We
demonstrated an ultrahigh-performance and self-powered β-Ga2O3 thin film solar-blind photodetector fabricated
on a cost-effective Si substrate using a high-temperature seed layer
(HSL). The polycrystalline β-Ga2O3 thin
film deposited with HSL shows high performance in the solar-blind
region in comparison to the amorphous Ga2O3 thin
film deposited without HSL. The zero-bias digitizing sensor prototype
with an HSL produces a digitized output bit with deep UV (DUV) light
that exhibits a high on/off (I
254 nm/I
dark) ratio of >103, a record-low
dark current of 1.43 pA, and high stability and reproducibility over
100 cycles even after >2100 h. The photodetector shows minimum
persistent photoconductivity and fast response in milliseconds. The
photodetector yields a responsivity of 96.13 A W–1 with an external quantum efficiency of 4.76 × 104 at 5 V for 250 nm monochromatic light. The photodetector shows a
high response to even a rare weak signal of DUV (44 nW/cm2). These values are the highest reported to date for a planar β-Ga2O3 thin film based photodetector despite the use
of the cost-effective substrate. The asymmetric I–V curve indicates a dissimilar Schottky
barrier height at the two ends of the MSM photodetector, which is
discussed as the main reason for the high response even at zero bias.
This work provides the guidelines to develop a β-Ga2O3-based cost-effective, self-powered, high-performance,
and fast DUV photodetector that possesses a high potential for next-generation
practical solar-blind photodetector application.
We report effects of an interface between TiO2-perovskite and grain-grain boundaries of perovskite films prepared by single step and sequential deposited technique using different annealing times at optimum temperature. Nanoscale kelvin probe force microscopy (KPFM) measurement shows that charge transport in a perovskite solar cell critically depends upon the annealing conditions. The KPFM results of single step and sequential deposited films show that the increase in potential barrier suppresses the back-recombination between electrons in TiO2 and holes in perovskite. Spatial mapping of the surface potential within perovskite film exhibits higher positive potential at grain boundaries compared to the surface of the grains. The average grain boundary potential of 300-400 mV is obtained upon annealing for sequentially deposited films. X-ray diffraction (XRD) spectra indicate the formation of a PbI2 phase upon annealing which suppresses the recombination. Transient analysis exhibits that the optimum device has higher carrier lifetime and short carrier transport time among all devices. An optimum grain boundary potential and proper band alignment between the TiO2 electron transport layer (ETL) and the perovskite absorber layer help to increase the overall device performance.
Durable multifunctional electrocatalysts with zero emission and high catalytic activity are desirable for environmentally benign clean energy technologies such as water-splitting devices, fuel cells, and rechargeable metal−air batteries. Herein, we investigate a new antisite disordered polycrystalline double-perovskite oxide Ca 2 FeRuO 6 (CFR) material for catalytic activity. This makes it a remarkable electrocatalyst with excellent stability in a highly alkaline (1 M KOH) medium for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The bulk perovskite exhibits significant onset potentials of 0.9 V for ORR and 1.57 V vs the reversible hydrogen electrode (RHE) for OER, creating a superior bifunctional electrocatalyst. The novelty enhances for trifunctionality as it shows a moderate onset potential of −0.19 V vs RHE for HER. Substantially, the present material efficiently accelerates visible-light-driven water splitting for OER at neutral pH with excellent recyclability. The photo-/electroactive perovskite is an exceptional example of a heterogeneous catalyst for multifunctional activity. A plausible mechanistic pathway for the synergistic effects of e g orbit-filling in perovskite oxides for OER, ORR, and HER activities is proposed by density functional theory (DFT) calculations.
Commercial lithium-ion battery cells were cycled to various depths of discharge at various rates while the relative capacities were periodically measured. After 1000 cycles, lithium cobalt oxide (LiCoO 2) cathode material was extracted from the most severely aged cell. Nanoindentation was performed on individual LiCoO 2 particles. Fractures in these particles exhibited anisotropic behavior, which was confirmed by electron microscopy and diffraction examination indicating both intra-and inter-granular fracture occurred along {001} planes. Computation of the charge density structure for LiCoO 2 indicated that the Li-O bonds along the {001} planes require the lowest energy for cleavage, supporting the experimental findings. Atom probe tomography (APT) analysis indicated the nanoscale composition distributions within specimens from both fresh and cycled material. Among the cycled particles, nanoscale inhomogeneities in the Li content were observed. For APT specimens containing grain boundaries, accumulation of Li (up to 80 at%) on one side of the boundary was observed. Correlation of the electrochemical, mechanical, and compositional results indicates a combination of these mechanical and chemical mechanisms contributed to the measured capacity fade.
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