The red light emission in 2D (C4SH3CH2NH3)2SnI4 and (C4OH7CH2NH3)2SnI4 perovskites

Abstract

Two-dimensional (2D) perovskites have a large exciton binding energy due to the structure of the quantum confinement, which produces a faster radiative recombination, and so are promising potential materials for light-emitting diodes. However, most of the highly efficient hybrid halide perovskites are based on the toxic Pb-based materials, so the replacement of Pb with less toxic and suitable substitute elements has been investigated for environmental efficient materials. Herein, we report the Sn-based 2D perovskites, which include (TPM)₂SnI₄ (TPM = C₄SH₃CH₂NH₃) and (TFF)₂SnI₄ (TFF = C₄OH₇CH₂NH₃), as red emission materials. Structural characterization by single crystal X-ray diffraction reveals that (TPM)₂SnI₄ undergoes a structural evolution from the orthorhombic space group Cmc2₁ (100 K) to Pbca (298 K), while the (TFF)₂SnI₄ perovskite exhibits the monoclinic space group P2₁/c at 100 K and 298 K. The inorganic framework of (TFF)₂SnI₄ was separated by the bilayer TFF chains with an empty space, which is an effective structure to increase the quantum confinement effect. The band gaps of the (TPM)₂SnI₄ (1.80 eV) and (TFF)₂SnI₄ (1.73 eV) compounds indicate the direct band gap semiconductor materials. From the time-resolved photoluminescence results, it can be seen that (TPM)₂SnI₄ produces uniform short emission (0.73 ns) throughout the entire powder crystals, whereas (TFF)₂SnI₄ has a uniform and long emission life time (47 ns). Temperature-dependent photoluminescence (PL) studies indicate that the (TPM)₂SnI₄ and (TFF)₂SnI₄ perovskites have a strong split red emission at low temperature due to the vibration of the inorganic framework. As the temperature increases, the PL spectra shift to the high energy region and the emission intensity decreases. The PL spectra of (TPM)₂SnI₄ and (TFF)₂SnI₄ perovskites have maximum peak wavelengths at 622 nm and 640 nm, and show the photoluminescence quantum yields of 0.30% and 1.71%, respectively.