Enhancement of the photoelectrochemical properties of a CuGaSe2-based photocathode for water reduction induced by loading of a Cu-deficient layer at the p–n heterointerface

Abstract

Photoelectrochemical activity for water reduction (H2 liberation) over a co-evaporated CuGaSe2 compact thin film modified with a CdS layer and Pt deposits under simulated sunlight (AM 1.5G) radiation was evaluated, specifically focusing on the impact of a Cu-deficient layer (CDL) loaded on the top part of the CuGaSe2 film. It was found that the intentional loading of the CDL with an appropriate thickness was effective for achieving a large current flow and relatively positive photocurrent onset. The half-cell solar-to-hydrogen efficiency reached 6.6% over the best photocathode used. Moreover, the highest photocurrent onset potential of more than 0.9 V vs reversible hydrogen electrode was achieved over the photocathode based on the CuGaSe2 film having an extremely thick CDL (200 nm) with a relatively thick CdS layer (90 nm) due to efficient spatial separation of photogenerated carriers.

Enhanced Performance of Ternary CuGaSe2 Thin‐Film Photovoltaic Solar Cells and Photoelectrochemical Water Splitting Hydrogen Evolution with Modified p–n Heterointerfaces

“…CDL, as can be observed by comparing types A and B. This result is consistent with our previous finding, [26] and an HC-STH efficiency of over 7% (0.65 V vs RHE) was obtained in this study. This HC-STH efficiency is the highest among the values reported for ternary CGSe-based photocathodes to date.…”

“…CDL were slight, [ 38 ] whereas considerable improvements in the EQE and current density were observed for the PEC cells. [ 26 ] The type D PEC cell demonstrated improved performance compared to the type A cell, but the performance was not better than those of the type B and C cells. The PEC performance of the type D cell may depend on the Rb concentration in the addnl.…”

“…[25] We also previously found that CGSe PEC cells exhibited Faradaic efficiencies of almost unity (99%) and confirmed stable hydrogen evolution at an applied potential of 0 V versus RHE. [26] Nonetheless, degradation was observed when the reaction occurred at an applied potential of 0.5 V versus RHE, possibly due to photocorrosion of CdS in the solution. [50,51] These results suggest that improving the durability and PEC performance by employing more stable and suitable n-buffer materials than CdS in terms of the chemical properties and energy band diagram is important.…”

“…[ 23 ] Recently, we demonstrated an HC‐STH efficiency of 6.6% using a CGSe photocathode prepared using a Cu‐deficient surface CGSe film. [ 26 ] This value is quite high among the ternary CGSe‐based photocathodes reported to date and represents a considerable advancement. Nevertheless, PEC water splitting hydrogen evolution merits long‐term study to achieve highly efficient, cost‐effective, and durable solar energy conversion devices; thus, further progress is required for practical applications.…”

Molecular Coatings Improve the Selectivity and Durability of CO2 Reduction Chalcogenide Photocathodes

“…Additionally, the 1.2–1.3 eV band gap of the most common CIGS absorber, CuIn 0.7 Ga 0.3 Se 2 , is lower than ideal for most photoelectrochemical architectures. More recently, the wider band gap CuGaSe 2 , − Cu­(In,Ga)­(S,Se) 2 , , and (Ag,Cu)­GaSe 2 , chalcopyrite photocathodes have shown promise for PEC water splitting. Recent work has also expanded the use of CIGS-based photocathodes to CO 2 reduction (CO 2 R). − …”