Phosphomolybdic Acid-Modified Monolayer Graphene Anode for Efficient Organic and Perovskite Light-Emitting Diodes

MoS2-Based Nanocomposites for Photocatalytic Hydrogen Evolution and Carbon Dioxide Reduction

Photocatalysis is a facile and sustainable approach for energy conversion and environmental remediation by generating solar fuels from water splitting. Due to their two-dimensional (2D) layered structure and excellent physicochemical properties, molybdenum disulfide (MoS₂) has been effectively utilized in photocatalytic H₂ evolution reaction (HER) and CO₂ reduction. The photocatalytic efficiency of MoS₂ greatly depends on the active edge sites present in their layered structure. Modifications like reducing the layer numbers, creating defective structures, and adopting different morphologies produce more unsaturated S atoms as active edge sites. Hence, MoS₂ acts as a cocatalyst in nanocomposites/heterojunctions to facilitate the photogenerated electron transfer. This review highlights the role of MoS₂ as a cocatalyst for nanocomposites in H₂ evolution reaction and CO₂ reduction. The H₂ evolution activity has been described comprehensively as binary (with metal oxide, carbonaceous materials, metal sulfides, and metal-organic frameworks) and ternary composites of MoS₂. Photocatalytic CO₂ reduction is a more complex and challenging process that demands an efficient light-responsive semiconductor catalyst to tackle the thermodynamic and kinetic factors. Photocatalytic reduction of CO₂ using MoS₂ is an emerging topic and would be a cost-effective substitute for noble catalysts. Herein, we also exclusively envisioned the possibility of layered MoS₂ and its composites in this area. This review is expected to furnish an understanding of the diverse roles of MoS₂ in solar fuel generation, thus endorsing an interest in utilizing this unique layered structure to create nanostructures for future energy applications.

Conductivity and Stability Enhancement of PEDOT:PSS Electrodes via Facile Doping of Sodium 3-Methylsalicylate for Highly Efficient Flexible Organic Light-Emitting Diodes

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most prospering transparent conductive materials for flexible optoelectronic devices, which arises from its nonpareil features of low-cost solution processability, tunable conductivity, high transparency, and superior mechanical flexibility. However, acidity and hygroscopicity of PSS chains cause a decrease in conductivity, substrate corrosion, and device degradation. This work proposes a facile and effective direct doping strategy of sodium 3-methylsalicylate to enhance the conductivity, alleviate the acidity, and improve the stability of PEDOT:PSS electrodes, simultaneously. Owing to the formation of weaker acid and PSS-Na, PSS chains are disentangled from the coiled PEDOT:PSS complexes, leading to the phase separation of PEDOT:PSS and the formation of fibril-like PEDOT domains. Eventually, the sodium 3-methylsalicylate-modified PEDOT:PSS electrode is employed in flexible organic light-emitting diodes with an outstanding external quantum efficiency of up to 25%. The improved performance is attributed to the more matched work function and the as-formed interfacial dipole. The sodium 3-methylsalicylate-modified PEDOT:PSS electrode with high conductivity and transmittance, superior stability in the air as well as good mechanical flexibility has the potential to be the most promising transparent conductive material for flexible optoelectronic device applications.

Stable and Efficient Red Perovskite Light-Emitting Diodes Based on Ca2+-Doped CsPbI3 Nanocrystals

α-CsPbI₃ nanocrystals (NCs) with poor stability prevent their wide applications in optoelectronic fields. Ca²⁺ (1.00 Å) as a new B-site doping ion can successfully boost CsPbI₃ NC performance with both improved phase stability and optoelectronic properties. With a Ca²⁺/Pb²⁺ ratio of 0.40%, both phase and photoluminescence (PL) stability could be greatly enhanced. Facilitated by increased tolerance factor, the cubic phase of its solid film could be maintained after 58 days in ambient condition or 4 h accelerated aging process at 120°C. The PL stability of its solution could be preserved to 83% after 147 days in ambient condition. Even using UV light to accelerate aging, the T₅₀ of PL could boost 1.8-folds as compared to CsPbI₃ NCs. Because Ca²⁺ doping can dramatically decrease defect densities of films and reduce hole injection barriers, the red light-emitting diodes (LEDs) exhibited about triple enhancement for maximum the external quantum efficiency (EQE) up to 7.8% and 2.2 times enhancement for half-lifetime of LED up to 85 min. We believe it is promising to further explore high-quality CsPbI₃ NC LEDs via a Ca²⁺-doping strategy.