Hydrogen from sunlight: US researcher set conversion efficiency record

Built using inexpensive semiconductors, the device packs all components to make hydrogen and can be scaled.
Ameya Paleja
The photoreactor that achieved a 20.8% solar-to-hydrogen conversion efficiency.
The photoreactor that achieved a 20.8% solar-to-hydrogen conversion efficiency.

Gustavo Raskoksy/Rice University 

A research team led by Aditya Mohite, a professor of chemical and biomolecular engineering at Rice University in the US, has designed a device that can use sunlight to generate hydrogen, with a record efficiency of 20.8 percent, a press release said.

Hydrogen is being touted as the future of clean energy due to its high energy density that could be deployed even to fly large planes. However, the process of generating hydrogen is currently heavily dependent on fossil fuels. For hydrogen to herald a new future in clean energy, it needs to be produced sustainably and without carbon emissions.

Previous research has shown that energy from sunlight can be deployed to split water molecules and release hydrogen that can be isolated and then used as fuel. Such devices are referred to as photoelectrochemical cells because they carry out multiple functions, such as absorption of light, converting it to electricity, and then using it to split the water molecule all in one device.

Problems of photoelectrochemical cells

There have been multiple attempts made toward building the perfect photoelectrochemical cell with high energy conversion efficiency. Other research teams have also used perovskites, a material that has helped solar cells breach the 30 percent energy conversion ratio.

Unlike a solar cell, though, photoelectrochemical cells also have to deal with water which negatively impacts the perovskites. Coatings used to protect the perovskites end up hampering their function and decreasing the energy conversion efficiency of these green hydrogen generators.

Moreover, Mohite's team was looking for a low-cost solution so that they could use very expensive semiconductors either.

Two years to Eureka

The research team spent over two years trying out different combinations of materials and techniques to protect the halide perovskites they were using in their small reactor.

Hydrogen from sunlight: US researcher set conversion efficiency record
Still images from a video showing how the reactor works

After many lengthy trials, the researchers decided to use two different layers in their design. One would block the water from reaching the perovskite, while the other would make electrical contact between the protective layer and the perovskite.

The anti-corrosion barrier insulated the semiconductor from the ill effects of water, but the transfer of electrons was not impacted. The energy conversion efficiency achieved by the device was 20.8 percent, the most achieved without using solar concentration.

"It is a first for a field that has historically been dominated by prohibitively expensive semiconductors, and may represent a pathway to commercial feasibility for this type of device for the first time ever," said Austin Fehr, a biomolecular engineering doctoral student, who was involved in the study.

The researchers were also able to demonstrate that their barrier construct worked with different types of semiconductors and electrochemical reaction types, making it compatible with other systems and improving their workings too.

"We hope that such systems will serve as a platform for driving a wide range of electrons to fuel-forming reactions using abundant feedstocks with only sunlight as the energy input,” said Mohite in the press release.

"With further improvements to stability and scale, this technology could open up the hydrogen economy and change the way humans make things from fossil fuel to solar fuel,” added Fehr.

The research findings were published in the journal Nature Communications.


Achieving high solar-to-hydrogen (STH) efficiency concomitant with long-term durability using low-cost, scalable photo-absorbers is a long-standing challenge. Here we report the design and fabrication of a conductive adhesive barrier (CAB) that translates >99% of photoelectric power to chemical reactions. The CAB enables halide perovskite-based photoelectrochemical cells with two different architectures that exhibit record STH efficiencies. The first, a co-planar photocathode-photoanode architecture, achieved an STH efficiency of 13.4% and 16.3 h to t60, solely limited by the hygroscopic hole transport layer in the n-i-p device. The second was formed using a monolithic stacked silicon-perovskite tandem, with a peak STH efficiency of 20.8% and 102 h of continuous operation before t60 under AM 1.5G illumination. These advances will lead to efficient, durable, and low-cost solar-driven water-splitting technology with multifunctional barriers.

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