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

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 (FASnI3). EDA0.01FA0.98SnI3:Ge-based photodiodes demonstrate a significantly improved specific detectivity (1.6 x 1012 Jones at -0.1 V), cut-off frequency (6.6 x 105 Hz), response speed (0.53 mu s), and signal-to-noise ratio (45 dB) compared with control devices. The superior performance is attributed to the stronger Ge & horbar;I bond, the passivation of Sn2+ and I- vacancies by smaller Ge2+ 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. Germanium- and ethylenediamine-added lead-free tin-based perovskite photodetector demonstrates one of the best photodetection and air stability, as certified by the national institute. There are five beneficial effects induced by the Ge and ethylenediamine additions: Ge i) forms stronger bonding, ii) fills vacancies, and iii) constructs GeO protective layer; ethylenediamine iv) promotes 3D structure, and v) elevates the conduction level. image