Determination of Dielectric Functions and Exciton Oscillator Strength of Two-Dimensional Hybrid Perovskites

Two-dimensional (2D) hybrid organic inorganic perovskite (HOIP) semiconductors have attracted widespread attention as a platform of next-generation optoelectronic devices benefiting from their naturally occurring and tunable multiple quantum-well-like (QW-like) structures, which enable a wide range of physical properties. Determining the intrinsic optical/electronic properties of 2D HOIPs is extremely important for further utility in photonic and optoelectronic devices. Here, we obtain the optical dielectric functions, complex refractive indices, and complex optical conductivities of both Ruddlesden–Popper (RP) and Dion–Jacobson (DJ) phases of 2D HOIPs, as a function of the perovskite QW thickness via spectroscopic ellipsometry over a broad energy range of 0.73–3.34 eV. We identify a series of feature peaks in the dielectric functions, and we explain the evolution of ground-state exciton peak with unit-cell thickness and changing excitonic confinement. We observe extraordinary values of optical extinction and electric loss tangents at the primary excitonic resonances and provide their detailed comparison with other known excitonic materials. Our study is expected to lay the foundation for understanding optical properties of pure-phase 2D HOIPs, which are critical and imperative for the accurate modelling of their photonic and optoelectronic devices.