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

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