Cu(In,Ga)(S,Se)₂ Photocathodes with a Grown-In Cu_xS Catalyst for Solar Water Splitting

Abstract

As CuInGa-based chalcopyrite photocathodes suffer from poor hydrogen evolution activity, n-type overlayers and hydrogen evolution catalysts (HECs) need to be deposited on the film surface to drive surface band bending and reduce the overpotential for the hydrogen evolution reaction (HER). Here, we present a Cu­(In,Ga)­(S,Se)2 (CIGSSe) photocathode with grown-in Cu x S HECs enabling solar water splitting without the deposition of additional n-type overlayers and HECs. The controlled two-step chalcogenization using a Cu-rich CuInGa precursor film resulted in the natural formation of the Cu x S phase at the CIGSSe film surface and an increase in S content by substituting Se. Electrochemical water reduction tests elucidated that the naturally formed Cu x S alters the surface state of CIGSSe and reduces the overpotential for HER. Also, the S incorporation allows fine-tuning to make the CIGSSe band gap favorable for solar water splitting. Consequently, the CIGSSe photocathode showed −25.7 mA·cm–2 photocurrent density and 3 h photostability for photoelectrochemical hydrogen evolution.

Water Splitting: From Electrode to Green Energy System

“…Compared to Si solar cell, the outstanding advantage of CIGS is that the band gap energy can be modulated to effectively absorb the solar spectrum, so it is also widely used to achieve water splitting [129][130][131]. For purpose of overcoming the problem of low energy to drive overall water splitting, connected series into a monolithic device can be Fig.…”

Inverted Configuration of Cu(In,Ga)S2/In2S3 on 3D-ZnO/ZnSnO3 Bilayer System for Highly Efficient Photoelectrochemical Water Splitting

“…In this respect, significant progress has been achieved by multilayered photoelectrodes with the introduction of a different semiconductor having appropriate band alignment with metal oxides. Copper-based chalcopyrite semiconductor materials, more specifically CuInS 2 (CIS) and Cu­(In,Ga)­S 2 (CIGS) having a tunable bandgap in the range of 1.0–2.5 eV, have exhibited excellent light-harvesting ability as solar cell materials in the literature. , As a result of an excellent light-harvesting property in the visible region, which encompasses 43% of solar radiation in virtue of the narrower bandgap, the chalcopyrite semiconductor family including CuInS 2 , and Cu­(In,Ga)­S 2 − have proven to display superior performance as photoelectrodes in the PEC water splitting process as well.…”

Towards Highly Efficient Chalcopyrite Photocathodes for Water Splitting: The Use of Cocatalysts beyond Pt

“…[59] In addition, CuS can offer plenty of permeable channels for electrolyte diffusion due to its unique anisotropic structure. [60] Kim et al [61] reached a photocurrent density of approximately À 11.5 mA cm À 2 and a stable photocurrent of À 8 mA cm À 2 for 3 h at 0 V RHE , with a grown-in Cu x S method at Cu-rich CIGSSe (Cu x S/CIGSSe/Mo). Firstly, they deposited a Curich CuÀ In-Ga film with Cu/(In + Ga) = 1.00 ratio on Mo.…”

“…Due to the formation temperature of Cu x Se ( � 320 °C) being lower than that of Cu x S( � 360 °C), after the first step, the device resulted in a Se-rich state compared to the S content. [61] However, after the second step, it resulted in an S-rich state and the natural formation of the Cu x S film since the remained Cu reacted with S at the second step. Finally, since it reached a photocurrent density comparable to devices that uses Pt, the copper sulfide was shown to be a suitable environment-friendly and cocatalyst candidate.…”