Exciton Binding Energy Modulation in 2D Perovskites: A Phenomenological Keldysh Framework

Abstract

The alternating organic–inorganic layers of 2D perovskites induce quantum and dielectric confinement effects that strongly influence their electronic structure. To decouple the effects of screening environment from structural distortion, it systematically modifies the screening environment of 2D perovskites using a homologous series of organic spacers. This approach preserves the structure of the inorganic framework, enabling a clear investigation of the effect of the screening environment. The direct measurements reveal a notable divergence: while the exciton energy remains constant, the quasiparticle bandgap (Eg,qp) observed via photoelectron and inverse-photoelectron spectroscopies progressively increases with increasing spacer length. This trend leads to a significant increase in exciton binding energy (Eb), consistent with reports on layered perovskite systems. The structurally well-controlled approach experimentally validates that such variations originate from changes in the screening environment. To rationalize these observations, the Keldysh model is applied by introducing a phenomenological dielectric constant (ɛph), defined as a spatially averaged value. The results show that Eb exhibits a clear dependence on 1/ɛph, with fitted exponents closely compatible with the trend anticipated from the Keldysh model. Overall, this study provides an experimentally validated basis for predicting excitonic properties and engineering-oriented insights relevant to design in quasi-2D semiconductors.