CZTS Decorated on Graphene Oxide as an Efficient Electrocatalyst for High-Performance Hydrogen Evolution Reaction

Cu2ZnSnS4 (CZTS) was synthesized by the sonochemical method using 2-methoxyethanol as the solvent and subsequently decorated onto graphene oxide (GO synthesized by the modified Hummers' method) using two different approaches such as in situ growth and ex situ synthesis followed by deposition. Preliminary characterizations indicated that the synthesized CZTS belongs to the kesterite structure with a sphere-like morphology. The in situ-synthesized CZTS/GO (I-CZTS/GO) composite is used as an efficient electrocatalyst for hydrogen evolution reaction (HER) which revealed superior electrocatalytic activity with a reduced overpotential (39.3 mV at 2 mA cm-2), Tafel slope (70 mV dec-1), a larger exchange current density of 908 mA cm-2, and charge transfer resistance (5 Ω), significantly different from pure CZTS. Besides, the I-CZTS/GO composite exhibits highest HER performance with high current stability of which shows no noticeable degradation after i-t amperometry. The catalytic activity demonstrates that the I-CZTS/GO composite could be a promising electrocatalyst in hydrogen production from their cooperative interactions.

High-performance inverted organic light-emitting diodes with extremely low efficiency roll-off using solution-processed ZnS quantum dots as the electron injection layer

The electron-injecting layer (EIL) is one of the key factors in inverted organic light-emitting diodes (OLEDs) to realize high electroluminescence efficiency. Here, we proposed a novel cathode-modified EIL based on ZnS quantum dots (QDs) in inverted OLEDs, and demonstrated that the device performance was dramatically improved compared to traditional ZnO EIL. The EIL of ZnS QDs may greatly promote the electron injection ability and consequently increase the charge carrier recombination efficiency for the device. We also investigated the effects of different pH values (ZnS-A, pH = 10; ZnS-B, pH = 12) on the properties of ZnS QDs. The best inverted phosphorescent OLED device employing mCP:Ir(ppy)₃ as the emission layer showed a low turn-on voltage of 2.9 V and maximum current efficiency of 61.5 cd A⁻¹. Also, the ZnS-A based device exhibits very-low efficiency roll-off of 0.9% and 4.3% at 1000 cd m⁻² and 5000 cd m⁻², respectively. Our results indicate that use of ZnS QDs is a promising strategy to increase the performance in inverted OLEDs.

The electron-injecting layer (EIL) is one of the key factors in inverted organic light-emitting diodes (OLEDs) to realize high electroluminescence efficiency.

Lasing and Transport Properties of Poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)] (POFP) for the Application of Diode-Pumped Organic Solid Lasers

This paper demonstrates the lasing and transport properties of a green conjugated polymer, namely POFP. High photoluminescence yields and excellent electron transport of POFP film make it promising for gain media. Low threshold value of 4.0 μJ/cm² for amplified spontaneous emissions under a pulsed Nd:YAG laser at 355 nm was obtained, as well as a high Q-factor of 159. An inverted waveguide microcavity scheme has been developed to fabricate diode-pumped organic solid lasers (OSLs) using POFP. Gain narrowing with significant radiance increase was observed in the devices, giving evidence of the interference enhancement induced by microcavity and the lasing properties of POFP.

High-performance flexible inverted organic light-emitting diodes by exploiting MoS2 nanopillar arrays as electron-injecting and light-coupling layers

Inverted organic light-emitting diodes (IOLEDs) on plastic substrates have great potential application in flexible active-matrix displays. High energy consumption, instability and poor electron injection are key issues limiting the commercialization of flexible IOLEDs. Here, we have systematically investigated the electrooptical properties of molybdenum disulfide (MoS₂) and applied it in developing highly efficient and stable blue fluorescent IOLEDs. We have demonstrated that MoS₂-based IOLEDs can significantly improve electron-injecting capacity. For the MoS₂-based device on plastic substrates, we have achieved a very high external quantum efficiency of 7.3% at the luminance of 9141 cd m^-2, which is the highest among the flexible blue fluorescent IOLEDs reported. Also, an approximately 1.8-fold improvement in power efficiency was obtained compared to glass-based IOLEDs. We attributed the enhanced performance of flexible IOLEDs to MoS₂ nanopillar arrays due to their light extraction effect. The van der Waals force played an important role in the formation of MoS₂ nanopillar arrays by thermal evaporation. Notably, MoS₂-based flexible IOLEDs exhibit an intriguing efficiency roll-up, that is, the current efficiency increases slightly from 14.0 to 14.6 cd A^-1 with the luminance increasing from 100 to 5000 cd m^-2. In addition, we observed that the initial brightness of 500 cd m^-2 can be maintained at 97% after bending for 500 cycles, demonstrating the excellent mechanical stability of flexible IOLEDs. Furthermore, we have successfully fabricated a transparent, flexible IOLED with low efficiency roll-off at high current density.

Low efficiency roll-off and high performance OLEDs employing alkyl group modified iridium(iii) complexes as emitters

Four Ir(iii) dyes employing modified 1,2-diphenyl-1H-benzoimidazole ligands were synthesized. Doped device using tBu-Ir-PI with tert-butyl group as emitter achieves high η_c of 42.0 cd A⁻¹ and η_p of 27.0 lm W⁻¹, respectively.