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Yasuyuki Hikita1 Takashi Tachikawa1 Motoki Osada2 Kyuho Lee3 Kazunori Nishio1 4 Hirohito Ogasawara5 Harold Hwang1 4

1, SLAC National Accelerator Lab, Stanford, California, United States
2, Stanford University, Stanford, California, United States
3, Stanford University, Stanford, California, United States
4, Stanford University, Stanford, California, United States
5, SLAC National Accelerator Laboratory, Menlo Park, California, United States

Metal oxide semiconductors are promising materials in photocatalytic and photoelectrochemical (PEC) water-splitting devices due to their high chemical stability, and flexibility in manipulating their physicochemical properties [1]. In addition to developing their bulk properties (optical absorption, electrical conductivity, etc.), tailoring the flatband potential at the oxide/electrolyte interface is essential for the enhancement of the spatial separation efficiency of photo-excited carriers [2]. We recently demonstrated the modulation of the flatband potential over 1.3 V by embedding a perovskite atomic dipole layer consisting of (LaO)+ and (AlO2)- just at the sub-surface of a (001)-oriented SrTiO3 (SrTiO3) photoanode [3]. While this large modulation showed the potential of this approach, the direction of the shift was opposite to that needed for improving the PEC performance for an n-type photoanode.

Here, we present a 400 mV flatband potential shift at the SrTiO3 (001)/electrolyte interface, successfully enhancing the photocurrent by ~10%. On a TiO2-terminated Nb-doped SrTiO3 (001) substrate, a negatively-charged oxide layer (AlO2)- and an ultrathin charge neutral SrTiO3 layers were sequentially grown by pulsed laser deposition. By immersing the entire structure in solution, the positively-charged ions adsorb onto the SrTiO3 surface to complete the dipole. This design strategy is based on our work on the solid-state analog, where we demonstrated a barrier height increase at oxide Schottky interfaces using a dipole created by a fixed oxide charge layer and induced electronic screening charge, instead of two oxide fixed charge layers [4]. The ability to independently manipulate the oxide/electrolyte interface energy levels greatly impacts the fundamental approach in developing heterostructures for photocatalytic and PEC applications. Details of the fabrication, PEC characterization, as well as spectroscopic results of these engineered photoelectrodes will be discussed in the presentation.

[1] A. Kudo, Y. Miseki, Chem. Soc. Rev. 38, 253 (2009).
[2] M. G. Walter et al., Chem. Rev. 110, 6446 (2010).
[3] Y. Hikita et al., Adv. Energy Mater. 6, 1502154 (2016).
[4] T. Yajima et al., Nature Commun. 6, 6759 (2015).

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