Origin of the Absorption Edge Fine Structure in Pb-Based Organic-Inorganic 1D Perovskites

Abstract

This current study, which utilized UV-vis variable temperature diffuse reflectance (DR) spectroscopy, has led to significant findings in the examination of the absorption spectra of three one dimensional (1D) perovskites: pyridinium lead bromide (PyPbBr3), piperidinium lead bromide (PipPbBr3), and piperidinium lead iodide (PipPbI3) in the temperature range of 100–300 K. The results, combined with our previously reported data on pyridinium lead iodide (PyPbI3), were analyzed. A distinct fine structure at the edge of the absorption/DR spectra was observed in all four compounds at cryogenic temperatures. The analysis of the temperature-stimulated evolution of the absorption edge fine structure allowed for the identification of the apparent fundamental transition in each spectrum, as well as two low-energy absorption bands shifted by 0.05–0.085 eV (ab1) and by 0.20–0.27 eV (ab2) at 100 K relative to the apparent bandgap. The absorption bands were found to be relatively narrow (fwhm ≤ 0.21 eV) and negligibly dependent on temperature, making them unobservable at ambient temperature due to the overlap with the red-shifted intrinsic absorption edge. The absorption bands showed similarities of the properties in all compounds and were tentatively assigned to electronic transitions within the Pb2+ ions in the [PbBr6] and [PbI6] units, given that Pb is the single common compositional element in the 1D perovskites investigated.