Unraveling the Broadband Emission in Mixed Tin-Lead Layered Perovskites

摘要

Low-dimensional halide perovskites with broad emission are a hot topic fortheir promising application as white light sources. However, the physical originof this broadband emission in the sub-bandgap region is still controversial.This work investigates the broad Stokes-shifted emission bands in mixedlead-tin 2D perovskite films prepared by mixing precursor solutions of phenethylammoniumlead iodide (PEA_2PbI_4, PEA = phenethylammonium) and phenethylammoniumtin iodide (PEA_2SnI_4). The bandgap can be tuned by the lead-tinratio, whereas the photoluminescence is broad and significantly Stokes-shiftedand appears to be fairly insensitive to the relative amount of Pb and Sn. It isexperimentally observed that these low-dimensional systems show substantiallyless bandgap bowing than their 3D counterpart. Theoretically, this canbe attributed to the smaller spin–orbit coupling effect on the 2D perovskitescompared to that of 3D ones. The time-resolved photoluminescence shows anultrafast decay in the high-energy range of the spectra that coincides with theemission range of PEA_2SnI_4, while the broadband emission decay is slower,up to the microsecond range. Sub-gap photoexcitation experiments excludeexciton self-trapping as the origin of the broadband emission, pointing todefects as the origin of the broadband emission in 2D Sn/Pb perovskite alloys.