Surface Ligands for Perovskite Quantum Dots.

The combination of the quantum confinement effect of quantum dots (QDs) and unique photoelectric properties of perovskite semiconductors make perovskite quantum dots (PQDs) a promising candidate for photoelectric devices. To truly unlock their potential, a deep understanding of structure-property relationship is paramount. Among the various factors influencing this relationship, the role of surface ligands cannot be overstated. The polarity, conductivity, stability, and interaction effects of these ligands with QD surfaces create complicated ligand-QDs relationships, which greatly influences the successful synthesis of QDs. In essence, the surface chemistry of ligands serves as a critical determinant in shaping the properties of both the resulting QDs and QD-based devices. To address this, our paper introduces an innovative approach to studying ligands, utilizing their inherent functional groups as a classification criterion. It is begun by discussing the types of surface defects of PQDs and the functional groups used for passivation, emphasizing the importance of analyzing ligands based on their functional groups. Then the passivation mechanisms of ligands with various functional groups and their impact on enhancing QD performance are delved into. Ultimately, this paper summarizes and offers several design principles and rules for PQDs surface ligands that can be applied in most scenarios.

Flexible Soft X-Ray Image Sensors based on Metal Halide Perovskites With High Quantum Efficiency.

Soft X-ray imaging is a powerful tool to explore the structure of cells, probe material with nanometer resolution, and investigate the energetic phenomena in the universe. Conventional soft X-ray image sensors are by and large Si-based charge coupled devices that suffer from low frame rates, complex fabrication processes, mechanical inflexibility, and required cooling below -60 °C. Here, a soft X-ray photodiode is reported based on low-cost metal halide perovskite with comparable performance to commercial Si-based device. Nanothrough network electrode minimized the optical loss due to the shadowing of insensitive layers, while a multidimensional perovskite heterojunction is generated to reduce the photo-generated carrier loss. This strategy promoted a record quantum efficiency of 8 × 103% without cooling, several orders of magnitude greater than the previously achieved. Flexible and curved soft X-ray imaging arrays are fabricated based on this high-performance device structure, demonstrating stable soft X-ray response and sharp imaging capabilities. This work highlights the low-cost and efficient perovskite photodiode as a strong candidate for the next-generation soft X-ray image sensors.

The Deepest Blue: Major Advances and Challenges in Deep Blue Emitting Quasi-2D and Nanocrystalline Perovskite LEDs.

In this review, the recent development of blue perovskite light-emitting diodes (PeLED) are summarized. On deep-blue (≤465 nm) perovskite nanomaterials of different structural forms are mainly focused, including nanocrystals (NCs), quantum dots (QDs), nanoplatelets (NPLs), quasi-2D thin film, 3D bulk thin film, as well as lead-free perovskite nanomaterials. The current challenges are also examined in producing efficient deep-blue PeLED, such as material and spectral instability, imbalance charge transport, Joule heat impact, and poor optoelectronic performance. Several strategies are further discussed to overcome these challenges and achieve efficient deep-blue PeLED for next-generation display technology.

Halide Perovskite Induces Halogen/Hydrogen Atom Transfer (XAT/HAT) for Allylic C-H Amination.

Allylic C-H amination has emerged as a powerful tool to construct allylamines, common motifs in molecular therapeutics. Such reaction implies an oxidative path for C-H activation but furnishes reductive amines, inferring mild oxidants' inactivity for C-H oxidation but strong oxidants' detriment to products. Herein we report a heterogeneous catalytic approach that manipulates halogen-vacancies of perovskite photocatalyst and exploits halogenated-solvents (i.e. CH2Cl2, CH2Br2) as mild oxidants for selective C-H allyl amination with 19,376 turnover. CsPbBr3 nanocrystals induce cooperative hydrogen-atom-transfer (HAT, C-H oxidation, and halogen-vacancy CsPbBr3-x formation) and halogen-atom-transfer (XAT, CsPbBr3-x-induced solvent reduction) under a radical chain mechanism. Terminal/internal olefins are amenable to forge aromatic/aliphatic, cyclic/acyclic, secondary/tertiary allylamines (70 examples), including drugs or their derivatives.

Bright Structural-Phase-Pure CsPbI3 Core-PbSO4 Shell Nanoplatelets With Ultra-Narrow Emission Bandwidth of 77 meV at 630 nm.

Achieving a narrow emission bandwidth is long pursued for display applications. Among all primary colors, obtaining pure red emission with high visual perception is the most challenging. In this work, CsPbI3 halide perovskite nanoplatelets (NPLs) with rigorously controlled 2D  [PbI6]4- octahedron layer number (n) are demonstrated. A perovskite core-PbSO4 shell structure is designed to prevent aggregation and fusion between NPLs, enabling consistent thickness and quantum confinement strength for each NPL. Consequently, exact n = 4 CsPbI3 NPLs are demonstrated, exhibiting emission peaks around 630 nm, with very narrow spectral bandwidths of <24 nm and high absolute photoluminescence quantum yields up to 85%. The emission of n = 4 NPLs falls exactly within the pure-red region, closely aligning with the International Telecommunication Union Recommendation BT.2020  standard. Measurements suggest predominant stability and color homogeneity compared to traditional red-emitting CsPbIxBr3- x nanocrystals. Finally, proof-of-concept pure-red emissive light-emitting diodes (LEDs) are demonstrated by integrating n = 4 CsPbI3 NPLs films with a blue LED chip, showing an excellent external quantum efficiency of 18.3% and high brightness exceeding 3 × 106 nits. Stringent requirements for future display technologies, are satisfied based on the high color purity, stability, and brightness of CsPbI3 NPLs.

Recent Advances in Perovskite-Based Flexible Electroluminescent Devices.

Perovskite-based flexible electroluminescent (EL) devices are emerging as promising candidates in the display field due to their exceptional optoelectronic properties and potential for cost-effective production. However, simultaneously achieving high EL performance, excellent flexibility and stretchability, robust mechanical strength, and diverse applications remains a significant challenge. In this review, we provide a comprehensive overview of the latest developments in perovskite-based flexible EL devices, covering both direct-current (DC) and alternating-current (AC) electroluminescent formats. Our discussion encompasses the materials, working principles, device architectures, failure mechanisms, optimization strategies, and practical applications. Through this review, we aim to deepen our understanding of the current challenges and future directions of perovskite-based flexible light-emitting technologies, hoping to facilitate their potential commercial applications.

Electronic States of Single Perovskite Quantum Dots in Weak and Strong Interaction Regimes: Implications in Electrically Pumped Quantum Emitters.

We investigate the effect of Coulomb interactions on the electronic states of a single perovskite quantum dot (PQD), CsPbBr3, through scanning tunneling microscopy/spectroscopy (STM/S). Under a weak interaction regime, where the time-averaged occupation of electrons in a PQD remains zero, the peaks observed in the differential tunneling conductance (dI/dV) spectrum correspond to the single-particle density of states (DOS) without any electron-electron correlation. However, with a shorter tunnel distance between the STM tip and PQD, additional electrons are trapped in the QD, leading to a strong interaction regime with well-defined electronic fine structures due to the lifting of spin degeneracy in the conduction bands. Interestingly, we observe that the strong Coulomb interaction can modify the spin-orbit coupling (SOC) strength in the PQDs. We have concluded that the energy levels under a strong electron-electron interaction regime are of utmost importance since they will be applicable to electrically pumped PQD-based single photon quantum emitters.

Enhancing Perovskite Solar Cell Performance through Propylamine Hydroiodide Passivation.

In recent years, the power conversion efficiency of perovskite solar cells has increased rapidly. Perovskites can be prepared using simple and cost-effective solution methods. However, the perovskite films obtained are usually polycrystalline and contain numerous defects. Passivation of these defects is crucial for enhancing the performance of solar cells. Here, we report the use of propylamine hydroiodide (PAI) for defect passivation. We found that PAI can result in higher-efficiency cells by reducing the defects and suppressing non-radiative recombination. Consequently, n-i-p perovskite solar cells with a certificated efficiency of 21% were obtained. In addition, PAI exhibited excellent performance in p-i-n devices by serving as a buried interface layer, leading to an improved efficiency of 23%.

Self-Assembled Hybrid Halide Perovskite Quantum Wire Bundle/Dot for Multiband Applications.

In this study, self-assembled halide perovskite quantum wire bundles (QWBs)/quantum dots (QDs) are fabricated using a room temperature-based formation method. The one-dimensional (1D) perovskite-based QWB structures incorporate zero-dimensional QDs within a composite quantum structure. Transmission electron microscopy reveals that quantum wires with diameters ranging from tens of nanometers to approximately 200 nm maintain a single-crystal atomic arrangement in a bundle form. Conversely, QDs are uniformly distributed within the single-phase wire and appear as black dots < 10 nm. Photoluminescence analysis identifies the multiband characteristics of the emissions. The 420-440 nm band is attributed to 1D QWB, whereas the peak appearing in the 530-550 nm range corresponds to lead halide PbBr2 QDs. Thus, the proposed self-assembled 1D QWB/QD composite structure exhibits novel multiband physical properties in the 420-440 and 530-550 nm bands; it offers new opportunities for designing materials with potential applications in optoelectronic devices.

Constructing S-scheme heterojunction Cs3Bi2Br9/BiOBr via in-situ partial conversion to boost photocatalytic N2 fixation.

The judicious construction of interfaces with swift charge communication to enhance the utilization efficiency of photogenerated carriers is a viable strategy for boosting the photocatalytic performance of heterojunctions. Herein, an in-situ partial conversion strategy is reported for decorating lead-free halide perovskite Cs3Bi2Br9 nanocrystals onto BiOBr hollow nanotube, resulting in the formation of an S-scheme heterojunction Cs3Bi2Br9/BiOBr. This unique in-situ growth approach imparts a closely contacted interface to the Cs3Bi2Br9/BiOBr heterojunction, facilitating interfacial electron transfer and spatial charge separation compared to a counterpart (Cs3Bi2Br9:BiOBr) fabricated via traditional electrostatic self-assembly. Additionally, the establishment of an S-scheme charge transfer pathway preserves the robust redox capability of photogenerated carriers. Furthermore, the free electron transfer from Cs3Bi2Br9 to BiOBr promotes the activation of the NN bond and diminishes the energy barrier associated with the rate-determining step in the N2 reduction process. Consequently, the Cs3Bi2Br9/BiOBr heterojunction exhibits highly selective photocatalytic N2 reduction to NH3 (nearly 100 %) at a rate of 130 µmol g-1 h-1 under simulated sunlight (100 mW cm-2), surpassing BiOBr, Cs3Bi2Br9, and Cs3Bi2Br9:BiOBr by factors of 6, 4, and 2, respectively.