The Role Silver Nanoparticles Plays in Silver-Based Double-Perovskite Nanocrystals

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 Cs 2 AgInCl 6 , Cs 2 AgSbCl 6 , Cs 2 AgBiCl 6 , and Cs 2 AgBiBr 6 . With major focus on Cs 2 AgInCl 6 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.

Self‐Healing of Crystal Voids in Double Perovskite Nanocrystals Is Related to Surface Passivation

“…The HAADF‐STEM micrograph (Figure 1b) shows NCs decorated by bright contrast spherical silver nanoparticles discussed elsewhere. [ 41 ] The dark contrast rectangular feature is a void defect (marked with a red arrow) generated by the electron beam and framed by highly crystalline edges. Such crystallinity drew our attention, especially since facile crystal reconstruction to its original structure occurs when the void moves from the crystal edges toward its center (see Figure 1c–f).…”

Efficacy of Perovskite Photocatalysis: Challenges to Overcome

“…The exchange of Au­(III) ions from solution with Pb 2+ cations within the nanocrystal lattice creates a double halide perovskite structure, as Au­(I) and Au­(III) compensate charges for the exchanged Pb 2+ ions. Similarly, cation exchange or substitution with Ag + and Bi 3+ has resulted in the formation of double halide perovskites. − Photoirradiation of Cs 2 Au I Au II Br 6 NCs also leads to the ejection of gold from the nanocrystal lattice, re-forming CsPbBr 3 . Such an exchange with metal cations poses a challenge to the development of perovskite–metal heterostructures for photocatalysis.…”

Co-doping of tellurium with bismuth enhances stability and photoluminescence quantum yield of Cs2AgInCl6 double perovskite nanocrystals

“…† Notably, multiple dark spots belonging to metallic silver appeared on each Cs 2 AgInCl 6 :0% Te,1% Bi NC, demonstrating its limited structural stability under electron beam irradiation in TEM, although silver particles could form under certain synthesis as well. 17,39 In contrast, those spots tended to fade away with an increasing amount of tellurium precursors and were remarkably absent when the Te feeding ratio reached 8%, demonstrating the greatly improved lattice crystallinity and far better structural stability under an electron beam. The crystallinity of the perovskite NCs took a turn for the worse, however, on reaching an excessive Te feeding ratio of 12%, according to the reappearance of the dark spots in Fig.…”