Tunable White-Light Emission in Single-Cation-Templated Three-Layered 2D Perovskites (CHCHNH)PbBrCl.

Two-dimensional (2D) hybrid halide perovskites come as a family (B)(A)PbX (B and A= cations; X= halide). These perovskites are promising semiconductors for solar cells and optoelectronic applications. Among the fascinating properties of these materials is white-light emission, which has been mostly observed in single-layered 2D lead bromide or chloride systems (n = 1), where the broad emission comes from the transient photoexcited states generated by self-trapped excitons (STEs) from structural distortion. Here we report a multilayered 2D perovskite (n = 3) exhibiting a tunable white-light emission. Ethylammonium (EA) can stabilize the 2D perovskite structure in EAPbBrCl (x = 0, 2, 4, 6, 8, 9.5, and 10) with EA being both the A and B cations in this system. Because of the larger size of EA, these materials show a high distortion level in their inorganic structures, with EAPbCl having a much larger distortion than that of EAPbBr, which results in broadband white-light emission of EAPbCl in contrast to narrow blue emission of EAPbBr. The average lifetime of the series decreases gradually from the Cl end to the Br end, indicating that the larger distortion also prolongs the lifetime (more STE states). The band gap of EAPbBrCl ranges from 3.45 eV (x = 10) to 2.75 eV (x = 0), following Vegard's law. First-principles density functional theory calculations (DFT) show that both EAPbCl and EAPbBr are direct band gap semiconductors. The color rendering index (CRI) of the series improves from 66 (EAPbCl) to 83 (EAPbBrCl), displaying high tunability and versatility of the title compounds.