Sulfur Selenium Balance Boosts Solar Hydrogen Yield

Estimated reading time: 5 minutes · Last updated: 11 October 2026

Researchers at the Daegu Gyeongbuk Institute of Science and Technology (DGIST), with collaborators at Konkuk University, demonstrate that tuning the sulfur‑to‑selenium ratio in CuIn(S1−xSex)2 quantum dots eliminates key anion vacancies and lifts photoelectrochemical performance. Published on 1 September 2026 in eScience (DOI: 10.1016/j.esci.2025.100518), the paper shows an equimolar CuIn(S0.5Se0.5)2 composition yields the fewest sulfur and selenium vacancies, particle sizes of about 4.3 nanometres, and, when incorporated into TiO2 photoanodes with ZnS/SiO2 passivation, a record 15.1 mA cm⁻² photocurrent at 0.6 V versus RHE and Faradaic efficiency above 80% for more than six hours.

How a composition-driven strategy controls defects

Multinary I–III–VI semiconductor quantum dots are prone to native anion vacancies that trap carriers and reduce photoelectrochemical yield. The team at Daegu Gyeongbuk Institute of Science and Technology varying the sulfur‑to‑selenium ratio across five CuIn(S1−xSex)2 compositions while holding particle size and cation stoichiometry steady, isolating the anion chemistry as the variable that controls vacancy formation.

Using extended X‑ray absorption fine structure spectroscopy, the researchers recorded higher coordination numbers for copper and indium in the equimolar composition; electron paramagnetic resonance measurements confirmed this composition had the lowest concentration of sulfur and selenium vacancies. Their interpretation is mechanical: balancing the anions reduces local lattice strain and the tendency for vacant sites to form, which in turn limits recombination pathways that steal photogenerated carriers.

This work frames the problem in practical terms: rather than relying on external dopants or toxic heavy metals, defect densities can be tuned through stoichiometry control. The paper presents this as a general design principle for defect engineering in multinary quantum dots and calls it a composition-driven defect control approach.

Why the equimolar CuIn(S0.5Se0.5)2 composition performs better

The equimolar CuIn(S0.5Se0.5)2 sample combined structural and electronic advantages. X‑ray diffraction showed the smallest tetragonal lattice distortion for that composition, which the authors link to lower crystal strain. Lower strain reduces the energetic drive for anion vacancies to form, and EXAFS data showed higher coordination for both copper and indium relative to other mixes.

Time‑resolved photoluminescence and carrier measurements indicated substantially extended carrier lifetimes and a hole concentration nearly double that of the pure sulfide composition. Those two changes — fewer recombination sites and more mobile holes — are the proximate cause of higher photocurrent in photoelectrochemical operation.

In short, balancing sulfur and selenium at the atomic scale reduced intrinsic defects and improved the optoelectronic properties that matter most for converting sunlight into charge carriers that drive hydrogen evolution.

Device integration: passivation, architecture and record photocurrent

To validate the optimized quantum dots, the DGIST–Konkuk University team coupled them to titanium dioxide (TiO2) photoanodes and applied a dual ZnS/SiO2 passivation stack. Those passivation layers both limit interfacial recombination and protect the quantum dots from photocorrosion during water‑splitting.

In that configuration the team reports a photocurrent density of 15.1 mA cm⁻² measured at 0.6 V versus the reversible hydrogen electrode (RHE). The authors describe this as a record for heavy‑metal‑free quantum‑dot photoanodes, and they attribute the outcome to the combination of lower vacancy density, longer carrier lifetimes and the protective dual passivation.

Durability trials ran continuously for more than six hours and retained Faradaic efficiency above 80%, demonstrating the passivation strategy’s importance for short‑term operational stability. The paper presents these device tests as a proof of concept that defect‑engineered, toxic‑metal‑free quantum dots can reach practical performance levels.

Implications for scale-up and wider optoelectronic use

By avoiding cadmium and lead, the approach removes a major environmental and regulatory barrier to scaling quantum‑dot photocatalysts. The team suggests the composition‑control technique could be transferred to quantum‑dot solar cells, photodetectors and light‑emitting devices, where careful defect management is also important.

However, translating a laboratory composition control to manufacturing requires reproducible synthesis that holds particle size, cation stoichiometry and the precise sulfur/selenium balance across large batches. The paper is positioned as a materials‑science foundation: it establishes a design rule rather than a turnkey manufacturing recipe.

Funding came from the National Research Foundation of Korea (NRF; grant RS‑2024‑00444458), the Ministry of Trade, Industry and Energy (MOTIE) and the Korea Institute for Advancement of Technology (KIAT; grant P0026257), among other programmes. The full results are published in eScience, Volume 6, Issue 5, Article 100518 (impact factor 52.9).

Case for and against near-term impact

The bottom line

The DGIST–Konkuk University team presents a materials strategy of tuning the sulfur/selenium balance in CuIn(S1−xSex)2 quantum dots to suppress anion vacancies, thereby restoring carrier lifetimes and hole populations needed for efficient solar hydrogen generation. Their device measurements — 15.1 mA cm⁻² at 0.6 V versus the RHE and a sustained Faradaic efficiency above 80% for more than six hours — indicate that heavy‑metal‑free quantum dots could be a lower‑toxicity option for photoelectrochemical hydrogen production. The next steps are to demonstrate reproducible, large‑scale synthesis and to verify long‑duration operational stability before industrial assessment.

What to watch

• Watch for independent replication of the CuIn(S0.5Se0.5)2 vacancy and photocurrent results; no date has been set.
• Watch for follow‑up publications reporting stability beyond six hours or outdoor testing; no date has been set.
• Watch for announcements of pilot demonstrations or industrial partnerships to scale the ZnS/SiO2‑passivated photoanode; no date has been set.