Recently, the pursuit of high photoluminescence quantum yields (PLQYs) for blue emission in perovskite nanocrystals (NCs) has attracted increased attention because the QY of blue NCs lags behind those of green and red ones severely, which is fatal for three-primary-color displays. Here, we propose an in situ PbBr 6 4− octahedra passivation strategy to achieve a 96% absolute QY for the ultrapure (line width = 12 nm) blue emission from CsPbBr 3 nanoplatelets (NPLs), and both values rank first among perovskite NCs with blue emission. From the aspect of constructing intact PbBr 6 4− octahedra, additional Br − was introduced to drive the ionic equilibrium to form intact Pb−Br octahedra. The reduced Br vacancy and inhibited nonradiative recombination processes are well proved by reduced Urbach energy, increased Pb−Br bonds, and slower transient absorption delay. Blue light-emitting diodes (LEDs) using NPLs were fabricated, and a high external quantum efficiency (EQE) of 0.124% with an emission line width of ∼12 nm was realized. This work will provide good references to break the "blue-wall" in perovskite NCs.

bonds. [18,19] The formation of hydrogen bonds reduces the coulombic interactions between lead and bromide ions, and then ammonium ligands will fall off from the QD surface along with bromide ions (Scheme 1a left). [20] On the other hand, the deprotonated ammonium ligands cannot interact with the CsPbBr 3 QDs.Therefore, the use of a single ligand without amine groups and reversible processes could overcome the purification stability problem, as shown recently by Yassitepe et al, who developed an aminefree method using only oleic acid (OA) as ligands. [21] The resulting CsPbBr 3 QDs could be washed several times without size increase or emission shift (Scheme 1a middle); however, the QY of these QDs was relatively low and the long-term stability was poor. The low QY results from the presence of enormous surface bromide vacancies (V Br ), since V Br exhibited obvious negative exciton trapping effect (Scheme 1b middle). [22] The groups of both Xia and Alivisatos recently confirmed the effect of V Br in their very recent works and near 100% QY can be achieved swimmingly by compensating Br ions with any bromides during or after synthesis (Scheme 1b left). [23,24] Hence, it seems contradictory that considering the QY, surface V Br should be avoided, while on account of good stability, ammonium which interacts with Br atoms should be excluded. To reduce the V Br density and reversible protonation, Kovalenko et al. introduced several kinds of zwitterionic ligands. [15,25] CsPbBr 3 QDs maintained high QY values of ≈80% and exhibited good purification stability. However, the preparation procedures were complicated, and even required precursor synthesis. Tan et al. reported the preparation of highly luminescent and stable CsPbBr 3 QDs prepared with addition of octylphosphonic acid (OPA). [26] However, in addition to OPA, the preparation also required the introduction of OA and trioctylphosphine oxide (TOPO), complicating the mechanism because TOPO and OA can also passivate and efficiently stabilize the CsPbBr 3 surface. [27,28] Additionally, OPA is insoluble in octadecene and is unable to dissolve PbBr 2 without TOPO. [29] In this work, we propose a concept of equivalent ligand, hypothesizing that if a ligand can play a role similar to Br ions to a certain extent and form strong interaction with lead ions (surfactant), then the problems of V Br and weak interaction can be solved simultaneously. The simplest source of Br ions is HBr, andThe stability and optoelectronic device performance of perovskite quantum dots (Pe-QDs) are severely limited by present ligand strategies since these ligands exhibit a highly dynamic binding state, resulting in serious complications in QD purification and storage. Here, a "Br-equivalent" ligand strategy is developed in which the proposed strong ionic sulfonate heads, for example, benzenesulfonic acid, can firmly bind to the exposed Pb ions to form a steady binding state, and can also effectively eliminate the exciton trapping probability due to bromide vacancies. From these two aspects, the s...

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All inorganic halide perovskite (IHP) nanocrystals (NCs) have emerged as a new class of optoelectronic materials for various applications. Surface ligands as surface passivators are essential components of nucleation and growth processes, photoluminescence quantum yields (PL QY), stability, and photoelectric applications. In this review, the relationship of perovskite structure modified is outlined by surface ligand and some properties on account of the ion structure features. This review specifically focuses on the roles of surface ligands in the construction of IHP NCs with fewer defects, higher PL QY, and better stability. Generally, ligands binding to the surface of IHP NCs can form passivation layer, which are beneficial to not only the improvement of PL QY by filling the Br− or Pb2+ vacancy but also the enhancement of stability. The surface passivation mechanisms are attributed to the [Br⋯HN+] hydrogen‐bonding, chelation, and dative covalent bond interactions. Furthermore, degradation mechanisms assigned to the hydration, ion migration, and dissociation are discussed. The equilibrium problem of purifying and QY and possible reasons are also addressed, which are believed to be solved in the near future with the help of coordination chemistry and surface engineering. Finally, a brief outlook including challenges and possible development is provided.

The challenges of developing neuromorphic vision systems inspired by the human eye come not only from how to recreate the flexibility, sophistication, and adaptability of animal systems, but also how to do so with computational efficiency and elegance. Similar to biological systems, these neuromorphic circuits integrate functions of image sensing, memory and processing into the device, and process continuous analog brightness signal in real-time. High-integration, flexibility and ultra-sensitivity are essential for practical artificial vision systems that attempt to emulate biological processing. Here, we present a flexible optoelectronic sensor array of 1024 pixels using a combination of carbon nanotubes and perovskite quantum dots as active materials for an efficient neuromorphic vision system. The device has an extraordinary sensitivity to light with a responsivity of 5.1 × 107 A/W and a specific detectivity of 2 × 1016 Jones, and demonstrates neuromorphic reinforcement learning by training the sensor array with a weak light pulse of 1 μW/cm2.