White-Light Emission and Structural Distortion in New Corrugated Two-Dimensional Lead Bromide Perovskites

Hybrid inorganic-organic perovskites are developing rapidly as high performance semiconductors. Recently, two-dimensional (2D) perovskites were found to have white-light, broadband emission in the visible range that was attributed mainly to the role of self-trapped excitons (STES). Here, we describe three new 2D lead bromide perovskites incorporating a series of bifunctional ammonium dications as templates which also emit white light: (1) alpha-(DMEN)PbBr4 (DMEN = 2-(dirnethylamino)ethylamine), which adopts a unique corrugated layered structure in space group Pbca with unit cell a = 18.901(4) angstrom, b = 11.782(2) angstrom, and c = 23.680(5) angstrom; (2) (DMAPA)PbBr4 (DMAPA = 3-(dimethylamino)-1-propylamine), which crystallizes in P21/c with a = 10.717(2) angstrom, b = 11.735(2) angstrom, c = 12.127(2) angstrom, and beta = 111.53(3)degrees; and (3) (DMABA)PbBr4 (DMABA = 4-dimethylaminobutylamine), which adopts Aba2 with a = 41.685(8) angstrom, beta = 23.962(5) angstrom, and c = 12.000(2) angstrom Photoluminescence (PL) studies show a correlation between the distortion of the PbBr6 octahedron in the 2D layer and the broadening of PL emission, with the most distorted structure having the broadest emission (183 nm full width at half-maximum) and longest lifetime (tau(avg) = 1.39 ns). The most distorted member alpha-(DMEN)PbBr4 exhibits white-light emission with a color rendering index (CRI) of 73 which is similar to a fluorescent light source and correlated color temperature (CCT) of 7863 K, producing cold white light.