Screening of the Electron-Hole Interaction in Two-Dimensional Perovskites

In hydrogen, the field between the electron-proton pair occurs across the vacuum. However, for an electron-hole pair within a semiconductor, the field occurs across a variety of neighboring particles such as valance electrons, phonons, and ions. A long-standing question has been, which of these neighboring particles contributes to the screening of the electron-hole interaction? Two-dimensional perovskites provide an ideal template to explore this question due to their large exciton binding energies (E_b) and highly frequency-dependent dielectric properties. Using density functional theory calculations, dielectric spectroscopy, and electroabsorption spectroscopy on over 30 distinct perovskite structures, we determine the frequency range of the dielectric spectrum that modulates E_b. Additionally, we answer several long-standing questions regarding dielectric and exciton properties in this important class of optoelectronic materials, namely, the dielectric values of the barrier and well layers, the value of E_b for the popular BA₂PbI₄ compound, the point where 2D MHPs transition from isolated quantum wells to superlattices, the correct model for describing exciton states in 2D MHPs, and the following effects on E_b: temperature, sample morphology, octahedral tilting, barrier polarizability, well polarizability, barrier length, and well length.