Direct investigation of the reorientational dynamics of A-site cations in 2D organic-inorganic hybrid perovskite by solid-state NMR

Abstract

Limited methods are available for investigating the reorientational dynamics of A-site cations in two-dimensional organic–inorganic hybrid perovskites (2D OIHPs), which play a pivotal role in determining their physical properties. Here, we describe an approach to study the dynamics of A-site cations using solid-state NMR and stable isotope labelling. 2H NMR of 2D OIHPs incorporating methyl-d3-ammonium cations (d3-MA) reveals the existence of multiple modes of reorientational motions of MA. Rotational-echo double resonance (REDOR) NMR of 2D OIHPs incorporating 15N- and ¹³C-labeled methylammonium cations (13C,15N-MA) reflects the averaged dipolar coupling between the C and N nuclei undergoing different modes of motions. Our study reveals the interplay between the A-site cation dynamics and the structural rigidity of the organic spacers, so providing a molecular-level insight into the design of 2D OIHPs.

Crystal growth of two-dimensional organic–inorganic hybrid perovskites and their application in photovoltaics

“…Except for the pyrrole ring, the protonated nitrogen in amino amine or arylamine molecules has been used to count the charge of organic cations, which can be confirmed via the methods of infrared (IR) spectroscopy and nuclear magnetic resonance (NMR). 44 For organic cations, the primary ammonium cations with a long organic tail are the most suitable for 2D perovskites, which can ensure the efficient penetration to the site of [PbI 6 ] 4− and hydrogen bonding interaction between adjacent organic cations (van der Waals in R–P and D–J type organic molecules). 45 The organic tail part can be classified into linear, branched, and cyclic, which greatly influence the steric hindrance.…”

Molecular design for perovskite solar cells

“…For example, the existence of slight traces of guanidinium and ethyl ammonium in the A‐site Ruddlesden‐Popper perovskites leads to improved solar cell performance due to the smaller amount of charge carrier traps, 35 and mixing the spacing cations with the perovskite A cations helps fine tune the band gaps of the 2D Dion–Jacobson lead bromide‐based perovskite materials 36 . In addition, the reorientational dynamic in the A‐site cations of 2D halide perovskites is suggested to be crucial at the molecular level 37 . The A‐site radius dictates the halide perovskite structures 38,39 and fine tunes the band gaps of perovskites; however, it is difficult to define the most suitable ionic radius that optimizes the band gap toward the solar cell application because more factors such as the ionic radius of B and X site should be predefined to achieve more appropriate high‐level variables such as tolerance factors and octahedral factors.…”

Spin-Polarized Photocatalytic CO2 Reduction of Mn-Doped Perovskite Nanoplates

“…Artificial photosynthesis using solar-driven CO 2 reduction to value-added fuels and chemicals has attracted great attention recently because it provides a promising strategy for simultaneously tackling two important environmental issues of global warming and renewable energy. − However, because photocatalytic CO 2 reduction processes involve sluggish multielectron reaction kinetics, until now, the solar-driven CO 2 reduction conversion efficiency is still far from the satisfactory requirement for practical applications. , Typically, the conversion efficiency of photocatalytic CO 2 reduction is governed by several determining factors such as light-harvesting, CO 2 adsorption, charge separation and transport of photogenerated carriers, and redox reaction. , Extensive research has been devoted to pursuing efficient photocatalysts for CO 2 reduction by optimizing these key factors among materials. ,, Halide perovskite semiconductors are an emerging class of solution-processable optoelectronic materials for high-performance solar cells and also for light-emitting diodes (LEDs) because they exhibit superior physical properties such as high optical absorption coefficients, low-cost fabrications, tunable band gaps, long diffusion lengths, and long carrier lifetime. − Due to its excellent intrinsic optoelectronic properties, halide perovskites have also recently demonstrated their great potential in photocatalyst applications of solar-driven CO 2 reduction or hydrogen evolution. − Many efforts have been made to enhance the photocatalytic CO 2 reduction efficiencies and stabilities of halide perovskites. − For example, it has been known that an effective strategy to enhance the photocatalytic CO 2 reduction efficiency is to construct heterojunctions of halide perovskites with other nanoscale materials to promote charge separation and suppress charge recombination. ,,, The creation of built-in electric fields at heterojunctions may significantly enhance the photoinduced carrier separation efficiencies and their corresponding photocatalytic CO 2 reduction performance. ,, …”