Abstract
Lead-free double perovskites are studied as an optional replacement to lead halide perovskites in optoelectronic applications. Recently, double-perovskite materials in which two divalent lead cations are replaced with an Ag+ and a trivalent cation have been demonstrated. The presence of a reactive silver cation and observations of metallic silver nanodecorations raised concerns regarding the stability and applicability of these materials. To better understand the nucleation and crystal growth of lead-free double perovskites, we explore the origin and role that metallic silver nanoparticles (NPs) play in the Ag-based Pb-free double-perovskite nanocrystal (NC) systems such as Cs2AgInCl6, Cs2AgSbCl6, Cs2AgBiCl6, and Cs2AgBiBr6. With major focus on Cs2AgInCl6 NCs, we show evidence supporting growth of the NCs through heterogeneous nucleation on preexisting metallic silver seeds. The silver seeds nucleate prior to injection of halide through reduction of the Ag+ ion by the aminic ligand. The presence of preexisting silver NPs is supported by a localized surface plasmon resonance (LSPR). The injection of halide precursor into the reaction mixture step initiates a fast nucleation and growth of the perovskite NC on the silver seed. The change in the dielectric medium at the interface of the silver NP results in a quantifiable red shift of the LSPR peak. In addition, we demonstrate charge transfer from the perovskite to the silver NP through photoinduced electrochemical Ostwald ripening of the silver NPs via UV irradiation. The ripened perovskite–metal hybrid nanocrystal exhibits modified optical properties in the form of quenched emission and enhanced plasmonic absorption. Future development of Ag-based double-perovskite NC applications depends on the ability to control Ag+ reduction at all synthetic stages. This understanding is critical for delivering stability and functionality for silver-based lead-free perovskite nanocrystals.
Highlights
The study of colloidal cesium lead halide perovskite (LHP)nanocrystals has grown rapidly in recent years due to their attractive optoelectronic properties
25 mg (0.125 mmol) of cesium acetate, 40 mg (0.25 mmol) of silver acetate, and 80 mg (0.25 mmol) of indium(III) acetate were placed into a 20 mL glass vial with a magnetic stirring bar. o-Xylene (5 mL), oleic acid (1.25 mL), and oleylamine (0.375 mL) were added, and the vial was heated to 100 °C for the desired amount of time
By the previously presented hypothesis, we find an explanation for the different populations of Ag NPs present in the end product of the reaction using classical nucleation theory (CNT)
Summary
The study of colloidal cesium lead halide perovskite (LHP). Nanocrystals has grown rapidly in recent years due to their attractive optoelectronic properties. LHP NCs have been employed in various applications, such as solar cells, lightemitting diodes, and photodetectors.[1,2] the use of lead remains a major setback due to its toxicity[3,4] and water solubility.[5] This has accelerated the study of alternative stable and environmentally sustainable metal halide perovskite NC systems. One optional replacement of lead is using a combination of a monovalent and a trivalent cations to form double perovskites (DP) with a stoichiometry of cAe2nMte+rMed+3Xon66−C9s(2AasgBseiBenr6,i1n0−F1i2guwrheic1hA)is. Research was an indirect band-gap semiconductor exhibiting long excited state lifetimes.[13]
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