AI Article Synopsis

  • Ammonia solution etching on thermally-oxidised cuprous oxide (TO-CuO) significantly enhanced the photoelectrochemical (PEC) performance of photocathode devices used for water splitting, achieving record photocurrent densities.
  • The etching process removed interfacial traps that negatively impacted performance and resulted in diverse crystal morphologies, with high-index crystal orientations showing better PEC performance.
  • Analyses revealed the presence of metallic copper at the CuO/GaO interface, identified as a key limiting factor for PEC efficiency, stemming from the reduction of a CuO impurity layer during the device fabrication process.

Article Abstract

Ammonia solution etching was carried out on thermally-oxidised cuprous oxide (TO-CuO) in photocathode devices for water splitting. The etched devices showed increased photoelectrochemical (PEC) performance compared to the unetched ones as well as improved reproducibility. -8.6 mA cm and -7 mA cm photocurrent density were achieved at 0 V and 0.5 V versus the reversible hydrogen electrode (V), respectively, in the champion sample with an onset potential of 0.92 V and a fill factor of 44%. An applied bias photon-to-current efficiency of 3.6% at 0.56 V was obtained, which represents a new record for CuO-based photocathode systems. Capacitance-based profiling studies showed a strong pinning effect from interfacial traps in the as-grown device, and these traps were removed by ammonia solution etching. Moreover, the etching procedure gave rise to a diverse morphology of CuO crystals based on the different crystallographic orientations. The distribution of crystallographic orientations and the relationship between the crystal orientation and the morphology after etching were examined by electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM). The high-index crystal group showed a statistically higher PEC performance than the low-index group. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) revealed metallic copper at the CuO/GaO interface, which we attribute as the dominant trap that limits the PEC performance. It is concluded that the metallic copper originates from the reduction of the CuO impurity layer on the as-grown CuO sample during the ALD process, while the reduction from CuO to Cu is not favourable.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9116084PMC
http://dx.doi.org/10.1039/d1ee03696cDOI Listing

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