(Digital Presentation) Lead Halide Perovskite Quantum Dots for Mini-LEDs

Boosting carrier transport via functionalized short-chain conjugated ligands enables efficient green perovskite quantum dot light-emitting diodes

The past decade has witnessed the increasing interest in cesium lead halide perovskite quantum dots (PQDs) for their excellent optical properties with higher photoluminescence efficiency and tunable emission wavelengths widely applied in white LED, photovoltaic devices, etc. Here we report the preparation of CsPbBr3 PQDs by a facile anti-solvent method using conventional quaternary ammonium bromide (CTAB) as a double modifier-both proper alkyl group protection and bromine source donator. The as-formed PQDs are well-monodispersed cubes with a size of 10-15 nm and high photoluminescence quantum yield (PLQY) of up to 43 %. To enhance the stability of PQDs, CsPbBr3 @PS microspheres were formed by electrospraying process. The microspheres not only show excellent luminous properties, but exhibit much higher stability against air and UV light irradiation due to the super hydrophobic property of polystyrene.

Highly bright and ultra-stable cyan-emitting perovskite quantum dots encapsulated in zeolitic imidazolate framework-11 for advanced optoelectronic applications

Lead halide perovskite (CsPbX3, where X = Cl, Br, or I) quantum dots (QDs), with tunable optical and electronic properties, have attracted attention because of their promising applications in solar cells and next-generation optoelectronic devices. Hence, it is crucial to investigate in detail the fundamental size-dependent properties of these perovskite QDs to obtain high-quality nanocrystals for practical use. We propose a direct method for determining the concentration of solution-processed CsPbX3 QDs by means of spectrophotometry, in which the molar absorption coefficient (ε) is obtained using absorption and the Beer-Lambert law. By tuning the size of CsPbX3 QDs, we obtain their corresponding ε leading to a calibration curve for calculating the nanocrystal concentrations. The ε at the band edge for CsPbX3 (X = Cl, Br, or I) nanocrystals was found to be strongly dependent on the bandgap of the nanocrystals. We also obtained a reliable size dependence of the bandgap calibration curves to estimate the size of QDs from the absorption spectra.

Lead-halide perovskite quantum dots (PQDs) or more broadly, nanocrystals possess advantageous features for solution-processed photovoltaic devices. The nanocrystal surface ligands play a crucial role in the transport of photogenerated carriers and ultimately affect the overall performance of PQD solar cells. Significantly improved CsPbI3 PQD synthetic yield and solar-cell performance through surface ligand management are demonstrated. The treatment of a secondary amine, di-n-propylamine (DPA), provides a mild and efficient approach to control the surface ligand density of PQDs, which has an apparently different working mechanism compared to previously reported surface treatments. Using an optimal DPA concentration, the treatment can simultaneously remove both long-chain insulating surface ligands of oleic acid and oleylamine, even for unpurified PQDs with high ligand density. As a result, the electrical coupling between PQDs is enhanced, leading to improved charge transport, reduced carrier recombination, and a high power conversion efficiency approaching 15% for CsPbI3 -PQD-based solar cells. In addition, the production yield of CsPbI3 PQDs can be increased by a factor of 8. These results highlight the importance of developing new ligand-management strategies, specifically for emerging PQDs to achieve scalable and high-performance perovskite-based optoelectronic devices.

Lead halide perovskite quantum dots have drawn great attention in the wide-color gamut display area. However, their poor stability restricts their practical application as well as the leakage of a toxic lead element. In this study, an enclosed encapsulation strategy is adopted to form CsPbBr3 quantum dots embedded in the channels of molecular sieve SBA-15 with SiO2 outer layer as enclosing protection (denoted as CsPbBr3@SBA-15@SiO2), which is achieved through a facile solid-state sintering method with post-treatment. The stability of perovskite quantum dots is enhanced remarkably, of which the emission intently after immersion in water for two months can remain over 95% of the initial value. Efficient lead leakage is achieved simultaneously. The improvement mechanisms were elucidated via the micro- and spectral viewpoints. A wide color gamut of 114% NTSC is demonstrated based on the obtained green emitter. This study could provide new insights into designing stable and environmentally sustainable perovskite quantum dots and promote their applications.

Cesium lead halide perovskite quantum dots (QDs) have drawn extensive attention due to their excellent optical properties. However, their use is limited by poor stability. To enhance their stability, we electrospun perovskite-embedded fibers from composite CsPbX3 (X = Cl, Br, and I) perovskite QDs, blending with three polymers, poly(styrene-butadiene-styrene) (SBS), poly(methyl methacrylate) (PMMA), or polystyrene (PS), for the light-emitting diode (LED) applications. We found that the stretchable CsPbBr3@SBS fibers revealed the highest photoluminescence quantum yield, the CsPbBr3@PMMA fibers demonstrated a high thermal stability, and the CsPbBr3@PS fibers exhibited the best water-resistant stability. The photoluminescence intensity maintained 83% of its initial intensity for more than 3 months in water. Furthermore, the LED devices are manufactured from the blue chips and packaged with the core/shell red and green perovskite-based fibers by using biaxial electrospinning exhibited stable and highly efficient white luminescence. The luminance and efficiency are higher than 400% of the values of multilayered structures.

Surface defects and synthesis methods play important roles in the photoluminescence quantum yield (PLQY), stability, and the device performance of lead halide perovskite quantum dots (PQDs). In this study, we report a quadruple-ligand (tri-n-octylphosphine, didodecyldimethylammonium bromide, tetraoctylammonium bromide, and oleic acid) assisted room-temperature method for synthesizing CsPbBr3 QDs (RT-CsPbBr3) with an absolute PLQY of 83%. X-ray photoelectron spectroscopy confirms the high completeness of the Pb-Br octahedron through the absence of lead ions and presence of more bromide ions on the surface of RT-CsPbBr3 QDs. The exciton dynamics of RT-CsPbBr3 QDs is studied by using femtosecond transient absorption, time-resolved PL, and single-dot spectroscopy, which provide strong evidence of the suppression of trion formation compared with the hot injection-synthesized CsPbBr3 (HI-CsPbBr3) QDs. The white light-emitting diode (LED) fabricated with RT-CsPbBr3 PQDs and a K2SiF6:Mn4+ phosphor for backlight applications achieved a wide color gamut of 124% of the National Television System Committee (NTSC) standard.

Lead halide-based perovskite quantum dots (PQDs) have recently emerged as an important class of nanocrystal (NC) materials for optoelectronic and photoelectrochemical applications. Thanks to their intriguing features including tunable band gap, narrow emission, high charge carrier mobility, remarkable light-absorbing factors, and long charge diffusion length, there has been a surge in research on lead halide-based PQDs and their applications. In this review, we showcase the fundamentals of PQDs and two principal applications including PQD solar cells (PQDSCs) and photocatalytic conversion. First, a thorough discussion on PQDSCs, their structure, surface treatment, and interface engineering along with their recent progress are presented. It is highlighted that the improvement of the efficiency of PQDSCs from below 10% to beyond 16% in a matter of a few years has turned them into promising candidates for future SC applications. Subsequently, the application of PQDs in photocatalytic reactions such as hydrogen production, CO2 reduction, and organic compounds’ degradation is summarized. Not to mention that, despite the remarkable properties of PQDs in SCs and photocatalysis, the inferior stability of PV devices based thereon under operation as well as their poor tolerance under air, water, light, and heat impede their widespread application. For this, the practical efforts and possible solutions are extensively addressed. Finally, an outlook is provided, addressing further merits, and demerits of each application as well as prospective opportunities.

Owing to their large absorption cross-sections and high photoluminescence quantum yields, lead halide perovskite quantum dots (PQDs) are regarded as a promising candidate for various optoelectronics applications. However, easy degradation of PQDs in water and in a humid environment is a critical hindrance for applications. Here we develop a Pb-S bonding approach to synthesize water-resistant perovskite@silica nanodots keeping their emission in water for over six weeks. A two-photon whispering-gallery mode laser device made of these ultra-stable nanodots retain 80% of its initial emission quantum yield when immersed in water for 13 h, and a two-photon random laser based on the perovskite@silica nanodots powder could still operate after the nanodots were dispersed in water for up to 15 days. Our synthetic approach opens up an entirely new avenue for utilizing PQDs in aqueous environment, which will significantly broaden their applications not only in optoelectronics but also in bioimaging and biosensing.

All-inorganic lead halide perovskite quantum dots (CsPbBr3 QDs) are attracting significant research interests because of their highly efficient light-emitting performance combined with tunable emission wavelength facilely realized by ion exchange. However, blue emission from perovskite QDs with strong quantum confinement is rarely reported and suffers from lower luminescence efficiency. Here we report blue-emitting ultrasmall (∼3 nm) CsPbBr3 QDs with photoluminescence (PL) quantum yield as high as 68%. Using time-resolved and steady-state PL spectroscopy, we elucidate the mechanism of the highly efficient PL as recombination of excitons localized in radiative band tail states. Through analyzing the spectral-dependent PL lifetime and the PL line shape, we obtain a large band tail width of ∼80 meV and a high density of state of ∼1020 cm-3. The relaxation of photocarriers into the radiative tail states suppresses the capture by nonradiative centers. Our results provide solid evidence for the positive role of band tail states in the optical properties of lead halide perovskites, which can be further tailored for high-performance optoelectronic devices.

Ligand engineering of perovskite quantum dots for efficient and stable solar cells

All-inorganic lead halide perovskite quantum dots (PQDs) have attracted significant attention due to their exceptional optoelectronic properties and unique spin-related behaviors. This study investigates the interplay between hole spin coherence and photocharging processes in solution-processed CsPbCl3 PQDs by using time-resolved Faraday rotation spectroscopy. Our research reveals a room-temperature hole spin dephasing time of ∼60 ps and a hole g factor of ∼1.73. Photocharging dynamics are probed via a spin detection technique based on a prepump-pump-probe methodology, uncovering biphasic formation kinetics with time constants of 54 and 327 ps and three lifetimes of 62 μs, 335 μs, and >1 ms for the photocharged states. These multiscale dynamics are similarly observed in CsPbBr3 PQDs. This study provides a quantitative framework linking spin coherence to photocharging processes, deepening the understanding of spin-charge correlations in lead halide perovskites, and offering practical guidelines for optimizing quantum coherence in solution-processed nanomaterials.

Lead halide perovskite quantum dots (QDs) are controversial due to their high lead content. Tin, a low-toxic element with an outer electronic structure similar to that of Pb, becomes a strong candidate for preparing lead-free perovskite QDs. However, tin-based perovskite QDs, especially CsSnCl3 QDs, exhibit poor environmental stability. Herein, we proposed an strategy for highly stable CsSnCl3 QDs using an ionic liquid as a solvent and antioxidant and gelatin as a multidentate ligand and coating material through an in situ method ([AMIM]Cl/gelatin-QDs). The results showed that the abundant active groups of gelatin served as the nucleation growth center for QDs and further passivated QDs. At the same time, the long molecular chain of gelatin can coat the QDs to isolate the environment and fully protect QDs, and the size of QDs grown in gelatin was 5-10 nm. In addition, the oxidation resistance of ionic liquids and the halogen-rich environment formed also played an important role. Even if [AMIM]Cl/gelatin-QDs were treated with water and ultraviolet light simultaneously, its remaining fluorescence intensity was still above 60% within 72 h. Meaningfully, QDs endowed the composite system mildew resistance, which can resist the erosion of gelatin by molds, thereby realizing the system's long-term protection toward CsSnCl3 QDs.

Enhancing the stability of perovskite quantum dots CsPbX3 (X=Cl, Br, I) by encapsulation in porous Y2O3 nanoparticles for WLED applications