Optical properties of PbI-based perovskite structures

Remarkable enhancement of the excitonic binding energy and oscillator strength is demonstrated in PbI-based layered perovskite compounds where quantum well layers of corner sharing PbI₆ octahedra are sandwiched by alkylammonium barrier layers with a much smaller dielectric constant. The enhancement is quantitatively explained by the image charge effect. By changing the dimensionality of PbI₆ networks, we observe a change in the exciton formation energy from 1.633 eV for three-dimensional networks to 342 eV for zero-dimensional isolated octahedra. This change is mainly ascribed to the quantum confinement effect.