Article

Probing the Electronic Band Structure of Emerging Chalcogenide Absorbers for Photoelectrochemistry

Surface Analysis Spotlight: XPS 

by Kateryna Artyushkova     President

Band alignment is one of the biggest unknowns in photoelectrochemistry. You can have a material with the right bandgap, but if its band edges don’t line up with the reaction and transport layers, performance stalls and people end up “optimizing” the wrong bottleneck.

The paper “Probing the Electronic Band Structure of Emerging Chalcogenide Absorbers for Photoelectrochemistry” from researchers at Vrije Universiteit Brussel (https://pubs.acs.org/doi/10.1021/acs.jpcc.5c05834) tackles that problem by directly measuring the absolute positions of both band edges (valence and conduction) for several emerging chalcogenide absorbers and common transport layers. The key in their study is the combination of two surface-sensitive electron spectroscopies:

• UPS provides the valence-band edge (how hard it is to remove an electron)
• LEIPS provides the conduction-band edge (how easy it is to add an electron)

Most published studies measure one edge and infer the other from assumptions (electrochemical fits, models, or calculations). Measuring both edges on the same energy scale using the same instrument from exactly the same  area on the sample, answers the questions device designers care about:

• Is the conduction band high enough to drive a reduction reaction without wasting excess voltage?
• Is the valence band positioned to support oxidation?
• Which hole transport and electron transport layer choices create injection barriers that will dominate losses?

This work was done on a PHI VersaProbe platform configured with UPS + LEIPS, giving a straightforward experimental route to vacuum-referenced band-edge mapping in a single instrument ecosystem. The same configuration is available on the latest PHI XPS instrument – Genesis.

UPS+LEIPS combination turns “band alignment” from a debate into a measurement, and it helps reduce trial-and-error when designing photoelectrochemical stacks.  Findings reported by PHI customers establish a clear pathway to tailor absorber/transport layer combinations, accelerating the design of efficient, stable photoelectrochemical solar fuel systems.

The paper is in news!!! Belgian researchers are involved in a promising breakthrough to transform CO2... into sustainable fuels