Roles of Organic Ligands in Ambient Stability of Layered Halide Perovskites

Abstract

The combination of organic ligands and inorganic Pb−I frameworks in layered perovskites has bestowed upon them high structural tunability and stability, while their microscopic degradation mechanism remains unclear. Here, we found the key role of ligands in intrinsic structural stability and the consequent morphological evolution in layered perovskites during long-term ambient aging based on (GA)(MA) n Pb n I 3n+1 (GA = guanidinium, <n> = 4) and (BDA)(MA) n−1 Pb n I 3n+1 (BDA = 1,4-butanediammonium, < n > = 4) perovskites. The BDA-based perovskites have a low intrinsic stability due to high crystal formation energy (ΔH), which are prone to hydration during ambient aging. We overserved changed crystal orientation from perpendicular to parallel, a delayed charge populating time from <1 ps to >50 ps, an inhibited carrier transfer kinetics between quantum wells, an increase of 0.9 μs of charge carrier transport time and a decrease of 1.2 μs of charge carrier lifetime in the BDA-based film during ambient aging, which accounts for a large power-conversion efficiency (PCE) loss (14.2% vs 11.2%). By contrast, the GA ligand increases the intrinsic structural stability of perovskites, which not only yields an initial PCE as high as 20.0% but also helps retain excellent optoelectronic properties during aging. Therefore, only a slight PCE loss (20.0% vs 19.1%) was observed. Our work reveals the key role of organic−inorganic interaction affecting the intrinsic structural stability and optoelectronic properties, and provides a theoretical basis for the future design of stable and efficient optoelectronic devices.

Stabilizing α-Phase FAPbI3 Perovskite Induced by an Ordered Solvated Quasi-Crystalline PbI2

“…Although such a high PCE seems to be sufficient for commercialization, stability should be guaranteed for practical applications. As far as we are concerned, the undesirable stress and defect formed simultaneously during the crystallization of perovskite film can induce lattice distortions, which further facilitate ion migration and structural instability and eventually degrade device performance and stability. − …”