In 2018, Lawrence Berkeley National Laboratory demonstrated a single hybrid device that splits water with sunlight to produce hydrogen fuel and usable electricity simultaneously. Described in Nature Materials, the proof-of-concept married a photoelectrochemical water-splitting cell with an organic light-absorbing layer in a tandem stack. It reached 1.5 percent solar-to-hydrogen conversion efficiency while delivering about 0.4 milliwatts per square centimeter of electrical power.
The work was led by Gideon Segev, then a postdoctoral fellow, with senior author Ian Sharp. Its defining feature is a back-contact layout: the photovoltaic layer sits behind the photoanode, so the same sunlight drives both outputs instead of forcing a tradeoff. Conventional standalone water-splitters produce only hydrogen and discard the electrical byproduct. This one captures both.
How the Hybrid Device Works
A tandem cell that does two jobs
The unit combines a semiconductor-liquid junction with a rear organic photovoltaic film. In a standard water-splitting cell, the semiconductor absorbs photons and generates charge carriers that drive the reaction at the electrode surface. Berkeley Lab adds a second absorber behind the photoanode. That rear layer harvests the light that passes through and converts it into electricity. One device, one stream of sunlight, two usable outputs: hydrogen gas at the cathode and electrical power delivered to an external circuit.
Placement is everything. The photoanode grabs high-energy photons to oxidize water. Lower-energy photons slip through and feed the organic photovoltaic, so the two absorbers never compete for the same slice of the spectrum. That single-file arrangement lets the stack extract chemical and electrical energy from one beam of incident light.
Materials and Performance Metrics
Bismuth vanadate and organic photovoltaics
The photoanode is bismuth vanadate, a metal oxide semiconductor studied widely for solar water splitting. It absorbs visible light and holds up in aqueous electrolytes, a practical baseline for a submerged junction. The rear organic film uses a donor-acceptor pair; the specific chemistry was not disclosed in the paper.
The stack's 1.5 percent solar-to-hydrogen figure is low next to commercial photovoltaic electrolyzers that top 10 percent. But those systems are not single devices that co-generate. The modest electrical output proves the tandem routing works, delivering usable power without killing hydrogen production entirely.
Stability and Durability
Degradation under operation
Performance faded during testing. The study did not report exact test duration or a precise loss rate, but the authors flagged a decline over time. The weak link is the organic layer, which degrades when exposed to water and oxygen. The bismuth vanadate anode is tougher in aqueous conditions, yet the overall lifespan is capped by the rear absorber.
That fragility haunts every hybrid design in this field. The materials that enable the tandem routing are also the least durable component. The team did not claim to fix this. They showed the approach functions and measured its output, stopping well short of a stable commercial cell.
Context and Path Forward
Artificial photosynthesis and co-generation
Most artificial photosynthesis work aims to mimic a leaf: sunlight in, chemical fuel out. Usually that fuel is hydrogen or a carbon-based molecule, and nothing else. The Berkeley Lab device is an outlier because it co-generates hydrogen and electricity in one package. That dual output could suit a facility that needs both, though low efficiency and a short lifetime rule out near-term commercial use.
As of the 2018 Nature Materials publication, the device was not patented, licensed, or spun into a startup. Improvements in efficiency or stability after 2018 are not established here. What remains is a lab demonstration of a tandem stack that splits water and makes power at the same time, with durability and cost still unsolved.
Key Facts
- Research Institution: Lawrence Berkeley National Laboratory (Berkeley Lab), a U.S. Department of Energy national laboratory
- Publication: Nature Materials, 2018
- Principal Investigator: Gideon Segev (postdoctoral fellow) with senior author Ian Sharp
- Device Architecture: Tandem photoelectrochemical (PEC) cell with an organic photovoltaic (OPV) layer in a back-contact configuration
- Photoanode Material: Bismuth vanadate (BiVO4), a metal oxide semiconductor
- Solar-to-Hydrogen Efficiency: 1.5 percent
- Electrical Power Output: Approximately 0.4 milliwatts per square centimeter
