Hybrid Perovskite Solutions are Dominated by Mononuclear Pb Complexes

Hybrid organic-inorganic perovskites form the basis for the rapidly developing and best-performing modern photovoltaics. One of the main advantages of hybrid perovskites is simple film fabrication performed primarily by coating from highly coordinative aprotic solvents. Hybrid perovskite solutions are reported to have range of lead forms in solution from mono- and polyplumbate complexes to colloid particles of size in the range of 10 - 1000 nm and often coexisting. This creates uncertainties in interpretation of optical solution properties made without proper size characterization. Focusing on concentrated (C(PbI₂) = 0.7M) lead iodide solutions in dimethylformamide without colloid particles we demonstrate an absence of polyplumbate complexes by analyzing dependence of absorption and photoluminescence of lead iodide with change of iodide concentration. The reported results clarify uncertainties in composition and optical measurements of hybrid perovskite precursor solutions and establish a baseline for further characterization of polyplumbate complexes and colloid particles via optical methods.