Spontaneous Formation of a Ligand-Based 2D Capping Layer on the Surface of Quasi-2D Perovskite Films

Abstract

Two-dimensional (2D) Ruddlesden–Popper phase perovskites (RPPs) are attracting growing attention for photovoltaic applications due to their enhanced stability compared to three-dimensional (3D) perovskites. The superior tolerance of 2D RPPs films to moisture and oxygen is mainly attributed to the hydrophobic nature of the introduced long-chain spacer cations (ligands). In this work, it is revealed that a thin capping layer, consisting of self-assembled butylammonium ligands, is spontaneously formed on the top surface of a quasi-2D perovskite film prepared by conventional one-step hot casting. Based on morphological and crystallographic analyses of both the top/bottom surfaces and the interior of quasi-2D perovskite films, the formation process of the 2D capping layer and the assembly of RPPs, comprising both large and small slab thickness (large-n, small-n), is elucidated. The vertical orientation of RPPs that is required for sufficient charge transport for 2D perovskite solar cells (PSCs) is further verified. We propose that the surface capping layer is directly responsible for the long-term stability of 2D PSCs. This work provides detailed insight into the microstructure of quasi-2D RPPs films that should assist the development of strategies for unlocking the full potential of 2D perovskites for high-performance PSCs and other solid-state electronic devices.

Quasi‐2D Perovskite with Ligand Engineering to Improve the Stability of Phototransistor Memory with a Floating Gate

“…[ 30,16 ] The low‐n phase scattering of RP‐PVSK at q z = 0.75 Å −1 increases with the addition of PBMA and PPyMA polymers compared to PMMA, indicating a maintained ligand effect. [ 31,32 ] However, there is no apparent low‐n phase signal in bulk and DJ‐PVSK with PBMA and PPyMA. These results reflect that the mono‐amine ligand retains its interaction with perovskite in polymers comprising a benzene or pyrene functional group, which provides a suitable steric hindrance and π–π stacking.…”

Green synthesis of 3D cesium lead halide perovskite nanocrystals and 2D Ruddlesden–Popper nanoplatelets in menthol-based deep eutectic solvents

“…This lower angle diffraction is the characteristic signature of the regular stacking pattern in a RP NPL structure. [38][39][40][41] To have an idea about the distance of these stacked NPLs, small angle X-ray scattering (SAXS) has been performed (Fig. 5e) where the first diffraction peak is found to originate at 1.831.…”

Pressure-Induced Changes in the Phase Distribution and Carrier Dynamics of Quasi-Two-Dimensional Ruddlesden–Popper Perovskites

“…Hybrid organic–inorganic perovskites exhibit unique structural characteristics and excellent optical, electrical, and magnetic properties, integrating the benefits of both organic and inorganic components. − Therefore, they hold great promise for optoelectronic applications. − However, material stability and structural tunability remain significant challenges. The quasi-two-dimensional (quasi-2D) Ruddlesden–Popper (RP) hybrid metal halide perovskites feature a natural quantum well structure with layered octahedral inorganic quantum wells separated by organic chains.…”