Enhanced yield-mobility products in hybrid halide Ruddlesden–Popper compounds with aromatic ammonium spacers

Abstract

Hybrid halide Ruddlesden–Popper compounds are related to three-dimensional hybrid AMX₃ perovskites (e.g. where A is a monovalent cation, M is a divalent metal cation, and X is a halogen) with the general formula L₂A_n–1M_nX_3n+1 where L is a monovalent spacer cation. The crystal structure comprises perovskite-like layers separated by organic cation spacers. Here two Ruddlesden–Popper compounds with a conjugated cation, 2-(4-biphenyl)ethylammonium (BPEA) prepared by solvothermal and solvent evaporation techniques are reported. The structures of the two compounds: (BPEA)₂PbI₄ and (BPEA)₂(CH₃NH₃)Pb₂I₇, were solved by X-ray crystallography. The aromatic rings of the BPEA groups are well-separated in the organic layers leading to optical properties comparable to n = 1 and 2 hybrid halide Ruddlesden–Popper compounds with simpler alkyl ammonium cations. The ambient stability of both compounds over time was also confirmed by powder X-ray diffraction. Finally, the transient photoconductance, measured by time-resolved microwave conductivity, show that the compounds have maximum yield-mobility products respectively of 0.07 cm² V⁻¹ s⁻¹ and 1.11 cm² V⁻¹ s⁻¹ for (BPEA)₂PbI₄ and (BPEA)₂(CH₃NH₃)Pb₂I₇, both slightly enhanced over what has been measured for compounds with n-butylammonium spacer cations.