Correlation of Dielectric Confinement and Excitonic Binding Energy in 2D Layered Hybrid Perovskites Using Temperature Dependent Photoluminescence

Abstract

In 2D layered hybrid perovskite like (PEA)2PbX4 (PEA = phenylethylammonium, X = Cl, Br, I), the high frequency dielectric constants for inorganic well layer (εw) and organic barrier (εb) are distinctly different. The dielectric contrast significantly influences their excitonic binding energy (Eex2D). Here we vary εw/εb by varying both the halide anion and the organic cation and then correlate the influence of the dielectric contrast on Eex2D. We estimate Eex2D by employing temperature (5.4–300 K) dependent photoluminescence (PL) and find that the change in Eex2D can be qualitatively monitored simply by measuring the PL lifetime at room temperature. Eex2D increases, and therefore, PL lifetime decreases by varying halide ions from Cl to Br to I for (PEA)2PbX4. Notably, this trend is opposite the case of 3D Pb-halide perovskites, where the excitonic binding energy decreases for X = Cl to Br to I. The opposite trend for 2D perovskites is explained by dielectric confinement, where we find Eex2D ∝ (εw/εb)m, with m as an unknown positive number and εw > εb. The dielectric confinement drastically diminishes with increasing εb. (EA)2PbI4 (EA = ethanolammonium) with εb = 37.7 shows Eex2D = 65 meV, as opposed to (PEA)2PbI4 with εb = 3.3 and Eex2D = 453 meV. This correlation of εw/εb with Eex2D is critical for optoelectronic applications of 2D layered perovskites.