Optical and electrical features of semitransparent CuO photoelectrochemical cell

The data presented in this article are related to the research article entitled “CuO photocathode-embedded semitransparent photoelectrochemical cell” (Patel et al., 2016) [1]. This article describes the growth of Cu oxides films using reactive sputtering and application of CuO photocathode in semitransparent photoelectrochemical cell (PEC). In this data article, physical, optical and electrical properties, and PEC performances data set of the reactively sputtered semitransparent CuO samples are made publicly available to enable extended analyses.


a b s t r a c t
The data presented in this article are related to the research article entitled "CuO photocathode-embedded semitransparent photoelectrochemical cell"   [1]. This article describes the growth of Cu oxides films using reactive sputtering and application of CuO photocathode in semitransparent photoelectrochemical cell (PEC). In this data article, physical, optical and electrical properties, and PEC performances data set of the reactively sputtered semitransparent CuO samples are made publicly available to enable extended analyses.
& 2018 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Subject area
Materials Engineering, Physics, Electrochemistry More specific subject area

Solar Energy
Type of data Figures, Table  How  Approaches to modulate the morphologies of CuO x films. A simple and powerful reactive sputtering method can be applied to tune the CuO x films. The surface morphology of various Cu oxides was obtained by changing the oxygen flow rate during the sputtering process.
RTP effect is significant and effective to enhance the crystallinity of CuO x films. The Mott-Schottky analysis confirms the modulation of built-in potential of CuO x films.
Tuning of the optical band gap of semitransparent CuO photocathode would be useful for bandgap engineering and applied for advanced CuO embedded photoelectrochemical cells.

Data
The comparison for the reactive-sputtered semitransparent CuO photocathode was presented in Table 1. This summary is presented in the chronological order. The readers can easily overview the progress of Cu oxide-based PEC cells. Fig. 1 shows the photographs of the reactive sputtered CuO x films and images after RTP. The surface morphologies of the various Cu oxides grew by various oxygen flows and RTP treatments are presented in Fig. 2. The film thickness measured using the surface profiler is presented in Fig. 3. Reflectance characteristics and Tauc plots of CuO samples are presented in Figs. 4 and 5, respectively. Frequency dependent Mott-Schottky measurement of RTP-treated CuO samples is presented in Fig. 6. Fig. 7 shows the free carrier concentrations and flat band potential of CuO samples according to the Mott-Schottky analysis. Table 1 Performance comparison for our nanoscaled CuO photocathode with the CuO based photocathodes in literature. Reference potential for measured photocurrent density is mentioned as reversible hydrogen electrode (RHE), silver/silver chloride (Ag/AgCl) and saturated calomel electrode (SCE). Photocurrent value given in this work is the average value of total 3 electrodes.

Preparation of CuO x films
Large scale (Ø4 in.) Cu target (purity 99.99%) was reactively sputtered to form various phases of copper oxides (CuO x ) at room temperature. The reactive gas (O 2 ) and the sputtering gas (Ar) were simultaneously supplied to tune the phases CuO x by changing the O 2 flow rate (1-9 sccm) at a fixed Ar supply (30 sccm). Three types of CuO x phases were achieved for Batch-1 (Ar/O 2 of 30/1 sccm), Batch-3 (Ar/O 2 of 30/5 sccm), and Batch-5 (Ar/O 2 of 30/9 sccm). To control the of CuO x film properties, rapid thermal process was performed for 10 min at 550°C. The RTP-treated samples were denoted as Batch-2 (RTP-treated Batch-1), Batch-4 (RTP-treated Batch-3), and Batch-6 (RTP-treated Batch-5), respectively [1]. In order to remain a pure FTO, the Krypton tape was partially covered the FTO glass and removed after the reactive sputtering process.

PEC Mott-Schottky measurements
The potentiostat/galvanostat (PG-stat; ZIVE SP1, WonA Tech, Seoul, South Korea) was applied for the PEC Mott-Schottky measurements in a three electrodes cell. Copper oxide-coated FTO, Ag/ AgCl, and platinum gauze were connected to the working, reference, and counter electrodes of the PG-stat, respectively. Aqueous 0.1M NaOH solution was used as an electrolyte for all PEC measurements.
The measured potential V vs. Ag/AgCl was converted to the reversible hydrogen electrode (RHE) scale according to the Nernst equation:    700 1200