Indium Doping of Lead-Free Perovskite Cs2SnI6

Lead-rivet strategy of growing perovskite nanocrystals for excellent toxicity inhibition and spinning application

Lead halide perovskite has demonstrated remarkable potential in the wearable field due to its exceptional photoelectric conversion capability. However, its lead toxicity issue has consistently been subject to criticism, significantly impeding its practical application. To address this challenge, an innovative approach called lead-rivet was proposed for the in-situ growth of perovskite crystalline structures. Through the formation of S-Pb bonds, each Pb2+ ion was firmly immobilized on the surface of the silica matrix, enabling in situ growth of perovskite nanocrystals via ion coordination between Cs+ and halide species. The robust S-Pb bonding effectively restricted the mobility of lead ions and stabilized the perovskite structure without relying on surface ligands, thereby not only preventing toxicity leakage but also providing a favorable interface for depositing protective shells. The obtained perovskites exhibit intense and narrow-band fluorescence with full-width at half-maximum less than 23 nm and show excellent stability to high temperature (above 202 °C) and high humidity (water immersion over 27 days), thus making it possible to be used in varies textile technologies including melt spinning and wet spinning. The lead leakage rate of particles is only 4.15 % demonstrating excellent toxicity inhibition performance. The prepared fibers maintained good extensibility and flexibility which could be used for 3D-printing and textiles weaving. Most importantly, the detected Pb2+ leaching was negligible as low as to 0.732 ppb which meet the standard of World Health Organization (WHO) for drinking water (<10 ppb), and the cell survival rate remained 99.196 % for PLA fluorescent filament after 24 h cultivation which showing excellent safety to human body and environment. This study establishes a controllable and highly adaptable synthesis method, thereby providing a promising avenue for the safe utilization of perovskite materials.

In Search of a Double Perovskite in the Phase Triangle of Bromides CsBr-CuBr-InBr3

New bromide compounds A₂B^IB^IIIBr₆ with a double perovskite structure provide variety and flexibility of optoelectronic properties, and some of them are of poor toxicity in comparison with such popular lead halides. The promising compound with a double perovskite structure was proposed recently for the ternary system of CsBr-CuBr-InBr₃. Analysis of phase equilibria in the CsBr-CuBr-InBr₃ ternary system showed stability of the quasi-binary section of CsCu₂Br₃-Cs₃In₂Br₉. Formation of the estimated phase Cs₂CuInBr₆ by melt crystallization or solid-state sintering was not observed, most likely, as a result of higher thermodynamic stability of binary bromides CsCu₂Br₃ and Cs₃In₂Br₉. The existence of three quasi-binary sections was observed, while no ternary bromide compounds were found.

Controlled Reduction of Sn4+ in the Complex Iodide Cs2SnI6 with Metallic Gallium

Metal gallium as a low-melting solid was applied in a mixture with elemental iodine to substitute tin(IV) in a promising light-harvesting phase of Cs₂SnI₆ by a reactive sintering method. The reducing power of gallium was applied to influence the optoelectronic properties of the Cs₂SnI₆ phase via partial reduction of tin(IV) and, very likely, substitute partially Sn⁴⁺ by Ga³⁺. The reduction of Sn⁴⁺ to Sn²⁺ in the Cs₂SnI₆ phase contributes to the switching from p-type conductivity to n-type, thereby improving the total concentration and mobility of negative-charge carriers. The phase composition of the samples obtained was studied by X-ray diffraction (XRD) and ¹¹⁹Sn Mössbauer spectroscopy (MS). It is shown that the excess of metal gallium in a reaction melt leads to the two-phase product containing Cs₂SnI₆ with Sn⁴⁺ and β-CsSnI₃ with Sn²⁺. UV-visible absorption spectroscopy shows a high absorption coefficient of the composite material.

Phase Equilibria in Ternary System CsBr-AgBr-InBr3

The double perovskite halides A₂B^IB^IIIX₆ provide flexibility for various formulation adjustments and are of less toxicity in comparison with well-discussed complex lead halide derivatives. Such type of structure can be formed by replacing two Pb²⁺ ions in the cubic lattice with a pair of non-toxic heterovalent (monovalent and trivalent) metal cations, such as silver and indium. The aim of this work is to briefly characterize the phase equilibria in the ternary system CsBr-AgBr-InBr₃ and investigate the thermodynamic availability of synthesis of Cs₂AgInBr₆ double perovskite phase by solid-state sintering or melt crystallization. The results demonstrate the unfeasibility of the Cs₂AgInBr₆ phase but high stability of the corresponding binary bromides perspective for optoelectronics.