Fig. 1: Cyclic organic cation-dependent STEs emission in 2D halide perovskites.

a Schematic of a representative C6 perovskite. The crystal structure includes one layer of inorganic octahedra sandwiched by a bilayer of cyclic organic cation. The grey, red, purple, and pink balls represent the Br, Pb, N and C atoms, respectively. b Schematic of amnio group penetration and the corresponding terminal (L₁) and bridging (L₂) connections. h is the amnio group penetration depth. The graded plane refers to the out-of-plane of the octahedral layer and \({D}_{{{\rm{tilt}}}}\) corresponds to the titling distortion. c Extracted Pb off-center displacement parameter and the out-of-plane octahedral tilting distortion as a function of amnio group penetration depth. d PL (colored scatters) and absorption (black dotted curves) spectra of 2D halide perovskites with different cyclic organic cations. The cyan and black shaded areas refer to the curve-fits for FE and STE emission, respectively. The red-dashed curve with arrow is the guide for the eye, indicating the shifting of the STEs emission’s center position. All the samples are excited with a CW laser at 360 nm. e The ratio of PLQY of STE emission to that of free exciton emission \({{{\rm{PLQY}}}}_{{{\rm{STE}}}}/{{{\rm{PLQY}}}}_{{{\rm{FE}}}}\) as a function of the ring size of cyclic cation. The error bar represents the standard deviation.