Building Blocks of Hybrid Perovskites: A Photoluminescence Study of Lead-Iodide Solution Species

Abstract

In this work, we present a detailed investigation of the optical properties of hybrid perovskite building blocks, [PbI2+n]n−, that form in solutions of CH3NH3PbI3 and PbI2. The absorbance, photoluminescence (PL) and photoluminescence excitation (PLE) spectra of CH3NH3PbI3 and PbI2 solutions were measured in various solvents and a broad concentration range. Both CH3NH3PbI3 and PbI2 solutions exhibit absorption features attributed to [PbI3]1− and [PbI4]2− complexes. Therefore, we propose a new mechanism for the formation of polymeric polyiodide plumbates in solutions of pristine PbI2. For the first time, we show that the [PbI2+n]n− species in both solutions of CH3NH3PbI3 and PbI2 exhibit a photoluminescence peak at about 760 nm. Our findings prove that the spectroscopic properties of both CH3NH3PbI3 and PbI2 solutions are dominated by coordination complexes between Pb2+ and I−. Finally, the impact of these complexes on the properties of solid-state perovskite semiconductors is discussed in terms of defect formation and defect tolerance.