Morphology management for tailoring the properties of monolayer transition-metal dichalcogenides (TMDCs), that is, molybdenum disulfide (MoS), has attracted great interest for promising applications such as in electrocatalysis and optoelectronics. Nevertheless, little progress has been made in engineering the shape of MoS. Herein, we introduce a modified chemical vapor deposition method to grow monolayer MoS dendrites by pretreating substrates with adhesive tapes. The as-grown MoS crystals are featured with hexagonal backbones with fractal shapes and tunable degrees. By characterizing the atomic structure, it is found that these morphologies are mainly initiated from the twin defect derived growth and controlled by the S:Mo vapor ratio. Due to the accumulated sulfur vacancies in the cyclic twin regions, strong enhancement of photoluminescence emission is localized, which determines the shape dependency of optical property. This work not only enriches the understanding of the twin defects derived crystal growth mechanism and extends its applications from nanomaterials to two-dimensional crystals, but also offers a robust and controllable protocol for shape-engineered monolayer TMDCs in electrochemical and optoelectronic applications.

Ternary metal halides, including perovskites, have become a popular field of study over the last decade. Recently many groups have attempted to replace the lead in lead-based perovskites with other...

Quantum-confined CsPbI 3 nanocrystals (NCs) are promising materials for the next generation of pure-red displays. Small quantum dots synthesized by colloidal methods often have excess resistive ligands, which reduce the efficiency and long-term stability of the resulting light-emitting diodes (LEDs). Here we developed a facile ligand-exchange method using amino acids to reduce long chain ligands on CsPbI 3 quantum dots and improve the efficiency and stability of LEDs made from these QDs. We also assessed a variety of related amino acids and noted how their structure affects the LED performance. We found that a dual-passivation effect was observed in cysteinepassivated QDs that led to the best performance. The optimized LEDs achieved an external quantum efficiency (EQE) of 18.0% and a T 50 of 87 min, comparable with many of the best reported perovskite QD, pure red LEDs.

AgBiS2 nanocrystals are a promising nontoxic alternative to PbS, CsPbI3, and CdS quantum dots for solution-fabricated nanocrystal photovoltaics. In this work, we fabricated the first inverted (p–i–n) structure AgBiS2 nanocrystal solar cells. We selected spray-coated NiO as the hole-transporting material and used PCBM/BCP as the electron-transporting material. Combining transient photocurrent and photovoltage measurements with femtosecond transient absorption spectroscopy, we investigated the charge collection process on metal oxide/AgBiS2 interfaces and demonstrated that the NiO/AgBiS2 NC junction in the p–i–n configuration is more efficient for charge carrier collection. The fabricated p–i–n solar cells exhibited a 4.3% power conversion efficiency (PCE), which was higher than that of conventional n–i–p solar cells fabricated using the same sample. Additionally, inverted devices showed an ultrahigh short-circuit current (J SC) over 20.7 mA cm–2 and 0.38 V open-circuit voltage (V OC), suggesting their potential for further improvements in efficiency and, eventually, for large-scale production.

Flexible pressure sensors play an indispensable role in flexible electronics. Microstructures on flexible electrodes have been proven to be effective in improving the sensitivity of pressure sensors. However, it remains a challenge to develop such microstructured flexible electrodes in a convenient way. Inspired by splashed particles from laser processing, herein, a method for customizing microstructured flexible electrodes by femtosecond laser‐activated metal deposition is proposed. It takes advantage of the catalyzing particles scattered during femtosecond laser ablation and is particularly suitable for moldless, maskless, and low‐cost fabrication of microstructured metal layers on polydimethylsiloxane (PDMS). Robust bonding at the PDMS/Cu interface is evidenced by the scotch tape test and the duration test over 10 000 bending cycles. Benefiting from the firm interface, the developed flexible capacitive pressure sensor with microstructured electrodes presents several conspicuous features, including a sensitivity (0.22 kPa−1) 73 times higher than the one using flat Cu electrodes, ultralow detection limit (<1 Pa), rapid response/recovery time (4.2/5.3 ms), and excellent stability. Moreover, the proposed method, inheriting the merits of laser direct writing, is capable of fabricating a pressure sensor array in a maskless manner for spatial pressure mapping.

Semiconductor nanorods have often been observed to emit polarized light. This property can be useful for emission applications such as displays, optical communications, and biological labeling. Recently, many researchers have tried to replace nanocrystals containing toxic metals, such as Cd or Pb, with alternatives that can also demonstrate polarized emission. Here a low temperature injection (LTI) method with a relatively short chain octylammonium bromide ligand precursor is used to slow down the nanorod formation reaction and the controlled anisotropic growth of Cs3Cu2Br5 nanorods is realized, producing more uniform samples of nanorods with higher aspect ratios than those previously reported. Such nanorods exhibit a very high degree of polarization (DOP) of 0.88 ± 0.04 for single rods, and a corresponding polarization anisotropy of 0.26 for the sample population, both the highest yet reported for any perovskite‐like material. Further this method can be extended to produce Cs3Cu2Cl5 nanorods as well, allowing for broad tuning of their optical properties.

These devices use perovskites with an ABX 3 structure as the active emitting layer, where A is Cs, MA or FA, B is Pb or Sn, and X is the halides. In recent years, the EQE for this device type has surged from less than 1% to over 20% for green, red and infra-red peLEDs. [7][8][9][10] Blue LEDs are also needed for displays and lighting applications, but thus far have lagged in EQE, color stability and lifetime, despite recent advances. [1] Blue (460 -480 nm) or sky-blue (480 -500 nm) peLEDs can be achieved by two possible methods: halide tuning, by adding chloride into a bromide-based perovskite (e.g., CsPbBr 3 ), [11,12] and more recently, through the quantum confinement effect, using 0D nanocrystals (NCs) [13][14][15][16][17][18][19] or quasi-2D layered perovskites. For example, You et al. reported a blue peLED incorporating EA into the Cs + site in PEA 2 (CsPbBr 3 ) 2 PbBr 4 to form passivated 2D/3D perovskite devices showing a record high EQE of 12.1% at 488 nm. [20] A key challenge for blue peLEDs is overcoming the issue of spectral (color) instability, especially when a mixed halide strategy is used to achieve blue emitting films. These perovskites, whether in the form of bulk, [21] quasi-2D, [22] or 0D nanocrystals, [23,24] often suffer from unwanted phasesegregation under photo-or electrical excitation, [25][26][27] in which the emission peak can shift or multiple peaks are observed due to ion migration. [28] Efforts to achieve spectral stability in blue peLEDs include A-site cation alloying, [29] tailoring bulky cations, [30,31] passivation, [32] and interface engineering. [33] Additionally, metal doping has long been investigated as an effective approach for enhancing perovskite optoelectronic performance, and this work has extended to peLEDs as well. [32,[34][35][36] Hou et al. reported a nanocrystal peLED doped with Mn that emitted at 466 nm with an EQE of 2.12%. [13] Most recently, Wang et al. reported yttrium (III) chloride doped quaisi-2D CsPbBr 3 :PEACl showing EQE of 11.0% and a maximum brightness of 9040 cd m -2 in the sky-blue region (roughly 485 -500 nm). [37] In this work, we investigate the activity of divalent metal ions as passivation materials in PEA-based 2D/3D CsPbX 3 perovskites, where X is mixed Br and Cl. The above Perovskite light-emitting devices (peLEDs) have recently gained widespread attention as candidates for next-generation display technologies.Red and green peLEDs have achieved over 20% external quantum efficiency (EQE), however blue peLEDs still lag behind. One proposed solution for improving the performance of blue peLEDs has been doping the perovskite films with metal ions, ostensibly to passivate surface trap sites and improve the EQE. Despite a few recent reports, however, the many roles of the metal ion dopants have not yet been fully explored. Here improvements in the EQE and spectral stability of quasi-2D perovskites, often called 2D/3D or layered perovskites are reported. CsPbBr 3−x Cl x skyblue emitting peLEDs, with a maximum EQE of 7.5%, and color stable spectra at ...

Singlet fission is a process by which an organic semiconductor is able to generate two triplet excitons from a single photon. If charges from the triplets can be successfully harvested without heavy losses in energy, then this process can enable a single‐junction solar cell to surpass the Shockley–Queisser limit. While singlet fission processes are commonly observed in several materials, harvesting the resulting triplets is difficult and has been demonstrated with only a few transport materials. Here, transient absorption spectroscopy is used to investigate singlet fission and carrier transfer processes at the AgBiS2/pentacene (AgBiS2/Pc) heterojunction. The successful transfer of triplets from pentacene to AgBiS2 and the transfer of holes from AgBiS2 to pentacene is observed. Further singlet fission in pentacene by modifying the crystallinity of the pentacene layer and have fabricated the first singlet fission AgBiS2/Pc solar cell is enhanced. Singlet fission devices exhibit higher external quantum efficiency compared with the control devices, and thus demonstrating the significant contribution of charges from the singlet fission process.