Synergistic Treatments of Bulk and Buried Surface in Tin‐Lead Binary Perovskite for Efficient Near‐Infrared Photodetectors

Abstract Tin‐lead binary perovskites, with their low bandgap and high absorption coefficient, hold great potential for application in near‐infrared (NIR) photodetectors. However, uncontrolled crystallization and a high defect density at the interface, particularly at the buried interface, significantly hinder their performance enhancement. To address this challenge, this work incorporated the quaternary ammonium salt tetrabutylammonium iodide (TBAI) into the precursor solution. TBAPbI ₃ with low formation energy accumulates rapidly at the bottom interface, templates the growth of 3D perovskite films, and effectively reduces the bulk defect density. Furthermore, TBAPbI ₃ at the bottom also passivates the FA ⁺ vacancy defect. These synergistic treatments effectively passivate both bulk and buried surface defects of varying nature, thereby limiting the ingress of oxygen into the film and reducing the oxidation of Sn ²⁺ . The resulting photodetectors exhibited outstanding performance, including a high responsivity (0.53 A W ⁻¹ at 860 nm), an excellent detectivity (4.6 × 10 ¹² Jones), and an ultrafast response speed (93.2 ns), as well as enhanced environmental stability. Leveraging its exceptional photoelectric performance, a flexible NIR photodetector is integrated into a wearable reflective oximetry detection system, achieving accurate and non‐invasive assessment of heart rate and blood oxygen saturation. These results highlight the promising potential of tin‐lead perovskites for health monitoring applications.