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Defect Mitigation of Solution-Processed 2D WSe2 Nanoflakes for Solar-to-Hydrogen Conversion
journal contribution
posted on 2017-12-15, 18:33 authored by Xiaoyun Yu, Néstor Guijarro, Melissa Johnson, Kevin SivulaFew-atomic-layer nanoflakes of liquid-phase
exfoliated semiconducting
transition metal dichalcogenides (TMDs) hold promise for large-area,
high-performance, low-cost solar energy conversion, but their performance
is limited by recombination at defect sites. Herein, we examine the
role of defects on the performance of WSe2 thin film photocathodes
for solar H2 production by applying two separate treatments,
a pre-exfoliation annealing and a post-deposition surfactant attachment,
designed to target intraflake and edge defects, respectively. Analysis
by TEM, XRD, XPS, photoluminescence, and impedance spectroscopy are
used to characterize the effects of the treatments and photoelectrochemical
(PEC) measurements using an optimized Pt–Cu cocatalyst (found
to offer improved robustness compared to Pt) are used to quantify
the performance of photocathodes (ca. 11 nm thick) consisting of 100–1000
nm nanoflakes. Surfactant treatment results in an increased photocurrent
attributed to edge site passivation. The pre-annealing treatment alone,
while clearly altering the crystallinity of pre-exfoliated powders,
does not significantly affect the photocurrent. However, applying
both defect treatments affords a considerable improvement that represents
a new benchmark for the performance of solution-processed WSe2: solar photocurrents for H2 evolution up to 4.0
mA cm–2 and internal quantum efficiency over 60%
(740 nm illumination). These results also show that charge recombination
at flake edges dominates performance in bare TMD nanoflakes, but when
the edge defects are passivated, internal defects become important
and can be reduced by pre-annealing.
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Surfactant treatment resultsXPSliquid-phase exfoliated semiconducting transition metal dichalcogenidesedge site passivationH 2 evolutionXRDH 2 productionedge defectsSolar-to-Hydrogen Conversion Few-atomic-layer nanoflakesTMDsolution-processed WSe 2PECTEMSolution-Processed 2 D WSe 2 Nanoflakesphotocurrentpost-deposition surfactant attachmentnmperformance
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