Interfacial Heterojunction Enables High Efficient PbS Quantum Dot Solar Cells.

Colloidal quantum dots (CQDs) are promising optoelectronic materials for solution-processed thin film optoelectronic devices. However, the large surface area with abundant surface defects of CQDs and trap-assisted non-radiative recombination losses at the interface between CQDs and charge-transport layer limit their optoelectronic performance. To address this issue, an interface heterojunction strategy is proposed to protect the CQDs interface by incorporating a thin layer of polyethyleneimine (PEIE) to suppress trap-assisted non-radiative recombination losses. This thin layer not only acts as a protective barrier but also modulates carrier recombination and extraction dynamics by forming heterojunctions at the buried interface between CQDs and charge-transport layer, thereby enhancing the interface charge extraction efficiency. This enhancement is demonstrated by the shortened lifetime of carrier extraction from 0.72 to 0.46 ps. As a result, the resultant PbS CQD solar cells achieve a power-conversion-efficiency (PCE) of 13.4% compared to 12.2% without the heterojunction.

Kernel Bayesian nonlinear matrix factorization based on variational inference for human-virus protein-protein interaction prediction.

Identification of potential human-virus protein-protein interactions (PPIs) contributes to the understanding of the mechanisms of viral infection and to the development of antiviral drugs. Existing computational models often have more hyperparameters that need to be adjusted manually, which limits their computational efficiency and generalization ability. Based on this, this study proposes a kernel Bayesian logistic matrix decomposition model with automatic rank determination, VKBNMF, for the prediction of human-virus PPIs. VKBNMF introduces auxiliary information into the logistic matrix decomposition and sets the prior probabilities of the latent variables to build a Bayesian framework for automatic parameter search. In addition, we construct the variational inference framework of VKBNMF to ensure the solution efficiency. The experimental results show that for the scenarios of paired PPIs, VKBNMF achieves an average AUPR of 0.9101, 0.9316, 0.8727, and 0.9517 on the four benchmark datasets, respectively, and for the scenarios of new human (viral) proteins, VKBNMF still achieves a higher hit rate. The case study also further demonstrated that VKBNMF can be used as an effective tool for the prediction of human-virus PPIs.

Phosphorescent-Dye-Sensitized Quantum-Dot Light-Emitting Diodes with 37% External Quantum Efficiency.

Exciton harvesting is of paramount importance for quantum-dot light-emitting diodes (QLEDs). Direct exciton harvesting by the quantum dots (QDs) emitting layer suffers from poor hole injection due to the low conduction bands and valence bands of QDs, leading to unbalanced electron-hole injection and recombination. To address this issue, here, an exciton sensitizing approach is reported, where excitons form on a phosphorescent-dye-doped layer, which then transfer their energies to adjacent QDs layer for photon emission. Due to the very efficient exciton formation and energy-transfer processes, higher device performance can be achieved. To demonstrate the above strategy, red QLEDs with a phosphorescent dye, iridium (III) bis(2-methyldibenzo-[f,h]quinoxaline) (acetylacetonate), Ir(MDQ)2 (acac), doped hole-transporting layer are fabricated and studied. At a doping concentration of 10 wt%, the best device achieves record high current efficiency, power efficiency, and external quantum efficiency (EQE) of 37.3 cd A-1 , 41 lm W-1 , and 37%, respectively. Simultaneously, the efficiency roll-off characteristic is greatly improved, in that 35% EQE can be well retained at a high luminance level of 450 000 cd m-2 . Moreover, the devices also exhibit good stability and reproducibility.

Metabolite-disease interaction prediction based on logistic matrix factorization and local neighborhood constraints.

Background: Increasing evidence indicates that metabolites are closely related to human diseases. Identifying disease-related metabolites is especially important for the diagnosis and treatment of disease. Previous works have mainly focused on the global topological information of metabolite and disease similarity networks. However, the local tiny structure of metabolites and diseases may have been ignored, leading to insufficiency and inaccuracy in the latent metabolite-disease interaction mining. Methods: To solve the aforementioned problem, we propose a novel metabolite-disease interaction prediction method with logical matrix factorization and local nearest neighbor constraints (LMFLNC). First, the algorithm constructs metabolite-metabolite and disease-disease similarity networks by integrating multi-source heterogeneous microbiome data. Then, the local spectral matrices based on these two networks are established and used as the input of the model, together with the known metabolite-disease interaction network. Finally, the probability of metabolite-disease interaction is calculated according to the learned latent representations of metabolites and diseases. Results: Extensive experiments on the metabolite-disease interaction data were conducted. The results show that the proposed LMFLNC method outperformed the second-best algorithm by 5.28 and 5.61% in the AUPR and F1, respectively. The LMFLNC method also exhibited several potential metabolite-disease interactions, such as "Cortisol" (HMDB0000063), relating to "21-Hydroxylase deficiency," and "3-Hydroxybutyric acid" (HMDB0000011) and "Acetoacetic acid" (HMDB0000060), both relating to "3-Hydroxy-3-methylglutaryl-CoA lyase deficiency." Conclusion: The proposed LMFLNC method can well preserve the geometrical structure of original data and can thus effectively predict the underlying associations between metabolites and diseases. The experimental results show its effectiveness in metabolite-disease interaction prediction.

Light-emitting field-effect transistors with EQE over 20% enabled by a dielectric-quantum dots-dielectric sandwich structure.

Emerging quantum dots (QDs) based light-emitting field-effect transistors (QLEFETs) could generate light emission with high color purity and provide facile route to tune optoelectronic properties at a low fabrication cost. Considerable efforts have been devoted to designing device structure and to understanding the underlying physics, yet the overall performance of QLEFETs remains low due to the charge/exciton loss at the interface and the large band offset of a QD layer with respect to the adjacent carrier transport layers. Here, we report highly efficient QLEFETs with an external quantum efficiency (EQE) of over 20% by employing a dielectric-QDs-dielectric (DQD) sandwich structure. Such DQD structure is used to control the carrier behavior by modulating energy band alignment, thus shifting the exciton recombination zone into the emissive layer. Also, enhanced radiative recombination is achieved by preventing the exciton loss due to presence of surface traps and the luminescence quenching induced by interfacial charge transfer. The DQD sandwiched design presents a new concept to improve the electroluminescence performance of QLEFETs, which can be transferred to other material systems and hence can facilitate exploitation of QDs in a new type of optoelectronic devices.

Efficient Tandem Quantum-Dot LEDs Enabled by An Inorganic Semiconductor-Metal-Dielectric Interconnecting Layer Stack.

Light-emitting diodes (LEDs) in a tandem configuration offer a strategy to realize high-performance, multicolor devices. Until now, though, the efficiency of tandem colloidal quantum dot LEDs (QLEDs) has been limited due to unpassivated interfaces and solvent damage originating from the materials processing requirements of interconnecting layers (ICLs). Here an ICL is reported consisting of a semiconductor-metal-dielectric stack that provides facile fabrication, materials stability, and good optoelectronic coupling. It is investigated experimentally how the ICL enables charge balance, suppresses current leakage, and prevents solvent damage to the underlying layers. As a result record efficiencies are reported for double-junction tandem QLEDs, whose emission wavelengths cover from blue to red light; i.e., external quantum efficiencies (EQEs) of 40% (average 37+/-2%) for red, 49% (average 45+/-2%) for yellow, 50% (average 46+/-2%) for green, and 24% (average 21+/-2%) for blue are achieved.

Heterogeneous Supersaturation in Mixed Perovskites.

Thin-film solar cells based on hybrid lead halide perovskites have achieved certified power conversion efficiencies exceeding 24%, approaching those of crystalline silicon. This motivates deeper studies of the mechanisms that determine their performance. Twin defect sites have been proposed as a source of traps in perovskites, yet their origin and influence on photovoltaic performance remain unclear. It is found that twin defects-observed herein via both transmission electron microscopy and X-ray diffraction-are correlated with the amount of antisolvent added to the perovskite and that twin defects in the highest-performing perovskite photovoltaics are suppressed. Heterogeneous supersaturation nucleation is discussed as a contributor to efficient perovskite-based optoelectronic devices.

Combining Efficiency and Stability in Mixed Tin-Lead Perovskite Solar Cells by Capping Grains with an Ultrathin 2D Layer.

The development of narrow-bandgap (Eg ≈ 1.2 eV) mixed tin-lead (Sn-Pb) halide perovskites enables all-perovskite tandem solar cells. Whereas pure-lead halide perovskite solar cells (PSCs) have advanced simultaneously in efficiency and stability, achieving this crucial combination remains a challenge in Sn-Pb PSCs. Here, Sn-Pb perovskite grains are anchored with ultrathin layered perovskites to overcome the efficiency-stability tradeoff. Defect passivation is achieved both on the perovskite film surface and at grain boundaries, an approach implemented by directly introducing phenethylammonium ligands in the antisolvent. This improves device operational stability and also avoids the excess formation of layered perovskites that would otherwise hinder charge transport. Sn-Pb PSCs with fill factors of 79% and a certified power conversion efficiency (PCE) of 18.95% are reported-among the highest for Sn-Pb PSCs. Using this approach, a 200-fold enhancement in device operating lifetime is achieved relative to the nonpassivated Sn-Pb PSCs under full AM1.5G illumination, and a 200 h diurnal operating time without efficiency drop is achieved under filtered AM1.5G illumination.

Edge stabilization in reduced-dimensional perovskites.

Reduced-dimensional perovskites are attractive light-emitting materials due to their efficient luminescence, color purity, tunable bandgap, and structural diversity. A major limitation in perovskite light-emitting diodes is their limited operational stability. Here we demonstrate that rapid photodegradation arises from edge-initiated photooxidation, wherein oxidative attack is powered by photogenerated and electrically-injected carriers that diffuse to the nanoplatelet edges and produce superoxide. We report an edge-stabilization strategy wherein phosphine oxides passivate unsaturated lead sites during perovskite crystallization. With this approach, we synthesize reduced-dimensional perovskites that exhibit 97 ± 3% photoluminescence quantum yields and stabilities that exceed 300 h upon continuous illumination in an air ambient. We achieve green-emitting devices with a peak external quantum efficiency (EQE) of 14% at 1000 cd m-2; their maximum luminance is 4.5 × 104 cd m-2 (corresponding to an EQE of 5%); and, at 4000 cd m-2, they achieve an operational half-lifetime of 3.5 h.

In Situ Back-Contact Passivation Improves Photovoltage and Fill Factor in Perovskite Solar Cells.

Organic-inorganic hybrid perovskite solar cells (PSCs) have seen a rapid rise in power conversion efficiencies in recent years; however, they still suffer from interfacial recombination and charge extraction losses at interfaces between the perovskite absorber and the charge-transport layers. Here, in situ back-contact passivation (BCP) that reduces interfacial and extraction losses between the perovskite absorber and the hole transport layer (HTL) is reported. A thin layer of nondoped semiconducting polymer at the perovskite/HTL interface is introduced and it is shown that the use of the semiconductor polymer permits-in contrast with previously studied insulator-based passivants-the use of a relatively thick passivating layer. It is shown that a flat-band alignment between the perovskite and polymer passivation layers achieves a high photovoltage and fill factor: the resultant BCP enables a photovoltage of 1.15 V and a fill factor of 83% in 1.53 eV bandgap PSCs, leading to an efficiency of 21.6% in planar solar cells.

Color-stable highly luminescent sky-blue perovskite light-emitting diodes.

Perovskite light-emitting diodes (PeLEDs) have shown excellent performance in the green and near-infrared spectral regions, with high color purity, efficiency, and brightness. In order to shift the emission wavelength to the blue, compositional engineering (anion mixing) and quantum-confinement engineering (reduced-dimensionality) have been employed. Unfortunately, LED emission profiles shift with increasing driving voltages due to either phase separation or the coexistence of multiple crystal domains. Here we report color-stable sky-blue PeLEDs achieved by enhancing the phase monodispersity of quasi-2D perovskite thin films. We selected cation combinations that modulate the crystallization and layer thickness distribution of the domains. The perovskite films show a record photoluminescence quantum yield of 88% at 477 nm. The corresponding PeLEDs exhibit stable sky-blue emission under high operation voltages. A maximum luminance of 2480 cd m-2 at 490 nm is achieved, fully one order of magnitude higher than the previous record for quasi-2D blue PeLEDs.

Activated Electron-Transport Layers for Infrared Quantum Dot Optoelectronics.

Photovoltaic (PV) materials such as perovskites and silicon are generally unabsorptive at wavelengths longer than 1100 nm, leaving a significant portion of the IR solar spectrum unharvested. Small-bandgap colloidal quantum dots (CQDs) are a promising platform to offer tandem complementary IR PV solutions. Today, the best performing CQD PVs use zinc oxide (ZnO) as an electron-transport layer. However, these electrodes require ultraviolet (UV)-light activation to overcome the low carrier density of ZnO, precluding the realization of CQD tandem photovoltaics. Here, a new sol-gel UV-free electrode based on Al/Cl hybrid doping of ZnO (CAZO) is developed. Al heterovalent doping provides a strong n-type character while Cl surface passivation leads to a more favorable band alignment for electron extraction. CAZO CQD IR solar cell devices exhibit, at wavelengths beyond the Si bandgap, an external quantum efficiency of 73%, leading to an additional 0.92% IR power conversion efficiency without UV activation. Conventional ZnO devices, on the other hand, add fewer than 0.01 power points at these operating conditions.

Chemically Addressable Perovskite Nanocrystals for Light-Emitting Applications.

Whereas organic-inorganic hybrid perovskite nanocrystals (PNCs) have remarkable potential in the development of optoelectronic materials, their relatively poor chemical and colloidal stability undermines their performance in optoelectronic devices. Herein, this issue is addressed by passivating PNCs with a class of chemically addressable ligands. The robust ligands effectively protect the PNC surfaces, enhance PNC solution processability, and can be chemically addressed by thermally induced crosslinking or radical-induced polymerization. This thin polymer shield further enhances the photoluminescence quantum yields by removing surface trap states. Crosslinked methylammonium lead bromide (MAPbBr3 ) PNCs are applied as active materials to build light-emitting diodes that have low turn-on voltages and achieve a record luminance of over 7000 cd m-2 , around threefold better than previous reported MA-based PNC devices. These results indicate the great potential of this ligand passivation approach for long lifespan, highly efficient PNC light emitters.

Tailoring the Energy Landscape in Quasi-2D Halide Perovskites Enables Efficient Green-Light Emission.

Organo-metal halide perovskites are a promising platform for optoelectronic applications in view of their excellent charge-transport and bandgap tunability. However, their low photoluminescence quantum efficiencies, especially in low-excitation regimes, limit their efficiency for light emission. Consequently, perovskite light-emitting devices are operated under high injection, a regime under which the materials have so far been unstable. Here we show that, by concentrating photoexcited states into a small subpopulation of radiative domains, one can achieve a high quantum yield, even at low excitation intensities. We tailor the composition of quasi-2D perovskites to direct the energy transfer into the lowest-bandgap minority phase and to do so faster than it is lost to nonradiative centers. The new material exhibits 60% photoluminescence quantum yield at excitation intensities as low as 1.8 mW/cm2, yielding a ratio of quantum yield to excitation intensity of 0.3 cm2/mW; this represents a decrease of 2 orders of magnitude in the excitation power required to reach high efficiency compared with the best prior reports. Using this strategy, we report light-emitting diodes with external quantum efficiencies of 7.4% and a high luminescence of 8400 cd/m2.

Efficient and stable solution-processed planar perovskite solar cells via contact passivation.

Planar perovskite solar cells (PSCs) made entirely via solution processing at low temperatures (<150°C) offer promise for simple manufacturing, compatibility with flexible substrates, and perovskite-based tandem devices. However, these PSCs require an electron-selective layer that performs well with similar processing. We report a contact-passivation strategy using chlorine-capped TiO2 colloidal nanocrystal film that mitigates interfacial recombination and improves interface binding in low-temperature planar solar cells. We fabricated solar cells with certified efficiencies of 20.1 and 19.5% for active areas of 0.049 and 1.1 square centimeters, respectively, achieved via low-temperature solution processing. Solar cells with efficiency greater than 20% retained 90% (97% after dark recovery) of their initial performance after 500 hours of continuous room-temperature operation at their maximum power point under 1-sun illumination (where 1 sun is defined as the standard illumination at AM1.5, or 1 kilowatt/square meter).

Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering.

A two-step ligand-exchange strategy is developed, in which the long-carbon- chain ligands on all-inorganic perovskite (CsPbX3 , X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-pair-capped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs.

Perovskite energy funnels for efficient light-emitting diodes.

Organometal halide perovskites exhibit large bulk crystal domain sizes, rare traps, excellent mobilities and carriers that are free at room temperature-properties that support their excellent performance in charge-separating devices. In devices that rely on the forward injection of electrons and holes, such as light-emitting diodes (LEDs), excellent mobilities contribute to the efficient capture of non-equilibrium charge carriers by rare non-radiative centres. Moreover, the lack of bound excitons weakens the competition of desired radiative (over undesired non-radiative) recombination. Here we report a perovskite mixed material comprising a series of differently quantum-size-tuned grains that funnels photoexcitations to the lowest-bandgap light-emitter in the mixture. The materials function as charge carrier concentrators, ensuring that radiative recombination successfully outcompetes trapping and hence non-radiative recombination. We use the new material to build devices that exhibit an external quantum efficiency (EQE) of 8.8% and a radiance of 80 W sr-1 m-2. These represent the brightest and most efficient solution-processed near-infrared LEDs to date.

Organic semiconductor heterojunctions: electrode-independent charge injectors for high-performance organic light-emitting diodes.

Organic light-emitting diodes (OLEDs) are driven by injected charges from an anode and a cathode. The low and high work function metals are necessary for the effective injection of electrons and holes, respectively. Here, we introduce a fully novel design concept using organic semiconductor heterojunctions (OSHJs) as the charge injectors for achieving highly efficient OLEDs, regardless of the work functions of the electrodes. In contrast to traditional injected charges from the electrodes, the injected charges originate from the OSHJs. The device performance was shown to be significantly improved in efficiency and stability compared to conventional OLEDs. Attractively, the OLEDs based on OSHJs as charge injectors still exhibited an impressive performance when the low work function Al was replaced by air- and chemistry-stable high work function metals, such as Au, Ag, and Cu, as the cathode contact, which has been suggested to be difficult in conventional OLEDs. This concept challenges the conventional design approach for the injection of charges and allows for the realization of practical applications of OLEDs with respect to high efficiency, selectable electrodes, and a long lifetime.

Carbon Nanotube Driver Circuit for 6 × 6 Organic Light Emitting Diode Display.

Single-walled carbon nanotube (SWNT) is expected to be a very promising material for flexible and transparent driver circuits for active matrix organic light emitting diode (AM OLED) displays due to its high field-effect mobility, excellent current carrying capacity, optical transparency and mechanical flexibility. Although there have been several publications about SWNT driver circuits, none of them have shown static and dynamic images with the AM OLED displays. Here we report on the first successful chemical vapor deposition (CVD)-grown SWNT network thin film transistor (TFT) driver circuits for static and dynamic AM OLED displays with 6 × 6 pixels. The high device mobility of ~45 cm(2)V(-1)s(-1) and the high channel current on/off ratio of ~10(5) of the SWNT-TFTs fully guarantee the control capability to the OLED pixels. Our results suggest that SWNT-TFTs are promising backplane building blocks for future OLED displays.

Synthesis, physical properties, and light-emitting diode performance of phenazine-based derivatives with three, five, and nine fused six-membered rings.

Realizing the control of emission colors of single molecules is very important in the development of full-color emitting materials. Herein, three novel phenazine derivatives (2,3,7,8-tetrakis(decyloxy)phenazine (2a), 2,3-didecyloxy-5,14-diaza-7,12-dioxo-9,10- dicyanopentacene (2b), and 2,3,13,14-tetradecyloxy-5,11,16,22-tetraaza-7,9,18,20-tetraoxo-8,19-dicyanoenneacene (2c)) have been successfully synthesized and fully characterized. Compound 2c can emit blue light in toluene solution (450 nm), green light in the powder/film state (502/562 nm), and red light in the 2c/TFA state (610 nm). The OLED with 2c emits a strong green light at a peak of 536 nm with a maximum luminance of the OLED of about 8600 cd m(-2), which indicates that 2c could be a promising fluorescent dye for OLED applications.