High efficiency blue organic light-emitting diodes with below-bandgap electroluminescence

Blue organic light-emitting diodes require high triplet interlayer materials, which induce large energetic barriers at the interfaces resulting in high device voltages and reduced efficiencies. Here, we alleviate this issue by designing a low triplet energy hole transporting interlayer with high mobility, combined with an interface exciplex that confines excitons at the emissive layer/electron transporting material interface. As a result, blue thermally activated delay fluorescent organic light emitting diodes with a below-bandgap turn-on voltage of 2.5 V and an external quantum efficiency of 41.2% were successfully fabricated. These devices also showed suppressed efficiency roll-off maintaining an EQE of 34.8% at 1000 cd m-2. Our approach paves the way for further progress through exploring alternative device engineering approaches instead of only focusing on the demanding synthesis of organic compounds with complex structures

Influence of electrolyte co-additives on the performance of dye-sensitized solar cells

The presence of specific chemical additives in the redox electrolyte results in an efficient increase of the photovoltaic performance of dye-sensitized solar cells (DSCs). The most effective additives are 4-tert-butylpyridine (TBP), N-methylbenzimidazole (NMBI) and guanidinium thiocyanate (GuNCS) that are adsorbed onto the photoelectrode/electrolyte interface, thus shifting the semiconductor's conduction band edge and preventing recombination with triiodides. In a comparative work, we investigated in detail the action of TBP and NMBI additives in ionic liquid-based redox electrolytes with varying iodine concentrations, in order to extract the optimum additive/I2 ratio for each system. Different optimum additive/I2 ratios were determined for TBP and NMBI, despite the fact that both generally work in a similar way. Further addition of GuNCS in the optimized electrolytic media causes significant synergistic effects, the action of GuNCS being strongly influenced by the nature of the corresponding co-additive. Under the best operation conditions, power conversion efficiencies as high as 8% were obtained

Open-cage fullerene derivatives with 15-membered-ring orifices.

The addition reaction of the N-MEM-ketolactam derivative of [60]fullerene with phenyl, p-Br-phenyl, and p-MeO-phenyl hydrazines proceeds regioselectively, affording three open-cage fullerene derivatives bearing a 15-membered-ring orifice on the fullerene cage. Both experimental data and theoretical calculations were utilized for the structure determination of the new [60]fullerene adducts

Open-cage fullerene derivatives with 15-membered-ring orifices.

The addition reaction of the N-MEM-ketolactam derivative of [60]fullerene with phenyl, p-Br-phenyl, and p-MeO-phenyl hydrazines proceeds regioselectively, affording three open-cage fullerene derivatives bearing a 15-membered-ring orifice on the fullerene cage. Both experimental data and theoretical calculations were utilized for the structure determination of the new [60]fullerene adducts

A three-step healing approach for high performance n-channel perovskite transistors and logical circuits

This is the author accepted manuscript.Data availability: The data that support the findings of this study are available from the corresponding authors upon reasonable request.Code availability statement: All codes (software) used in the calculation and visualization are publicly available and the condition of their usage in publication is an appropriate citation.Progress in all-inorganic tin halide perovskites has recently enabled the fabrication of p-channel transistors with mobilities exceeding 50 cm2 V-1 s-1. However, the performance of the n-channel counterparts is currently limited to 4 cm2 V-1 s-1, undermining efforts to realize all-perovskite logical circuits. Herein, we report n-channel hysteresis-free perovskite transistors with electron mobilities of 25.15 cm2 V−1 s−1 combined with exceptional stability upon continuous bias stress. This is achieved through the application of a rational three-step healing approach, consisting of: (i) the addition of methyl ammonium chloride to stabilize the alpha-phase of formamidinium lead iodide; (ii) dilution with tetrahydrofuran to substantially improve the morphology of the perovskite channel; and (iii) surface treatment with tetramethylammonium hexafluorophosphate to further reduce the concentration of ionic bulk and surface defects. Upon applying a short post-annealing of the surface modifier, an unprecedented mobility of 33 cm2 V−1 s−1 is further attained. These transistors are integrated to fabricate unipolar inverters and eleven-stage ring oscillators, paving the path towards all-perovskite logical circuits.Korea Research Foundatio

Synthesis of N-heterocyclic carbene ligands and derived ruthenium olefin metathesis catalysts

We describe the synthesis of commonly used free N-heterocyclic carbenes (NHCs), 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr), and of the two corresponding ruthenium-based metathesis complexes. The complex containing IMes was found to be highly efficient in macrocyclizations involving ring-closing metatheses (RCM), whereas the complex featuring the IPr ligand shows excellent activity in both RCM and cross metathesis because of its greater stability. The free carbenes IMes and IPr are isolated in four steps, with an overall yield of similar to 50%. They are then used to replace a labile phosphine in precatalysts belonging to two families of ruthenium-containing complexes, benzylidene and indenylidene types, respectively. Such complexes are isolated as analytically pure compounds with 77% and 95% yield. The total time for the synthesis of the free NHCs is 56 h, and incorporation in complexes requires an additional 4-5 h.</p