Ligand-Size Related Dimensionality Control in Metal Halide Perovskites

Abstract

Low-dimensional organic–inorganic hybrid perovskites have triggered many fundamental research studies due to their intrinsic tunable photovoltaic properties, technologically relevant stability, and promising efficiency. However, there is limited information on how ligand size influences inherent structural and electronic properties of perovskites. To gain deeper understanding of ligand-size related structural and film properties, we fabricated a series of (L)2(MA) n‑1Pb n I3n+1 materials by introducing organic spacer ligands of n-CH3CH2NH3 (EA), n-CH3(CH2)2NH3 (PA), and n-CH3(CH2)3NH3 (BA) into the three-dimensional (3D) methylammonium (MA) lead iodide (MAPbI3) system with the same inorganic layer thickness (average ⟨n⟩ = 4). We demonstrate that the increased number of carbon atoms on ligands affects compatibility of ligands with the 3D [PbI6]4– framework, leading to different structural dimensionality and crystal orientation, largely explaining different electronic properties, crystal stability, and the consequent device performance of solar cells. This work provides key missing information on how ligand size influences structural dimensionality and desirable electronic properties for future stable and efficient solar cells.

Water‐Assisted Crystal Growth in Quasi‐2D Perovskites with Enhanced Charge Transport and Photovoltaic Performance

“…[ 4–7 ] The incorporation of hydrophobic bulky organic ligands can not only enhance the stability of perovskites with minimized permeation of water molecules but also increase the formation energy of perovskites to mitigate thermal degradation and ion migration. [ 8–10 ] These merits alongside the quantum confinement have rendered quasi‐2D perovskites great potentials for optoelectronic applications with a wide tunability on the bandgap or photophysical properties. [ 7 ] Unfavorably, quasi‐2D perovskites are generally associated with a large exciton binding energy (hundreds of meV) due to the insulating nature of bulky organic ligands and the specific layered arrangement.…”

Centimeter‐Sized Single Crystal of Two‐Dimensional Halide Perovskites Incorporating Straight‐Chain Symmetric Diammonium Ion for X‐Ray Detection

“…[11] Compared to 3D perovskite single crystals,2Danalogues have much higher structural stability,s uppressed ionic migration, stronger self-trapping,a nd anisotropic charge transport. [12][13][14][15][16] These benefits offer more tunability of the optoelectronic properties for larger degrees of freedom in chemistry and quantum mechanics.N owadays,R uddlesden-Popper (A) 2 A' nÀ1 M n Y 3n+1 ,where organic-inorganic layers are stacked by Va nD er Waals interaction between monoammonium spacers,are the most common 2D perovskite candidates for X-ray detection. Fore xample,X ua nd co-workers fabricated a10mmsized 2D double perovskite single crystal based on the organic cations of BA + (C 4 H 9 NH 3 + )a nd achieved as ensitivity of 4.2 mCGy air À1 cm À2 .…”

Cation Diffusion Guides Hybrid Halide Perovskite Crystallization during the Gel Stage

“…Recent reports also confirmed the bearing groups with the cation has profound influence on the phase distribution . In particular, the bulky alkyl group affects compatibility of cations to the inorganic [PbI 6 ] 4− framework leading to the preferential formation of small‐ n value species . It further suggests that tuning the composition of A site could systematically manipulate the phase segregation in the resultant film.…”