A Novel Photocathode Material for Sunlight‐Driven Overall Water Splitting: Solid Solution of ZnSe and Cu(In,Ga)Se₂

Abstract

content; a similar effect has been found for other material systems. [21][22][23] As shown in Scheme 1, for a solid solution of ZnSe and CIGS, the VBM is expected to be deeper than that for CIGS, and the absorption edge longer than that for ZnSe. In this work, we investigated the PEC properties of (ZnSe) x (CIGS) 1-x thin-film photocathodes. The VBM was 0.25 V deeper than that for CIGS, and the onset potential was 0.89 V RHE , which is 0.17 V higher than that for CIGS. This higher onset potential allows PEC cells to be fabricated with a variety of photoanodes without the need for an external bias voltage. [24][25][26][27] Moreover, (ZnSe) 0.85 (CIGS) 0.15 contains much less of the rare metals indium and gallium. Therefore, (ZnSe) 0.85 (CIGS) 0.15 offers advantages over CIGS from the viewpoint of large-scale applications.Using a (ZnSe) 0.85 (CIGS) 0.15 photocathode with a BiVO 4 photoanode, [28] PEC overall water splitting without the need for an external bias voltage was demonstrated. The two-electrode cell produced stoichiometric amounts of H 2 and O 2 under simulated sunlight. The maximum STH was 0.91%, which is one of the highest values reported for a PEC cell containing a photoanode and a photocathode. [4] Results and Discussion PEC Properties of (ZnSe) 0.85 (CIGS) 0.15 PhotocathodesCurrent density versus potential curves for Pt and Pt/CdS modified (ZnSe) 0.85 (CIGS) 0.15 photocathodes are shown in Figure 1a. This composition was found to produce the largest photocurrent at 0.5 V RHE , as discussed in the next section.Whereas the photocathode modified by Pt alone showed a small cathodic photoresponse, the photocathode modified with both Pt and CdS exhibited a large photocurrent density of 6.5 mA cm −2 at 0 V RHE with a relatively high onset potential of 0.81 V RHE , which was defined as a cathodic photocurrent density of 0.05 mA cm −2 . It has been reported that an n-type CdS layer enhances the degree of charge separation by forming a p-n junction at the solid-liquid interface with the underlying p-type layer, which leads to a larger photocurrent and a higher onset potential because of the change in the band alignment. [29,30] As shown in Figure S1 (Supporting Information), the Pt/CdS/(ZnSe) 0.85 (CIGS) 0.15 photocathode showed no decay in the photocurrent at 0.1 V RHE over a period of more than 1 h. Such stable hydrogen evolution from water is similar to that reported for photocathodes based on chalcopyrites. [30][31][32] The incident photon to current conversion efficiency (IPCE) spectrum shown in Figure 1b indicates that the absorption edge is located around 900 nm. Despite the relatively high fraction of ZnSe, whose absorption edge is about 460 nm, the absorption edge for (ZnSe) 0.85 (CIGS) 0.15 is close to that for CIGS (≈1100 nm). Thus, due to its bandgap and onset potential, (ZnSe) 0.85 (CIGS) 0.15 is the promising material for sunlightdriven hydrogen production from water.Furthermore, insertion of 3-nm-thick Mo and Ti layers between the Pt and CdS improves the photocurrent around the onset potentia...

Promoting charge carrier utilization by integrating layered double hydroxide nanosheet arrays with porous BiVO4 photoanode for efficient photoelectrochemical water splitting

“…At an applied potential of about 0.75 V vs. RHE, the maximum ABPE of 1.07% can be achieved for BiVO4/NiFe-LDH photoanode. Moreover, the high efficiency achieved at a potential as low as 0.75 V vs. RHE provides a promising approach for assembling a tandem cell (water splitting [18,[43][44][45][46][47][48] or oxygen evolution coupling CO2 reduction to fuels [11,49,50]) or a PEC diode [1]. To further investigate the photoresponse of the BiVO4 and BiVO4/NiFe-LDH photoanodes, transient photocurrent measurements were carried out by LSV and chronoamperometry under chopped light illumination.…”

Enhanced Hydrogen Evolution under Simulated Sunlight from Neutral Electrolytes on (ZnSe)0.85(CuIn0.7Ga0.3Se2)0.15 Photocathodes Prepared by a Bilayer Method

“…As discussed in a previous report, the slight decrease in photocurrent is attributed to degradation of the CdS layer, as well as to mass transport effects. [7] Figure 4 a plots the variations in the IPCE with wavelength for each photocathode. Both devices exhibit sensitivity to light at wavelengths up to approximately 1000 nm.…”

Epitaxial growth of wafer-scale two-dimensional polytypic ZnS thin films on ZnO substrates

“…1 They have found practical applications in a wide variety of fields including solar cells, 2 integrated circuits, 3 solid-state lighting, 4 and sensors. 5 During the past decades, various routes, such as magnetic sputtering, 6 atomic layer deposition (ALD), 7 molecular beam epitaxy (MBE), 8 and metal organic chemical vapor deposition (MOCVD), 9 have been developed to synthesize semiconductor thin films. Among these strategies, of particular importance are the ones that are able to grow single-crystalline or polytypic thin films epitaxially.…”