High-Performance Blue Perovskite Light-Emitting Diodes Enabled by Synergistic Effect of Additives.

While quasi-two-dimensional (quasi-2D) perovskites have good properties of cascade energy transfer, high exciton binding energy, and high quantum efficiency, which will benefit high-efficiency blue PeLEDs, inefficient domain distribution management and unbalanced carrier transport impede device performance improvement. Herein, (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) and methyl 2-aminopyridine-4-carboxylate (MAC) were simultaneously introduced to a blue quasi-2D perovskite film. Relying on the synergistic effect of 2PACz and MAC, it not only modulates the phase distribution inhibiting the n = 2 phase but also greatly improves the electrical property of the quasi-2D perovskite film. As a result, the as-modified blue quasi-2D PeLED demonstrated an external quantum efficiency (EQE) of 17.08% and a luminance of 10142 cd m-2. This study exemplifies the synergistic effect among dual additives and offers a new effective additive strategy modulating phase distribution and building balanced carrier transport, which paves the way for the fabrication of highly efficient blue PeLEDs.

Multiple Phase Regulation Enables Efficient and Bright Quasi-2D Perovskite Light-Emitting Diodes.

Quasi-2D perovskites, multiquantum well materials with the energy cascade structure, exhibit impressive optoelectronic properties and a wide range of applications in various optoelectronic devices. However, the insufficient exciton energy transfer caused by the excess of small-n phases that induce nonradiative recombination and the spatially random phase distribution that impedes charge transport severely inhibit the device performance of light-emitting diodes (LEDs). Here, a faster energy transfer process and efficient carrier recombination are achieved by introducing the multifunctional additive 2-(methylsulfonyl)-4-(trifluoromethyl)benzoic acid (MTA) to manipulate the crystallization process of perovskites. The introduction of MTA not only constrains the PEA and restrains the formation of small-n phases to improve the energy transfer process but also optimizes the crystal orientation to promote charge transport. As a result, highly efficient pure green quasi-2D perovskite LEDs with a peak EQE of 25.9%, a peak current efficiency of 108.1 cd A-1, and a maximum luminance of 288798 cd m-2 are achieved.

Magnetic Field-Assisted Interface Embedding Strategy to Construct 2D/3D Composite Structure for Stable Perovskite Solar Cells with Efficiency Over 24.

Perovskite solar cells (PSCs) based on 2D/3D composite structure have shown enormous potential to combine high efficiency of 3D perovskite with high stability of 2D perovskite. However, there are still substantial non-radiative losses produced from trap states at grain boundaries or on the surface of conventional 2D/3D composite structure perovskite film, which limits device performance and stability. In this work, a multifunctional magnetic field-assisted interfacial embedding strategy is developed to construct 2D/3D composite structure. The composite structure not only improves crystallinity and passivates defects of perovskite layer, but also can efficiently promote vertical hole transport and provide lateral barrier effect. Meanwhile, the composite structure also forms a good surface and internal encapsulation of 3D perovskite to inhibit water diffusion. As a result, the multifunctional effect effectively improves open-circuit voltage and fill factor, reaching maximum values of 1.246 V and 81.36%, respectively, and finally achieves power conversion efficiency (PCE) of 24.21%. The unencapsulated devices also demonstrate highly improved long-term stability and humidity stability. Furthermore, an augmented performance of 21.23% is achieved, which is the highest PCE of flexible device based on 2D/3D composite perovskite films coupled with the best mechanical stability due to the 2D/3D alternating structure.

Halide Double Perovskite Nanocrystals Doped with Rare-Earth Ions for Multifunctional Applications.

Most lead-free halide double perovskite materials display low photoluminescence quantum yield (PLQY) due to the indirect bandgap or forbidden transition. Doping is an effective strategy to tailor the optical properties of materials. Herein, efficient blue-emitting Sb3+ -doped Cs2 NaInCl6 nanocrystals (NCs) are selected as host, rare-earth (RE) ions (Sm3+ , Eu3+ , Tb3+ , and Dy3+ ) are incorporated into the host, and excellent PLQY of 80.1% is obtained. Femtosecond transient absorption measurement found that RE ions not only served as the activator ions but also filled the deep vacancy defects. Anti-counterfeiting, optical thermometry, and white-light-emitting diodes (WLEDs) are exhibited using these RE ions-doped halide double perovskite NCs. For the optical thermometry based on Sm3+ -doped Cs2 NaInCl6 :Sb3+ NCs, the maximum relative sensitivity is 0.753% K-1 , which is higher than those of most temperature-sensing materials. Moreover, the WLED fabricated by Sm3+ -doped Cs2 NaInCl6 :Sb3+ NCs@PMMA displays CIE color coordinates of (0.30, 0.28), a luminous efficiency of 37.5 lm W-1 , a CCT of 8035 K, and a CRI over 80, which indicate that Sm3+ -doped Cs2 NaInCl6 :Sb3+ NCs are promising single-component white-light-emitting phosphors for next-generation lighting and display technologies.

A novel CO2 utilization technology for the synergistic co-production of multi-walled carbon nanotubes and syngas.

Dry reforming of methane (DRM) is a well-known process in which CH4 and CO2 catalytically react to produce syngas. Solid carbon is a well-known byproduct of the DRM but is undesirable as it leads to catalyst deactivation. However, converting CO2 and CH4 into solid carbon serves as a promising carbon capture and sequestration technique that has been demonstrated in this study by two patented processes. In the first process, known as CARGEN technology (CARbon GENerator), a novel concept of two reactors in series is developed that separately convert the greenhouse gases (GHGs) into multi-walled carbon nanotubes (MWCNTs) and syngas. CARGEN enables at least a 50% reduction in energy requirement with at least 65% CO2 conversion compared to the DRM process. The second process presents an alternative pathway for the regeneration/reactivation of the spent DRM/CARGEN catalyst using CO2. Provided herein is the first report on an experimental demonstration of a 'switching' technology in which CO2 is utilized in both the operation and the regeneration cycles and thus, finally contributing to the overall goal of CO2 fixation. The following studies support all the results in this work: physisorption, chemisorption, XRD, XPS, SEM, TEM, TGA, ICP, and Raman analysis.

Thermal Evolution of One-Dimensional Iodine Chains.

In one-dimensional (1D) systems, the definition of three common states of matter (solid, liquid, and gas) becomes obscure because it has been theoretically predicted that a 1D system has no phase transition. Due to technical difficulty in tracking 1D thermal evolution, hardly any experimental evidence has demonstrated whether there exist these three states. Here we report Raman experimental observation that 1D iodine molecular chains formed inside the nanosized channel undergo continuous transformation from chain structure to single molecules with increasing temperature, without having a sudden change as commonly observed in phase transition. At low temperatures, short-range order exists and manifests itself as long chains in structure, which gradually break into shorter chains with increasing temperature. The 1D system progressively gets more and more disordered, which is in agreement with the theoretical derivations. Our work may benefit the emerging molecular scale electronics.

Estimating atomic sizes with Raman spectroscopy.

We demonstrate a technique to determine the Van der Waals radius of iodine atoms using Raman spectroscopy. The iodine diatomic molecules are diffused into the nano-scale channels of a zeolite single crystal. We found their polarized Raman spectroscopy, which corresponds to iodine molecule's vibrational motion along the direction of molecular axis, is significantly modified by the interaction between the iodine molecules and the rigid frame of the crystal's nano-channels. From the number of excitable vibration quantum states of the confined iodine molecules determined from Raman spectra and the size of the nano-channels, we estimate the iodine atomic radius to be 2.10±0.05 Å. It is the first time that atomic sizes, which are far beyond the optical diffraction limit, have be resolved optically using Raman spectroscopy with the help of nano-scale structures.