Chalcogenide semiconductors push solar fuel systems toward low cost CO2 conversion

by Robert Schreiber
Brussels, Belgium (SPX) Dec 09, 2025

Researchers at the Vrije Universiteit Brussel and partners have mapped how emerging chalcogenide semiconductor absorbers behave in photoelectrochemical systems that convert sunlight and CO2 into chemical fuels. They examined how the electronic band structure of these materials governs charge generation, separation, and transfer at the semiconductor - electrolyte interface, and how these processes limit device efficiency over time.

The team focused on using non-toxic, earth-abundant compounds as light absorbers, aiming to replace critical or scarce elements in solar fuel architectures. By probing the band positions and internal electric fields, they identified how the absorber layers couple electronically to underlying contacts and to the catalyst - electrolyte side, clarifying which configurations favor efficient charge extraction.

Through detailed measurements, the researchers linked changes in photoresponse to specific degradation pathways in the absorbers and interfaces. This allowed them to pinpoint how defects, surface states, and interface reactions affect long-term stability, and which material treatments improve durability under operating conditions.

The study also shows that adding tailored electrocatalysts at the reactive interfaces strengthens overall device performance. These catalysts facilitate the desired redox reactions and help maintain the activity of the semiconductor over many operating cycles, extending operational lifetimes without relying on scarce elements.

According to first author Beatriz de la Fuente, the work demonstrates that solar fuel systems can be built from materials that are both widely available and compatible with environmental and safety constraints. "Our findings show that it is possible to build solar fuel systems with abundant, environmentally friendly materials that are both efficient and sustainable," says Beatriz de la Fuente. "This is a crucial step in turning CO2 from a problem into a valuable resource."

The results support the development of integrated photoelectrochemical devices that use CO2 as a feedstock for fuel production rather than as a waste stream. In the near term, the insights into band structure, interfaces, and catalyst coupling provide guidelines for designing scalable systems, while in the longer term, such devices could be deployed as decentralized units that produce solar fuels and contribute to climate and energy goals.

The work was carried out within the SUME (Sustainable Materials Engineering) group at VUB in collaboration with Stanford University, Antwerp University, and Hasselt University. It is part of SYNCAT (SYNergetic Design of CATalytic Materials for Integrated Photo and Electrochemical CO2 Conversion Processes), a multi-university project funded through the Flemish Moonshot Initiative (Strategic Basic Research for Clusters) by VLAIO, with additional support from the Research Foundation Flanders (FWO).

Research Report:Probing the Electronic Band Structure of Emerging Chalcogenide Absorbers for Photoelectrochemistry