Enhanced Photodetection and Air Stability of Lead‐Free Tin Perovskite Photodiodes via Germanium Incorporation and Organic Cation‐Mediated Dimensionality Control

Abstract This work presents the advancement of lead‐free tin perovskite photodiodes in terms of their photodetection and air stability by incorporating germanium (Ge) and ethylenediamine (EDA) to formamidinium tin iodide (FASnI 3 ). EDA 0.01 FA 0.98 SnI 3 :Ge‐based photodiodes demonstrate a significantly improved specific detectivity (1.6 × 10 12 Jones at −0.1 V), cut‐off frequency (6.6 × 10 5 Hz), response speed (0.53 µs), and signal‐to‐noise ratio (45 dB) compared with control devices. The superior performance is attributed to the stronger Ge─I bond, the passivation of Sn 2+ and I – vacancies by smaller Ge 2+ ions, the promotion of a fully 3D perovskite structure, the elevation of the conduction band energy level, and the formation of a protective GeO layer. Various film analyses, including X‐ray photoelectron spectroscopy, UV photoelectron spectroscopy, density functional theory, as well as device testing using time‐of‐flight secondary ion mass spectrometry and voltage‐dependent admittance, support and explain the mechanisms behind the enhancements. Ge‐ and EDA‐incorporated photodiodes exhibit excellent air stability, as evidenced by the time‐dependent ultraviolet visible spectra and the considerably high certified power conversion efficiency without encapsulation in air, demonstrating their potential for practical applications. The obtained photodetection performance is highest among the published lead‐free tin‐based perovskite photodetectors, presenting a monumental progress from the previous report of the same group.