Microwave-Enhanced Chemistry at Solid-Liquid Interfaces: Synthesis of All-Inorganic CsPbX3 Nanocrystals and Unveiling the Anion-Induced Evolution of Structural and Optical Properties

Doping Up the Light: A Review of A/B-Site Doping in Metal Halide Perovskite Nanocrystals for Next-Generation LEDs

All-inorganic metal halide perovskite nanocrystals (PeNCs) show great potential for the next generation of perovskite light-emitting diodes (PeLEDs). However, trap-assisted recombination negatively impacts the optoelectronic properties of PeNCs and prevents their widespread adoption for commercial exploitation. To mitigate trap-assisted recombination and further enhance the external quantum efficiency of PeLEDs, A/B-site doping has been widely investigated to tune the bandgap of PeNCs. The bandgap of PeNCs is adjustable within a small range (no more than 0.1 eV) by A-site cation doping, resulting in changes in the bond length of Pb-X and the angle of [PbX6]4. Nevertheless, B-site doping of PeNCs has a more significant impact on the bandgap level through modification of surface defect states. In this perspective, we delve into the synthesis of PeNCs with A/B-site doping and their impacts on the structural and optoelectronic properties, as well as their impacts on the performance of subsequent PeLEDs. Furthermore, we explore the A-site and B-site doping mechanisms and the impact of device architecture on doped PeNCs to maximize the performance and stability of PeLEDs. This work presents a comprehensive overview of the studies on A-site and B-site doping in PeNCs and approaches to unlock their full potential in the next generation of LEDs.

SERS-active plasmonic metal NP-CsPbX3 films for multiple veterinary drug residues detection

Sensitive and multiple veterinary drug residues detection is of important for food safety. Herein, uniform plasmonic Au nanobipyramids@Ag nanorods (Au NBP@Ag NR)-CsPbX₃ films with strong surface-enhanced Raman scattering (SERS) activity were constructed. The effects of different CsPbX₃ (X = Cl, Br, I, or mixed halogens) quantum dots (QDs) on the SERS performances of plasmonic metal NP films were investigated. CsPbI₃ QDs with large dielectric constant could be served as the dielectric media to retard the attenuation of electromagnetic evanescent wave, inducing strong electromagnetic strength for SERS enhancement. Plasmon-induced metal-to-perovskite interfacial charge transfer transition also contributed to SERS enhancement. SERS-active plasmonic Au NBP@Ag NR-CsPbI₃ films had excellent sensitivity and high reproducibility for quantitative, accurate and multiple detection of chloramphenicol, diazepam and malachite green in food matrix. This work deepened the understanding of the SERS enhancement mechanisms of plasmonic metal NP-perovskite hybrid heterostructures, showing potential prospects in food safety monitoring.

Revealing the effect of substitutional cation doping in the A-site of nanoscale APbI3 perovskite layers for enhanced retention and endurance in optoelectronic resistive switching for non-volatile bipolar memory devices

The effect of substitutional cation doping in the A-site of the nanoscale APbI₃ perovskite layer has been systematically investigated to achieve improvements in the charge-carrier dynamics and endurance of non-volatile bipolar (NVB) memory devices. We successfully adopted an energy-efficient, ultra-fast microwave-assisted solvothermal (MW-ST) synthesis route to prepare a sequence of APbI₃ (A = MA⁺, FA⁺, MAFA⁺, CsMA⁺ and CsMAFA⁺) perovskite powders with morphological transitions from cube-like polyhedrons to mixed polyhedrons and rods within 10 minutes at 120 °C without requiring any inert-gas atmosphere under high-humid ambient conditions. As-prepared APbI₃ powders were dissolved in DMSO:DMF, followed by the fabrication of a thin film via spin-coating. Upon annealing at 120 °C, the nanoscale self-assembled thin-film layer was formed. We observed that devices with the inorganic Cs⁺ cation with organic cations, (CsMAPI and CsMAFAPI) device showed improved endurance (3500 and 5000 cycles, respectively) and outstanding retention (60 000 s) owing to effective charge-carrier dynamics, compared to organic cation-based MAPI, FAPI and MAFAPI (1800, 1200 and 1300 cycles, respectively). Significantly, various cation-doped APbI₃-powders obtained via the MW-ST method remained to be stable for up to 5-months under high-humid conditions. Thus, enhanced optoelectronic-memory performance studies could provide an opportunity for next-generation nanoscale ORSNVB-memory devices for artificial intelligence (AI) and Internet of Things (IoT) applications.

Improved Performance of the Al2O3-Protected HfO2-TiO2 Base Layer with a Self-Assembled CH3NH3PbI3 Heterostructure for Extremely Low Operating Voltage and Stable Filament Formation in Nonvolatile Resistive Switching Memory

Herein, we report intriguing observations of an extremely stable nonvolatile bipolar resistive switching (NVBRS) memory device fabricated using HfO₂-TiO₂ topologically protected by Al₂O₃ as a stacked base layer for a CH₃NH₃PbI₃ (MAPI) electrolyte layer sandwiched between Ag and fluorine-doped tin oxide (FTO) electrodes. MAPI has been successfully synthesized by a rapid microwave-solvothermal (MW-ST) method within 10 min at 120 °C without requiring any inert gas atmosphere using low-cost precursors and solvents. Subsequently, MAPI powders are dissolved in aprotic solvents (DMF/DMSO = 8:2), and a spin-coated thin film is allowed to recrystallize upon annealing at 120 °C via a solution-based nanoscale self-assembly process. The fabricated memory device with the Ag/MAPI/Al₂O₃/TiO₂-HfO₂/FTO configuration shows an enhanced resistance ratio of 10⁵ for >10⁴ s at an extremely lower operating voltage (SET +0.2 V, RESET -0.2 V) when compared to that of the pristine MAPI device (±1 V, 10², 10⁴ s). We show that the memory device also exhibits a remarkable endurance of ≥3500 cycles due to the Al₂O₃ robust coating on the HfO₂-TiO₂ layer, facilitating prompt heterojunction formation. Thus, the adopted innovative strategies to prepare structurally and optically stable (∼1.5 years) MAPI under high-humid conditions could offer enhanced performance of NVBRS memory devices for medical, security, internet of things (IoT), and artificial intelligence (AI) applications.

Ligand-flexible synthesis of strongly confined perovskite nanocrystals: a microwave synthetic approach

Perovskite nanocrystals (PNCs) and their strongly confined versions have traditionally been synthesized via hot injection methods. However, there is a pressing need for a new synthesis method that offers more flexible surface chemistry, improved optical properties, and greater sample stability. Here we explore and exploit the recently introduced microwave (MW) synthesis method, focusing on temperature and coating ligands, including a polymer ligand for which the hot injection method is unsuitable. The optimized microwave synthetic protocols produce PNCs with better exciton definition, lower polydispersity, and stronger ligand attachment than their hot injection counterparts. A variety of characterization techniques were employed to compare the properties of PNCs produced by the hot injection versus microwave methods. Insight into the molecular basis for the improved PNC properties was provided by FTIR and several NMR experiments that revealed the nature of the attachment of different ligands and their interactions with the PNCs. The overall results demonstrate that MW synthesis is a promising alternative to the HI method, particularly if smaller PNCs with strong quantum confinement are desired.