Chemistry in the Molten State: Opportunities for Designing and Tuning the Emission Properties of Halide Perovskites

Starting from halide perovskites of (Cn)(2)PbX4 type (Cn =NH3 (+)(CH2)( n-1)COOH, n = 4, 5, 6; X = Br, Cl) exhibiting congruentmelting (at T (m) in the 130-200 & DEG;Crange), the solid solutions (Cn (1-x )Cn & PRIME; (x) )(2)PbBr4 and (Cn)(2)Pb(Br1-x Cl (x) )(4) havebeen prepared by a solvent-free process (synthesis in the molten state).The emission properties are slightly tuned in the case of mixed organiccation systems, whereas modifications are more dramatic in the caseof mixed halide systems, leading to emission properties through theentire visible region. A seriesof monolayered lead halide hybrid perovskites (HO2C(CH2)( n-1)NH3)(2)PbX4, named (Cn)(2)PbX4 (n = 4-6, X = Cl,Br), exhibiting a low congruent melting temperature (T (m)) (T (m) = 130 & DEG;C for (C4)(2)PbBr4), high stability in the molten state, andwhitish type emission, are reported. From the synthesis in the moltenstate, rare solid solutions of mixed organic cations (Cn (1-x )Cn & PRIME; (x) )(2)PbX4 (n, n & PRIME; = 4-6; X = Cl, Br; 0 & LE; x & LE;1) as well as solid solutions of mixed halides(Cn)(2)Pb(X1-y X & PRIME; (y) )(4) (n = 4-6; X, X & PRIME; = Cl, Br; 0 & LE; y & LE;1) have been prepared and characterized (thermalbehavior, powder X-ray diffraction (PXRD), photoluminescenceproperties). The impact of substitutions is significant on the thermalproperties, lowering the T (m) down to 100 & DEG;C for (C4)(2)Pb(Br0.25Cl0.75)(4). The emission properties are slightly tuned in the case ofmixed organic cation systems, whereas modifications are more dramaticin the case of mixed halide systems, leading to emission propertiesthrough the entire visible region. These results illustrate the greatopportunities offered by the congruent melting properties of halideperovskites allowing syntheses in the molten state.

Automated summary

Solid solutions of (Cn (1-x )Cn & PRIME; (x) )(2)PbX4 and (Cn)(2)Pb(Br1-x Cl (x) )(4) are prepared in the molten state, exhibiting tuned emission properties and modification of emission properties through the visible region.