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

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 L2An-1MnX3n+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.