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Layered transition metal dichalcogenide (TMD) crystals in reduced dimensions have exhibited a wide range of extraordinary physical and chemical properties spanning from exotic quantum phenomena to unusually superior chemical reactivity. Their anisotropic van der Waals (vdW) bonding nature enables them to commonly possess two-dimensional (2D) structures which have been rigorously investigated recently. Nonetheless, TMD crystals in quasi zero-dimensional (0D) forms, i.e., TMD fullerenes, have not been explored in depth from the perspective of reproducible synthesis and process–structure correlation. Herein, we report a controlled synthesis of inorganic fullerene platinum diselenide (PtSe2) via a thermal selenization of Pt nanostructured precursors. We identified a conversion of Pt nanocubes to PtSe2 "onion-like" fullerenes, dictated by a well-defined isotropic volume expansion. Extensive transmission electron microscopy (TEM) inspections revealed that there exists a certain size-dependency which leads to the preferable growth of PtSe2 fullerenes over 2D PtSe2 platelets. The underlying principle for this size-dependent growth is discussed in the context of surface energy minimization. Furthermore, the PtSe2 fullerenes were verified to possess a large degree of unsaturated dangling bonds as well as internal strain, verified by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) as well as a geometric phase analysis (GPA). This study sheds light on synthesizing a wide range of TMD-based fullerenes which will foster the discovery of novel physical and chemical properties in quasi 0D material systems. [ABSTRACT FROM AUTHOR]

This study examines the influence of the growth mode on defect formation and strain relaxation in GaN thin films grown on cone-shaped patterned sapphire (CSPS) substrates by metal-organic chemical vapor deposition. A dramatic reduction in the luminescence dark spot density and a red-shifted excitonic emission were found for GaN on CSPS compared to GaN on planar sapphire substrates. The results also show that both the crystal quality and optical properties are improved in GaN on CSPS with a strong spatial correlation between the dark spots and local structural properties due to the induced-lateral overgrowth on the cone-shaped patterns. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate that two-dimensional (2D) CdSeS quantum dot monolayers (QDM) can strongly influence efficient charge transport and charge separation, improving the performance of inverted polymer solar cells (iPSCs). Also, for the first time we report the electronic band structure of CdSeS and CdSeS@ZnS QDs and an effective approach to apply the 2D QDM as an effective electron transport layer in iPSCs from work function studies. The iPSCs with the 2D CdSeS QDM showed maximum power conversion efficiencies of 8.83%, which were 26% higher than the reference. Ultraviolet photoelectron spectroscopy and time-correlated single photon counting (TCSPC) measurements were performed to confirm the charge separation and electron transport behavior in the iPSCs with 2D QDMs. The PL decay time of the iPSCs with the CdSeS QDM at 720 nm was ∼60 ps, which is much faster than that of the iPSCs without the 2D QDM. The enhanced photovoltaic performance of the iPSCs with the 2D CdSeS QDM can be attributed to the effective charge separation and electron transport performance due to the high built-in voltage and fast exciton decay time from the 2D QDM. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2) has been extensively used as a hole transport layer in many inverted polymer solar cell devices. However, its potential as an electron transport layer in a solar cell device has rarely been reported. In this paper, we demonstrate an iPSC with enhanced photovoltaic performance by the introduction of a MoS2 nanosheet (NS) interlayer. Herein, MoS2 NS thin films were uniformly deposited on a polyethylenimine ethoxylated polymer by an electrostatic interaction. The MoS2 NS interlayer in the iPSC device plays important roles as a sub-photo sensitizer and an electron transport layer and provides effective charge separation for the enhancement of device performance. iPSCs with MoS2 NSs based on bulk heterojunction active materials such as P3HT:PC60BM, PTB7:PC71BM and PTB7-Th:PC71BM showed maximum power conversion efficiencies of 3.54%, 8.12%, and 9.08%, respectively, which were 27%, 11%, and 15% higher than those of the reference, respectively. Furthermore, the enhanced photovoltaic performance and electron transport mechanism of the iPSCs with the MoS2 NSs were confirmed experimentally using finite-difference-time-domain modeling and time-correlated single photon counting (TCSPC) measurements. The computational simulation results showed that the light absorption of the iPSCs with the MoS2 NS interlayer was slightly better than that of the iPSCs without the MoS2 NS interlayer. The electron decay time of PTB7:PC71BM with the MoS2 NS interlayer at a wavelength of 700 nm was reduced to 60 ps from 100 ps of PTB7:PC71BM without the MoS2 NS interlayer. The efficient light absorption and electron transfer characteristics of MoS2 NSs significantly improved the photovoltaic conversion performance of the iPSC devices. [ABSTRACT FROM AUTHOR]