Elucidating the Structure and Photophysics of Layered Perovskites through Cation Fluorination

Optoelectronic devices based on layered perovskites containing fluorinated cations display a well-documented improved stability and enhanced performance over non-fluorinated cations. The effect of fluorination the crystal structure photophysics, however, has received limited attention up until now. Here, 3-fluorophenethylammonium lead iodide ((3-FPEA)2PbI4) single crystals are investigated their properties to ((PEA)2PbI4) variant compared. bulkier 3-FPEA cation increases distortion inorganic layers, resulting in blue-shifted absorbance photoluminescence. Temperature-dependent photoluminescence spectroscopy reveals an intricate exciton substructure both cases. shows hot-exciton resonances separated by 12 15 meV, values that much smaller than 40 46 meV found for (PEA)2PbI4. In addition, high-resolution spectra show emission at lower energies consists substructure, previously thought be line. With analysis resolved photoluminescence, vibronic progression is excluded as origin energies. Instead, part excitonic proposed originate from bound excitons. This work furthers understanding photophysics been heavily debated lately.