Metal halide perovskites and perovskite-related materials have received tremendous research attention over the last decade for their remarkable optical and electronic properties with potential applications in various types of optoelectronics. Owing to the chemical stability and structural tunability, two-dimensional (2D) perovskites containing metal halide quantum wells sandwiched between organic spacers have shown great promise for many applications. While remarkable progress has been made in 2D perovskites from materials development to device integration, a fundamental understanding of the structure-property relationships of this class of materials has not been fully established yet. Here we report our investigation on the effects of organic spacers’ dipole moments on the photophysical properties of layered-2D perovskites in a model system containing phenethyl ammonium (PEA) based organic cations. Tuning the dipole moment of these organic spacers was achieved by adding electron-donating (methoxy phenethyl ammonium, MeOPEA) and electron-withdrawing (4-fluoro phenethyl ammonium, 4FPEA) substituents on the pristine PEA. With almost identical crystal structures, single crystals of layered-2D perovskites, (PEA)2PbBr4, (MeOPEA)2PbBr4, and (4FPEA)2PbBr4 are found to exhibit blue emissions peaked at 411, 414, and 417 nm, respectively. Interestingly, low-temperature photoluminescence measurements show the existence of self-trapped states in (MeOPEA)2PbBr4 with a broadband red emission peaked at 620 nm. The effects of the dipole moment on the electronic band structures of these materials have also been studied.

Effects of organic spacer’s dipole moment on the photophysical properties of layered-2D lead bromide perovskites

ACS Spring 2022

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