Two-Dimensional Halide Perovskites Incorporating Straight Chain Symmetric Diammonium Ions, (NH₃C_mH_2mNH₃)(CH₃NH₃)_n−1Pb_nI_3n+1 (m = 4–9; n = 1–4)

Abstract

Low-dimensional halide perovskites have recently attracted intense interest as alternatives to the three-dimensional (3D) perovskites because of their greater tunability and higher environmental stability. Herein, we present the new homologous 2D series (NHC HNH)(CHNH) PbI ( m = 4-9; n = 1-4), where m represents the carbon-chain number and n equals layer-thickness number. Multilayer ( n > 1) 2D perovskites incorporating diammonium cations were successfully synthesized by the solid-state grinding method for m = 4 and 6 and by the solution method for m = 7-9. Structural characterization by single-crystal X-ray diffraction for the m = 8 and m = 9 series ( n = 1-4) reveals that these compounds adopt the Cc space group for even n members and Pc for odd n members. The optical bandgaps are 2.15 eV for two-layer ( n = 2), 2.01 eV for three-layer ( n = 3), and 1.90 eV for four-layer ( n = 4). The materials exhibit excellent solution processability, and casting thin-films of the n = 3 members was successfully accomplished. The films show a clear tendency for the higher- m members to have preferred orientation on the glass substrate, with m = 8 exhibiting almost perfect vertical layer orientation and m = 9 displaying both vertical and parallel layer orientation, as confirmed by grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. The vertical layer orientation for the (NHCHNH)(CHNH)PbI member results in the best thermal, light, and air stability within this series, thus showing excellent potential for solar cell applications.

Compositional and Solvent Engineering in Dion–Jacobson 2D Perovskites Boosts Solar Cell Efficiency and Stability

“…First, we compared the stability of the 2D DJ (3AMP)(MA) 3 Pb 4 I 13 perovskite film with that of a representative 2D RP perovskite of (BA) 2 (MA) 3 Pb 4 I 13 . [54] We also found that FA cation in 3AMP-based 2D DJ perovskite improves not only the efficiency but also the stability. The insets in Figure 6a show that the films turned from black to yellow after the stability test.…”

Oriented and Uniform Distribution of Dion–Jacobson Phase Perovskites Controlled by Quantum Well Barrier Thickness

“…A possible reasonable explanation is that longer chain amines (PeDA and HDA) had lower solubility, allowing the first deposition of the lowest solubility n = 1 phase and hindering the formation of higher n phases. As the low n phase had lower lattice energy, it was the phase that was thermodynamically easier to form, so long chain amines exhibited more low n phases . Although the relative uniform phase could be obtained in PDA‐ and BDA‐ over PeDA‐ and HDA‐based DJ phase perovskite films, it should be noted that a small amount of low layer number perovskites (e.g., n = 2 or 3) were indeed present, as indicated by the presence of weak and multi‐Bragg spots or rings at 0 < q z < 1 and q xy = 0 in the PDA‐ and BDA‐based perovskite films (Figure f–i).…”

Reversible Thermochromism and Strong Ferromagnetism in Two‐Dimensional Hybrid Perovskites

“…Lowering the dimensionality to 2D with corner‐sharing octahedral layers and bulky organic cations separating perovskite layers gives rise to increased structural diversity and new functionalities . Besides, 2D hybrid perovskites have attracted much attention as alternative photovoltaic materials because of an improved stability arising from hydrophobic interactions, which block moisture diffusion in the material . In 2D perovskites, there is no Goldschmidt's tolerance factor restriction .…”