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, [PbI2+n ]n- , that form in solutions of CH3 NH3 PbI3 and PbI2 . The absorbance, photoluminescence (PL) and photoluminescence excitation (PLE) spectra of CH3 NH3 PbI3 and PbI2 solutions were measured in various solvents and a broad concentration range. Both CH3 NH3 PbI3 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 CH3 NH3 PbI3 and PbI2 exhibit a photoluminescence peak at about 760 nm. Our findings prove that the spectroscopic properties of both CH3 NH3 PbI3 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.

CsPb2 Br5 Single Crystals: Synthesis and Characterization.

CsPb2 Br5 is a ternary halogen-plumbate material with close characteristics to the well-reported halide perovskites. Owing to its unconventional two-dimensional structure, CsPb2 Br5 is being looked at broadly for potential applications in optoelectronics. CsPb2 Br5 investigations are currently limited to nanostructures and powder forms of the material, which present unclear and conflicting optical properties. In this study, we present the synthesis and characterization of CsPb2 Br5 bulk single crystals, which enabled us to finally clarify the material's optical features. Our CsPb2 Br5 crystal has a two-dimensional structure with Pb2 Br5- layers spaced by Cs+ cations, and exhibits approximately 3.1 eV indirect band gap with no emission in the visible spectrum.

K(4)[PbSe(4)]⋠en⋠NH(3) : a non-oxide, non-halide inorganic lead(IV) compound.

The first inorganic lead(IV) compound without oxygen, nitrogen or halogen ligands attached to the lead atom was obtained as the potassium salt of the tetraselenidoplumbate(IV) anion [Pb(IV) Se4 ](4-) . It is stable under inert conditions which may enable the transfer of the chemistry of chalcogenidogermanate(IV) or chalcogenidostannate(IV) materials, to the lead homologues.