Enhancing photostability of 2D Ruddlesden-Popper perovskite via molecular acceptor passivation of metallic lead defects

Two-dimensional (2D) Ruddlesden-Popper (RP) perovskites hold great potential for novel optoelectronic applications. However, their unconventional optoelectronic properties are often compromised by a vulnerability to light irradiation, which leads to the formation of metallic Pb (Pb-0) defects. This study investigates the passivation mechanism of these Pb-0 defects in phenylethylammonium lead iodide (PEA(2)PbI(4)) using a strong molecular acceptor, 2,2 '-(perfluoronaphthalene-2, 6-diylidene) dimalononitrile (F6-TCNNQ). In situ x-ray photoelectron spectroscopy results demonstrate that F6-TCNNQ effectively removes the light-induced Pb-0 states, leading to the recovery of photoluminescence intensity in photodegraded PEA(2)PbI(4) samples and significantly improving the photostability of pristine PEA(2)PbI(4). F6-TCNNQ protects the terrace edge of PEA(2)PbI(4), which is the site of initial degradation, as evidenced by atomic force microscopy and scanning electron microscopy analyses. In situ ultraviolet photoelectron spectroscopy measurements confirm substantial electron transfer from Pb-0 to F6-TCNNQ, causing the oxidation of Pb-0 to Pb2+. Furthermore, the staggered energy level alignment prevents electron transfer from the valence band maximum of PEA(2)PbI(4) to the lowest unoccupied molecular orbital of F6-TCNNQ, thereby preserving the pristine electronic structure of PEA(2)PbI(4). These findings provide new insights into defect passivation in 2D RP perovskites and offer a design strategy for highly stable optoelectronic devices.