Passivating Charged Defects with 1,6-Hexamethylenediamine to Realize Efficient and Stable Tin-Based Perovskite Solar Cells

An organic cationic salt, hexamethylenediamine diiodide (HDADI), is introduced into formamidinium tin iodide (FASnI3) perovskite solar cells (PSCs) by consideration of amino group passivation of HDA2+ to iodide of SnI64- and assisted links of amino groups at both ends of HDA2+ to the perovskite unit cell to form the Dion-Jacobson (DJ) layered two-dimensional (2D) perovskite. X-ray diffraction and grazing-incidence wide-angle X-ray scattering characteristics exclude the formation of the DJ layered 2D perovskite. A decent power conversion efficiency (PCE) and stability are derived from the high-quality perovskite films with large coverage, high crystallinity, and disappeared pinholes as well as increased radiative recombination and a prolonged carrier lifetime, which are associated with the interaction of NH3+ and SnI64- octahedra via a hydrogen bond. The interaction not only neutralizes charged defects or dangling bonds of perovskites but also forms a shield to retard the oxidation of Sn2+ to Sn4+ and reduce Sn vacancies. Applications of the HDADI-treated FASnI3 films into PSCs acquire a champion PCE of 7.6% and an outstanding long-term stability of over 550 h to retain 80% of the initial efficiency in a glovebox with a N2 environment. This work may guide the design of highly stable and efficient Sn-based PSCs.