White-Light Emission from the Structural Distortion Induced by Control of Halide Composition of Two-Dimensional Perovskites ((C₆H₅CH₂NH₃)₂PbBr_4–<i>x</i>Cl_<i>x</i>)

Two-dimensional (2D) perovskites, which have a 2D orientation of the inorganic framework that determines largely the electronic characteristics and an organic cation in the interlayer that leads to a quantum well structure, have attracted a great deal of attention due to their superior stable optoelectronic properties. Especially, some of the greatest interest in 2D perovskites is their application in broad-band white-light emission for solid state lighting. We prepared (BZA)2PbBr4–xClx (BZA= benzylammonium and x = 0, 1.5, 2, 3, 3.5, 4) to tune the white-light emission. In the (BZA)2PbBr4 perovskite structure, the bond lengths of Pb–Br for PbBr62– exhibit the same lengths of 2.98 and 3.00 Å, respectively. However, in PbCl6 octahedra the bridging Pb–Cl distances were 2.83/2.88 Å and 2.85/2.88 Å, respectively. The 2D perovskite (BZA)2PbCl4 exhibits a turquoise light emission due to its highly distorted structure, whereas (BZA)2PbBr4 emits a narrow blue emission. We controlled the white emission by mixing the two compounds in proportion and changed the color from blue to white using the intermediate compound (BZA)2PbBr4–xClx (x = 1.5, 2, 3, 3.5). The intermediate compound (BZA)2PbBr4–xClx (x = 1.5, 2, 3, 3.5) shifted in the white space of Commission Internationale de l’Éclairage coordinates, which were (0.324, 0.383), (0.312. 0.369), (0.319, 0.374), and (0.338, 0.396), respectively. The correlated color temperature of all compounds was observed above 5000 K, which suggests that these perovskites could be utilized as “cold” white-light-emitting materials