grain size (>2 µm) and minimum surface roughness, along with alleviated out‐of‐plane residual tensile strain, which is beneficial for inhibiting the initiation and propagation of cracks. The fabricated photodetector demonstrates drastically improved self‐powered photoresponse capability, with maximum responsivity up to 0.41 A W −1 at 430 nm and an ultrafast response speed of 161 ns / 1.91 µs. Moreover, this strategy is compatible with the photolithography‐assisted hydrophobic‐hydrophilic patterning process for fabricating pixelated photodetector arrays, which enables high‐sensitivity imaging. This study presents a feasible defect passivation approach in quasi‐2D perovskites, thereby providing insights into the fabrication of high‐performance optoelectronic devices.