Search

Quasi-2D metal halide perovskites are promising candidates for light-emitting applications owing to their large exciton binding energy and strong quantum confinement effect. Usually, quasi-2D perovskites are composed of multiple phases with various numbers of layers (

Quasi-2D CsPbBr3 perovskites hold great potential as the promising emitters for perovskite light-emitting diodes (PeLEDs) owing to their good film morphology, excellent thermal stability and efficient radiative recombination. However, quasi-2D CsPbBr3 films are usually composed of multiple phases with various numbers (n) of [PbBr6]4− octahedral layers, and the formed n = 1 phase shows nonradiative recombination and retarded exciton transfer, which are detrimental to the performance of PeLEDs. Here, we report a facile approach to grow quasi-2D CsPbBr3/Cs4PbBr6 nanocomposite films as the emissive layers (EMLs) for efficient PeLEDs by simply introducing excess CsBr in the precursor solution. In the perovskite nanocomposite films, it is found that the formation of the n = 1 phase is completely suppressed and the density of trap states is dramatically lowered, leading to the significant reduction of nonradiative losses. In addition, the formed Cs4PbBr6 with a large bandgap can centralize carriers and confine excitons in quantum wells to realize efficient transfer, and can also constrain the crystal size and enhance the exciton binding energy of CsPbBr3, all of which facilitate the radiative recombination. As a result of the reduced nonradiative losses and improved radiative recombination, the green PeLED based on the quasi-2D CsPbBr3/Cs4PbBr6 nanocomposite EML achieves greatly enhanced performance with a maximum external quantum efficiency (EQE) of 11.84%, which is much higher than the maximum EQE of 1.94% of the quasi-2D CsPbBr3 device. This study demonstrates that the construction of perovskite nanocomposites should provide an effective way to promote the performance of PeLEDs.

1,4-butanediamine (BEA) is incorporated into FASnI3 (FA=formamidinium) to develop a series of lead-free low-dimensional Dion-Jacobson-phase perovskites, (BEA)FAn-1 Snn I3n+1 . The broadness of the (BEA)FA2 Sn3 I10 band gap appears to be influenced by the structural distortion owing to high symmetry. The introduction of BEA ligand stabilizes the low-dimensional perovskite structure (formation energy ca. 106 j mol-1 ), which inhibits the oxidation of Sn2+ . The compact (BEA)FA2 Sn3 I10 dominated film enables a weakened carrier localization mechanism with a charge transfer time of only 0.36 ps among the quantum wells, resulting in a carrier diffusion length over 450 nm for electrons and 340 nm for holes, respectively. Solar cell fabrication with (BEA)FA2 Sn3 I10 delivers a power conversion efficiency (PCE) of 6.43 % with negligible hysteresis. The devices can retain over 90 % of their initial PCE after 1000 h without encapsulation under N2 environment.

Hydrogen evolution reaction (HER) is a vital step for electrochemical energy conversion technologies. However, developing cost-efficient electrocatalysts remains a huge challenge. Here, we report that Cr-doped NiSx (Cr-NiSx) in situ grown on Ni foam via a hydrothermal sulfurization reaction can be an ultra-highly efficient and low-cost electrocatalyst for HER in alkaline condition. We find that the Cr-doping can trigger the formation of NiS and NiS1.19, leading to the suppression of Ni3S2 in the nanostructure. We show that Cr-NiSx exhibits an excellent HER activity with an ultralow overpotential of 81 mV at 10 mA cm−2, better than those of most nickel sulfide catalysts, and good stability. Our combined experimental and computational study reveals that the excellent performance is contributed by: (1) stabilized NiSx phase, (2) strongly improved conductivity, (3) greatly enhanced active sites, and (4) reduced Gibbs free energy for hydrogen adsorption (ΔGH) due to the Cr-doping. We believe that this work provides a simple approach to design cost-effective and ultra-highly efficient HER electrocatalysts for practical applications.