Optical Characterizations for Broadening Emissions from Doping of the Two-Dimensional Tin–Lead Perovskite Films

In this work, we present the optical properties of two-dimensional (2D) perovskite films of BA2SnxPb(1–x)I4 with x = 0–1. The excitonic absorption peaks of the fabricated perovskite samples were shown to shift to lower energies with increase of the Sn proportions in the films, whereas their emission spectra were shown to display dramatic Stokes shifts and spectral broadening from 600 to 1100 nm when compared with their pristine analogues. Power-dependent PL studies indicate that the emissions in the fabricated 2D perovskite samples arise from the self-trapping of excitons, while the spectral broadening originates from the production of multiple defect states upon doping of small amounts of Sn in the Pb-rich samples. The bandwidths of the emission spectra of the Pb–Sn mixed 2D perovskite samples were larger when the Pb proportion was higher than the Sn proportion, a key indicator for increasing the bandwidth of the white-light emission. TA spectral studies reveal that the nature of trap states plays a prominent role in the spectral broadening of the emission of the Pb-rich perovskite samples.