Thiophene-Diketopyrrolopyrrole-Based Quinoidal Small Molecules as Solution-Processable and Air-Stable Organic Semiconductors: Tuning of the Length and Branching Position of the Alkyl Side Chain toward a High-Performance n‑Channel Organic Field-Effect Transistor

A series of thiophene-diketopyrrolopyrrole-based quinoidal small molecules (<b>TDPPQ-2</b>–<b>TDPPQ-5</b>) bearing branched alkyl chains with different side-chain lengths and varied branching positions are synthesized. Field-effect transistor (FET) measurement combined with thin-film characterization is utilized to systematically probe the influence of the side-chain length and branching position on the film microstructure, molecular packing, and, hence, charge-transport property. All of these <b>TDPPQ</b> derivatives show air-stable n-channel transporting behavior in spin-coated FET devices, which exhibit no significant decrease in mobility even after being stored in air for 2 months. Most notably, <b>TDPPQ-3</b> exhibits an outstanding n-channel semiconducting property with electron mobilities up to 0.72 cm² V^–1 s^–1, which is an unprecedented value for spin-coated DPP-based n-type semiconducting small molecules. A balance of high crystallinity, satisfactory thickness uniformity and continuity, and strong intermolecular interaction accounts for the superior charge-transport characteristics of <b>TDPPQ-3</b> films. Our study demonstrates that tuning the length and branching position of alkyl side chains of semiconducting molecules is a powerful strategy for achieving high FET performance

Achieving High-Performance Solution-Processed Orange OLEDs with the Phosphorescent Cyclometalated Trinuclear Pt(II) Complex

Cyclometalated Pt­(II) complexes can show intense phosphorescence at room temperature. Their emission properties are determined by both the organic ligand and the metal center. Whereas most of the related studies focus on tuning the properties by designing different types of organic ligands, only several reports investigate the key role played by the metal center. To address this issue, phosphorescent Pt­(II) complexes with one, two, and three Pt­(II) centers are designed and synthesized. With more Pt­(II) centers, the cyclometalated multinuclear Pt­(II) complexes display red-shifted emissions with increased photoluminescence quantum yields. Most importantly, solution-processed organic light-emitting diodes (OLEDs) with the conventional device structure using the multinuclear Pt­(II) complexes as emitters show excellent performance. The controlled device based on the conventional mononuclear Pt­(II) complex shows a peak external quantum efficiency, current efficiency, and power efficiency of 6.4%, 14.4 cd A^–1, and 12.1 lm W^–1, respectively. The efficiencies are dramatically improved to 10.5%, 21.4 cd A^–1, and 12.9 lm W^–1 for the OLED based on the dinuclear Pt­(II) complex and to 17.0%, 35.4 cd A^–1, and 27.2 lm W^–1 for the OLED based on the trinuclear Pt­(II) complex, respectively. To the best of our knowledge, these efficiencies are among the highest ever reported for the multinuclear Pt­(II) complex-based OLEDs

Nanoporous Sulfur-Doped Copper Oxide (Cu₂O_<i>x</i>S_1–<i>x</i>) for Overall Water Splitting

Developing active and bifunctional noble metal-free electrocatalysts is crucial for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in the full water splitting process. A ternary nanoporous sulfur-doped copper oxide (Cu₂O_<i>x</i>S_1–<i>x</i>) was successfully synthesized on Cu foam. The obtained Cu₂O_<i>x</i>S_1–<i>x</i>/Cu shows robust electrocatalytic activity toward HER with a low overpotential of 40 mV at 10 mA cm^–2 and a Tafel slope of 68 mV dec^–1 and exhibits long-term stability in acid solution. Moreover, Cu₂O_<i>x</i>S_1–<i>x</i> shows excellent electrocatalytic activity for OER, HER, and overall water splitting as a bifunctional catalyst in 1.0 M KOH electrolyte. The sulfur doping strategy implemented here can greatly improve the catalytic performance and stability in both acidic and alkaline water electrolyzers and presents an efficient catalyst for overall water splitting

High-Index Faceted Ni₃S₂ Nanosheet Arrays as Highly Active and Ultrastable Electrocatalysts for Water Splitting

Elaborate design of highly active and stable catalysts from Earth-abundant elements has great potential to produce materials that can replace the noble-metal-based catalysts commonly used in a range of useful (electro)­chemical processes. Here we report, for the first time, a synthetic method that leads to <i>in situ</i> growth of {2̅10} high-index faceted Ni₃S₂ nanosheet arrays on nickel foam (NF). We show that the resulting material, denoted Ni₃S₂/NF, can serve as a highly active, binder-free, bifunctional electro­catalyst for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Ni₃S₂/NF is found to give ∼100% Faradaic yield toward both HER and OER and to show remarkable catalytic stability (for >200 h). Experimental results and theoretical calculations indicate that Ni₃S₂/NF’s excellent catalytic activity is mainly due to the synergistic catalytic effects produced in it by its nanosheet arrays and exposed {2̅10} high-index facets