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Perovskite solar cells (PSCs) suffer from significant nonradiative recombination at perovskite/charge transport layer heterojunction, seriously limiting their power conversion efficiencies. Herein, solution-processed chromium multioxide (CrO x ) is judiciously selected to construct a MAPbI 3 /CrO x /Spiro-OMeTAD hole-selective heterojunction. It is demonstrated that the inserted CrO x not only effectively reduces defect sites via redox shuttle at perovskite contact, but also decreases valence band maximum (VBM)-HOMO offset between perovskite and Spiro-OMeTAD. This will diminish thermionic losses for collecting holes and thus promote charge transport across the heterojunction, suppressing both defect-assisted recombination and interface carrier recombination. As a result, a remarkable improvement of 21.21% efficiency with excellent device stability is achieved compared to 18.46% of the control device, which is among the highest efficiencies for polycrystalline MAPbI 3 based n-i-p planar PSCs reported to date. These findings of this work provide new insights into novel charge-selective heterojunctions for further enhancing efficiency and stability of PSCs.

Two-dimensional (2D) materials have attracted tremendous interests because of various advantages, such as high carrier mobility, favorable band gap, strong light-matter interaction, and flat dangling-bond-free surface. However, the photodetection performance of the pristine monolayer 2D materials is not competitive with that of their bulk counterpart due to the atomic thickness. Here, we demonstrated the direct growth of monolayer WS 2 on the Si 3 N 4 substrate by chemical vapor deposition. The porous morphology is formed at the surface of the Si 3 N 4 substrate during the growth process, and therefore, the as-grown WS 2 is partially suspended on porous Si 3 N 4 . The phototransistor based on as-grown monolayer WS 2 exhibits a high responsivity of 1.58 × 10 5 A/W and a fast response speed of 40 ms. Because of light resonant scattering of the porous Si 3 N 4 substrate, the absorption coefficient of monolayer WS 2 is enhanced from finite element analysis. In addition, biaxial tensile strain distribution in the partially suspended WS 2 induces a built-in in-plane electric field and less carrier mass from first-principles calculations. Therefore, we attributed the high performance of the phototransistor to the hybrid structure of partially suspended monolayer WS 2 on the porous substrate. Our present work paves a way to achieve high-performance monolayer photodetector from substrate morphology engineering.

Lithium−sulfur batteries are promising next-generation energy storage systems with high theoretical specific capacity. Despite extensive research efforts, it is still challenging to rationally design electrocatalysts with fast kinetics and effective adsorption of polysulfides. Herein, Fe-doped ReS 2 (Fe−ReS 2 ) ultrathin nanosheets are prepared as an electrocatalyst to trap the intermediates and accelerate the sulfur reduction reaction kinetics. Density functional theory calculations combined with activation energies in the multistep sulfur reduction reaction reveal that the Fe−ReS 2 considerably reduces the activation energy and optimizes the optimum adsorption strength of polysulfides and catalytic activity. The Fe−ReS 2 /S exhibits a highly reversible discharge capacity of 882.3 mA h g −1 at 1 C. For 500 cycles, the capacity fade rate is 0.013% per cycle. Moreover, in situ Raman spectroscopy measurements further confirmed that both sulfur reduction and oxidation processes were significantly enhanced by Fe−ReS 2 .