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

In this work, we present a detailed investigation of the optical properties of hybrid perovskite building blocks, [PbI ] , that form in solutions of CH NH PbI and PbI . The absorbance, photoluminescence (PL) and photoluminescence excitation (PLE) spectra of CH NH PbI and PbI solutions were measured in various solvents and a broad concentration range. Both CH NH PbI and PbI solutions exhibit absorption features attributed to [PbI ] and [PbI ] complexes. Therefore, we propose a new mechanism for the formation of polymeric polyiodide plumbates in solutions of pristine PbI . For the first time, we show that the [PbI ] species in both solutions of CH NH PbI and PbI exhibit a photoluminescence peak at about 760 nm. Our findings prove that the spectroscopic properties of both CH NH PbI and PbI solutions are dominated by coordination complexes between Pb 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.