$Mg_xZn_{1-x}O$ contact to $CuGa_3Se_5$ absorber for photovoltaic and photoelectrochemical devices

TL;DR

This study explores the use of Mg_xZn_{1-x}O as a contact layer for CuGa_3Se_5 in photovoltaic and photoelectrochemical devices, demonstrating promising open circuit voltages after surface treatment.

Contribution

It introduces Mg_xZn_{1-x}O as a novel contact material for CuGa_3Se_5, addressing surface oxidation issues and optimizing electronic properties for tandem PEC water splitting.

Findings

Achieved an onset potential close to 1 V vs RHE.

Surface treatment with Cd^{2+} alters surface chemistry and electronic structure.

Open circuit voltage near 1 V indicates potential for tandem PEC applications.

Abstract

$CuGa_3Se_5$ is a promising candidate material with wide band gap for top cells in tandem photovoltaic (PV) and photoelectrochemical (PEC) devices. However, traditional CdS contact layers used with other chalcopyrite absorbers are not suitable for $CuGa_3Se_5$ due to the higher position of its conduction band minimum. $Mg_xZn_{1-x}O$ is a transparent oxide with adjustable band gap and conduction band position as a function of magnesium composition, but its direct application is hindered by $CuGa_3Se_5$ surface oxidation. Here, $Mg_xZn_{1-x}O$ is investigated as a contact (n-type buffer or window) material to $CuGa_3Se_5$ absorbers pretreated in $Cd^{2+}$ solution, and an onset potential close to 1 V vs RHE in 10 mM hexaammineruthenium (III) chloride electrolyte is demonstrated. The $Cd^{2+}$ surface treatment changes the chemical composition and electronic structure of the $CuGa_3Se_5$ surface, as demonstrated by photoelectron spectroscopy measurements. The performance of $CuGa_3Se_5$ absorber with $Cd^{2+}$ treated surface in the solid-state test structure depends on the Zn/Mg ratio in the $Mg_xZn_{1-x}O$ layer. The measured open circuit voltage close to 1 V is promising for tandem PEC water splitting with $CuGa_3Se_5$/$Mg_xZn_{1-x}O$ top cells.