Disentangling the Luminescent Mechanism of Cs4PbBr6 Single Crystals from an Ultrafast Dynamics Perspective

The interface microenvironment mediates the emission of a semiconductor nanocluster via surface-dopant-involving direct charge transfer

The interface microenvironment of doped quantum dots (QDs) is crucial in optimizing the properties associated with the photogenerated excitons. However, the imprecision of QDs' surface structures and compositions impedes a thorough understanding of the modulation mechanism caused by the complex interface microenvironment, particularly distinguishing the contribution of surface dopants from inner ones. Herein, we investigated interface-mediated emission using a unique model of an atomically precise chalcogenide semiconductor nanocluster containing uniform near-surface Mn2+ dopants. Significantly, we discovered that Mn2+ ions can directly transfer charges with hydrogen-bonding-bound electron-rich alkylamines with matched molecular configurations and electronic structures at the interface. This work provides a new pathway, the use of atomically precise nanoclusters, for analyzing and enhancing the interface-dependent properties of various doped QDs, including chalcogenides and perovskites.

Efficient Exciton Dissociation through the Edge Interfacial State in Metal Halide Perovskite-Based Photocatalysts

Metal halide perovskites (MHPs) with superior optoelectronic properties have recently been actively pursued as catalysts in heterogeneous photocatalysis. Dissociating excitons into charge carriers holds the key to enhancing the photocatalytic performance of MHP-based photocatalysts, especially for those with strong quantum-confinement effects. However, attaining efficient exciton dissociation has been rather challenging. Herein, we propose a novel concept that the edge interfacial state can trigger anisotropic electron transfer to promote exciton dissociation. By taking Cs₄PbBr₆/TiO₂ mesocrystal heterojunction as a proof-of-concept, we demonstrate that the unique interfacial state at the edge of the system is generated by the defect-mediated chemical interaction and acts as a trap state, which brings on a directionally favored electron transfer from the center to edge regions, thereby significantly enhancing the desired exciton dissociation. Consequently, such a system achieves an excellent performance in photocatalytic CO₂ reduction. This paradigmatic work sheds light on the excitonic aspects for rational design of advanced photocatalysts toward high performance.

Phononic Fine-Tuning in a Prototype Two-Dimensional Hybrid Organic-Inorganic Perovskite System

The emerging two-dimensional (2D) lead-halide perovskite materials hold great promise for next-generation photovoltaic and optoelectronic applications, in which phonon engineering plays a crucial role. However, detailed mechanistic exploration related to phonon effects, especially from a dynamics perspective, remains rather limited. Herein, we present a systematic demonstration of phononic fine-tuning in a prototype 2D hybrid organic-inorganic perovskite (HOIP) system, i.e., phenethylammonium lead iodide [(PEA)₂PbI₄] with each hydrogen atom at positions 2 (ortho), 3 (meta), and 4 (para) on the PEA's phenyl group being replaced by a fluorine atom. Through a set of joint observations via ultrafast spectroscopy and temperature-dependent photoluminescence spectroscopy, we reveal that such a fluorination can subtly exert profound impacts on its structural distortion-induced phononic properties, including coherent phonon modes, phonon-phonon/electron-phonon interactions, and the hot-phonon bottleneck effect. This work highlights the significant importance of the atomic-level tailoring of organic cations in low-dimensional HOIP systems, which is usually ignored in conventional notion and practice.

Improvement in optical properties of Cs4PbBr6 nanocrystals using aprotic polar purification solvent

We demonstrate the influence mechanism on the optical property of Cs₄PbBr₆ during purification of solution with different protonated levels and polarities. During the purification process, organic groups originating from oleic acid (OA) and PbBr impurity on the surface of Cs₄PbBr₆ nanocrystals can be removed using high polarity aprotic and protonic solvents, and the number of Br vacancies (V_Br) can be reduced. The protonic polar solvent can not only etch the organic groups on the surface of nanocrystals, causing surface reconstruction and particle growth of nanocrystals, but also enter into the lattice of Cs₄PbBr₆ and react with the embedded CsPbBr₃. However, aprotic polar solvent decreases the particle size of Cs₄PbBr₆ nanocrystals with the increase in the solvent polarity. The optical properties of Cs₄PbBr₆ can be effectively improved using aprotic polar solvents as a purification solvent, which is very significant to improve the luminescence efficiency of perovskites.

We demonstrate the influence mechanism on the optical properties of Cs₄PbBr₆ during purification of solutions with different protonated levels and polarities.

Recent progress of zero-dimensional luminescent metal halides

This review provides in-depth insight into the structure–luminescence–application relationship of 0D all-inorganic/organic–inorganic hybrid metal halide luminescent materials.

In Situ Growth of 3D/2D (CsPbBr3/CsPb2Br5) Perovskite Heterojunctions toward Optoelectronic Devices

Two-dimensional (2D) CsPb₂Br₅ exhibits intriguing functions in enhancing the performance of optoelectronic devices in terms of environmental stability and luminescence properties when composited with other perovskites in different dimensionalities. We built a type I three-dimensional (3D) CsPbBr₃/2D CsPb₂Br₅ heterojunction through phase transition where CsPbBr₃ quantum dots in situ grew into 2D CsPb₂Br₅. A thorough growth mechanism study in combination with excited state dynamic investigations via femtosecond spectroscopy and first-principles calculations revealed that the type I hierarchy enhanced the stability of the heterojunction and spurred its luminous quantum yield by prolonging the lifetime of photogenerated carriers. Mixing the heterojunction with other phosphors yielded white-light-emitting diodes with a color rendering index of 94%. The work thus not only offered one new avenue for building heterojunctions by using the "soft crystal" nature of perovskites but also disentangled the enhanced luminescence mechanism of the heterojunction that can be harnessed for promising applications in the luminescence and display fields.

Negative photoconductivity in Cs4PbBr6 single crystal

Negative photoconductivity is firstly observed in large size Cs₄PbBr₆ single crystal that grown from Cs-rich solution. The Br vacancy and free excitons are responsible for this novel phenomena.

2D materials towards ultrafast photonic applications

Two-dimensional materials are now excelling in yet another arena of ultrafast photonics, including optical modulation through optical limiting/mode-locking, photodetectors, optical communications, integrated miniaturized all-optical devices, etc.