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(2+n)](n−), that form in solutions of CH(3)NH(3)PbI(3) and PbI(2). The absorbance, photoluminescence (PL) and photoluminescence excitation (PLE) spectra of CH(3)NH(3)PbI(3) and PbI(2) solutions were measured in various solvents and a broad concentration range. Both CH(3)NH(3)PbI(3) and PbI(2) solutions exhibit absorption features attributed to [PbI(3)](1−) and [PbI(4)](2−) complexes. Therefore, we propose a new mechanism for the formation of polymeric polyiodide plumbates in solutions of pristine PbI(2). For the first time, we show that the [PbI(2+n)](n−) species in both solutions of CH(3)NH(3)PbI(3) and PbI(2) exhibit a photoluminescence peak at about 760 nm. Our findings prove that the spectroscopic properties of both CH(3)NH(3)PbI(3) and PbI(2) solutions are dominated by coordination complexes between Pb(2+) 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.