Metamorphoses of Cesium Lead Halide Nanocrystals

Abstract

Conspectus Following the impressive development of bulk lead-based perovskite photovoltaics, the “perovskite fever” did not spare nanochemistry. In just a few years, colloidal cesium lead halide perovskite nanocrystals have conquered researchers worldwide with their easy synthesis and color-pure photoluminescence. These nanomaterials promise cheap solution-processed lasers, scintillators, and light-emitting diodes of record brightness and efficiency. However, that promise is threatened by poor stability and unwanted reactivity issues, throwing down the gauntlet to chemists. More generally, Cs–Pb–X nanocrystals have opened an exciting chapter in the chemistry of colloidal nanocrystals, because their ionic nature and broad diversity have challenged many paradigms established by nanocrystals of long-studied metal chalcogenides, pnictides, and oxides. The chemistry of colloidal Cs–Pb–X nanocrystals is synonymous with change: these materials demonstrate an intricate pattern of shapes and compositions and readily transform under physical stimuli or the action of chemical agents. In this Account, we walk through four types of Cs–Pb–X nanocrystal metamorphoses: change of structure, color, shape, and surface. These transformations are often interconnected; for example, a change in shape may also entail a change of color. The ionic bonding, high anion mobility due to vacancies, and preservation of cationic substructure in the Cs–Pb–X compounds enable fast anion exchange reactions, allowing the precise control of the halide composition of nanocrystals of perovskites and related compounds (e.g., CsPbCl 3 ⇄ CsPbBr 3 ⇄ CsPbI 3 and Cs 4 PbCl 6 ⇄ Cs 4 PbBr 6 ⇄ Cs 4 PbI 6 ) and tuning of their absorption edge and bright photoluminescence across the visible spectrum. Ion exchanges, however, are just one aspect of a richer chemistry. Cs–Pb–X nanocrystals are able to capture or release (in short, trade) ions or even neutral species from or to the surrounding environment, causing major changes to their structure and properties. The trade of neutral PbX 2 units allows Cs–Pb–X nanocrystals to cross the boundaries among four different types of compounds: 4CsX + PbX 2 ⇄ Cs 4 PbBr 6 + 3PbX 2 ⇄ 4CsPbBr 3 + PbX 2 ⇄ 4CsPb 2 X 5 . These reactions do not occur at random, because the reactant and product nanocrystals are connected by the Cs + cation substructure preservation principle, stating that ion trade reactions can transform one compound into another by means of distorting, expanding, or contracting their shared Cs + cation substructu...

Switching on near-infrared light in lanthanide-doped CsPbCl3 perovskite nanocrystals

“…Cesium lead halide perovskite (LHP) CsPbX 3 (X = Cl, Br, I, or their mixture) nanocrystals (NCs) have attracted extensive interests due to their fascinating optical and electronic properties, which can find promising applications in photovoltaics and optoelectronics. [1][2][3][4][5][6][7][8] However, CsPbX 3 LHPs are direct bandgap semiconductors with bandgaps ranging between ∼3.1-1.7 eV (∼410-700 nm), [9][10][11][12][13] yielding photoluminescence (PL) properties limited to the visible spectral domain. It has been shown that introducing intermediate states in the mid bandgap of the host by metal ions doping, particularly for Yb 3+ with emission at ∼1.0 μm, is an effective strategy to tune the emission of LHP hosts to the near-infrared (NIR) region.…”

Phase Engineering of Cesium Manganese Bromides Nanocrystals with Color‐Tunable Emission

“…Furthermore, in a humid environment both 1D CsMnBr Cesium lead halide perovskite CsPbX 3 (X: Cl, Br, I) nanocrystals (NCs) with narrow photoluminescence (PL) emission band have been shown to be good emitters of red, green and blue light. [1][2][3][4][5][6][7][8][9][10][11] Major issues about these lead halide perovskites are their toxicity and poor stability. [12] This has triggered the development of lead-free metal halide perovskite NCs.…”

Halide Perovskites as Disposable Epitaxial Templates for the Phase-Selective Synthesis of Lead Sulfochloride Nanocrystals

“…One example is the field of colloidal semiconductors, where lead-based NCs are among the most explored compounds due to the appealing optoelectronic properties demonstrated by lead halide perovskites in the UV-VIS and by lead chalcogenides in the IR spectral ranges. 6,7,12,13,19 There, the combination of as little as four elements (Cs, Pb, X and E, where X = F, Cl, Br or I and E = S, Se or Te) can yield NCs of a variety of phases: the binaries CsX, PbX2 and PbE, 6,7,[20][21][22] the well-known cesium lead halides (Cs4PbX6, CsPbX3, and CsPb2X5), 12,19,23,24 and the still little explored lead chalcohalides (Pb4S3Br2 and Pb4S3I2). 25,26 All these compounds are often obtained under similar reaction conditions, and can therefore compete during the synthesis, requiring a careful tuning of the synthetic protocols to achieve the impurity-free synthesis of the desired product.…”