Charge Transfer Boosting Moisture Resistance of Seminude Perovskite Nanocrystals via Hierarchical Alumina Modulation

Continuous-flow synthesis of CsPbI3/TiO2 nanocomposites with enhanced water and thermal stability

The inherent poor stability of CsPbI3 nanocrystals hinders the practical application of this material. Therefore, it is still a challenge to improve the stability of CsPbI3 nanocrystals and realize their large-scale continuous preparation. In this work, we report the preparation of CsPbI3/TiO2 nanocomposites with high stability by a microfluidic method. After the combination of CsPbI3 nanorods with TiO2, the PL intensity increased by 1.3 times under excitation at 577 nm due to the passivating effect of TiO2 on the surface of CsPbI3 nanorods and its carrier transport characteristics. Meanwhile, due to the coating of TiO2, the surface exposure area of CsPbI3 nanorods is reduced, which blocks external environmental effects to some extent and effectively improves the stability of CsPbI3 nanorods. Finally, an LED with a color gamut of 142% NTSC and a color temperature (CCT) of 3952 K was obtained by combining CsPbI1.5Br1.5/TiO2 and CsPbBr3/TiO2 nanocomposites with a blue light chip (455 nm). This study shows that the continuous and controllable synthesis of all inorganic halide perovskite nanocrystals by a microfluidic method is of great significance in the fabrication of high-performance optoelectronic materials and display devices.

Biocompatible Perovskite Nanocrystals with Enhanced Stability for White Light-Emitting Diodes

Recently emerged lead halide perovskite CsPbX3 (X = Cl, Br, and I) nanocrystals (PNCs) have attracted tremendous attention due to their excellent optical properties. However, the poor water stability, unsatisfactory luminescence efficiency, disappointing lead leakage, and toxicity have restricted their practical applications in photoelectronics and biomedical fields. Herein, a controllable encapsulated strategy is investigated to realize CsPbX3 PNCs/PVP @PMMA composites with superior luminescence properties and excellent biocompatibility. Additionally, the synthesized CsPbBr3 and CsPbBr0.6I2.4 PNCs/PVP@PMMA structures exhibit green and red emissions with a maximal photoluminescence quantum yield (PLQY) of about 70.24% and 98.26%, respectively. These CsPbX3 PNCs/PVP@PMMA structures show high emission efficiency, excellent stability after water storage for 18 months, and low cytotoxicity at the PNC concentration at 500 μg mL-1. Moreover, white light-emitting diode (WLED) devices based on mixtures of CsPbBr3 and CsPbBr0.6I2.4 PNCs/PVP@PMMA perovskite structures are investigated, which exhibit excellent warm-white light emissions at room temperature. A flexible manipulation method is used to fabricate the white light emitters based on these perovskite composites, providing a fantastic platform for fabricating solid-state white light sources and full-color displays.

Enhanced Photoelectric Properties of CsPbBr3 by SiO2 and TiO2 Bilayer Heterostructures

CsPbBr3/SiO2 heterostructures were synthesized by the hydrolysis reaction of a mixture of CsPbBr3 nanocrystals (NCs) and (3-aminopropyl)triethoxysilane (APTS) in air. Compared with CsPbBr3 NCs, the CsPbBr3/SiO2 heterostructures exhibit stronger photoluminescence (PL) intensity, longer lifetime of PL (∼40.5 ns), and higher PL-quantum yield (PLQY, ∼86%). The carrier dynamics of CsPbBr3/SiO2 was detected by the transient absorption (TA) spectrum. The experimental results show that SiO2 passivates the surface traps of CsPbBr3 NCs and enhances the PL intensity. However, photoelectrochemical impedance spectra (PEIS) demonstrate that the impedance of CsPbBr3/SiO2 is higher than that of CsPbBr3 NCs, which reduces carrier transport and extraction. Because the application of CsPbBr3/SiO2 in optoelectronics is limited, CsPbBr3/SiO2/TiO2 heterostructures were synthesized by the further reaction of tetrabutyl titanate (TBT). The TiO2 coating can reduce the impedance of the CsPbBr3/SiO2. Importantly, ∼68% of the PL intensity of CsPbBr3/SiO2 is retained. Compared with CsPbBr3/SiO2 and CsPbBr3 NCs, the CsPbBr3/SiO2/TiO2 demonstrates faster carrier transport (κct = 2.4 × 109 s-1) and higher photocurrent density (J = 76 nA cm-2). In addition, CsPbBr3/SiO2/TiO2 shows good stability under (ultraviolet) UV irradiation, along with water stability and thermal stability. Therefore, the double protection approach can enhance the stability of CsPbBr3 NCs and tune the optoelectronic properties of CsPbBr3 NCs.

In situ and General Multidentate Ligand Passivation Achieves Efficient and Ultra-Stable CsPbX3 Perovskite Quantum Dots for White Light-Emitting Diodes

Inorganic CsPbX3 perovskite quantum dots (PeQDs) show great potential in white light-emitting diodes (WLEDs) due to excellent optoelectronic properties, but their practical application is hampered by low photoluminescence quantum yield (PLQY) and especially poor stability. Herein,  we developed an in-situ and general multidentate ligand passivation strategy that allows for CsPbX3 PeQDs not only near-unit PLQY, but significantly improved stability against storage, heat, and polar solvent. The enhanced optical property arises from high effectiveness of the multidentate ligand, diethylenetriaminepentaacetic acid (DTPA) with five carboxyl groups, in passivating uncoordinated Pb2+ defects and suppressing nonradiative recombination. First-principles calculations reveal that the excellent stability is attributed to tridentate binding mode of DTPA that remarkably boosts the adsorption capacity to PeQD core. Finally, combining the green and red PeQDs with blue chip,  we demonstrated highly luminous WLEDs with distinctly enhanced operation stability, a wide color gamut of 121.3% of national television system committee, standard white light of (0.33,0.33) in CIE 1931, and tunable color temperatures from warm to cold white light readily by emitters' ratio. This study provides an operando yet general approach to achieve efficient and stable PeQDs for WLEDs and accelerates their progress to commercialization.

Lead immobilization for environmentally sustainable perovskite solar cells

Lead halide perovskites are promising semiconducting materials for solar energy harvesting. However, the presence of heavy-metal lead ions is problematic when considering potential harmful leakage into the environment from broken cells and also from a public acceptance point of view. Moreover, strict legislation on the use of lead around the world has driven innovation in the development of strategies for recycling end-of-life products by means of environmentally friendly and cost-effective routes. Lead immobilization is a strategy to transform water-soluble lead ions into insoluble, nonbioavailable and nontransportable forms over large pH and temperature ranges and to suppress lead leakage if the devices are damaged. An ideal methodology should ensure sufficient lead-chelating capability without substantially influencing the device performance, production cost and recycling. Here we analyse chemical approaches to immobilize Pb2+ from perovskite solar cells, such as grain isolation, lead complexation, structure integration and adsorption of leaked lead, based on their feasibility to suppress lead leakage to a minimal level. We highlight the need for a standard lead-leakage test and related mathematical model to be established for the reliable evaluation of the potential environmental risk of perovskite optoelectronics.

Suppression of Thermal Quenching for CsPbX3 (X = Cl, Br, and I) Quantum Dots via the Hollow Structure of SrTiO3 and Light-Emitting Diode Applications

All-inorganic perovskite quantum dots (PQDs, CsPbX₃, X = Cl, Br, and I) show outstanding application prospects in the field of photoelectric devices. In recent years, the development of PQDs has greatly improved their stability to water, oxygen, and light. However, thermal quenching of PQDs greatly limits their practical application. Herein, we embed PQDs into ATiO₃ (A = Ca, Ba, and Sr) of three different mesoporous spherical structures to explore the effect on thermal quenching of PQDs. Because of the unique mesoporous hollow microsphere structure and low thermal conductivity of SrTiO₃, it can effectively block the heat transfer and improve the thermal quenching of PQDs. The photoluminescence (PL) intensity of CsPbBr₃@SrTiO₃ composites is 72.6% of the initial intensity after heating to 120 °C. Moreover, the PL intensity of CsPbBr₃@SrTiO₃ composites remains about 80% of the initial value even when stored in air for 20 days or irradiated by 365 nm UV light for 48 h. A neutral white light-emitting diode is assembled by a blue chip, CsPbBr₃@SrTiO₃ composites, and red phosphor of K₂SiF₆:Mn⁴⁺, which has a color temperature of 5389 K and a color gamut covered 133% of National Television Standards Committee (NTSC).