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“Photochemical upconversion” could allow conventional solar cells to break 40% efficiency


April 22, 2012

University of Sydney researchers have developed a “photochemical upconversion” technique to increase the efficiency of solar cells (Photo: Noel McKeegan / Gizmag)

University of Sydney researchers have developed a “photochemical upconversion” technique to increase the efficiency of solar cells (Photo: Noel McKeegan / Gizmag)

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While the overall efficiency of conventional silicon solar cells has continued to improve in recent years, the technology faces a natural theoretical limit at around 33%. This is because the laws of physics prevent the cells from absorbing photons below a certain energy level, meaning that this low-energy light cannot be converted into electricity and is simply lost. Now researchers have found a way join two energy-poor red photons to form a single energy-rich yellow photon, allowing the harvesting of this part of the spectrum currently unused by single p-n junction crystalline silicon solar cells, and potentially enabling a record-breaking efficiency of 40%.

The technique, called “photochemical upconversion,” relies on two different types of molecules that are placed behind the solar cell in a solution to combine two low-energy photons into a single high-energy photon. The first type of molecule absorbs the energy-poor red photons, preventing them from escaping and storing them in a persistent state. This persistent state lasts long enough so that the energy can be transferred to a second, organic molecule when they encounter each other in the solution.

When two of these excited organic molecules then encounter each other, one returns to its base state and the other assumes a higher energy state. This higher-energy state is extremely short-lived, as the molecule then sends off a single yellow photon that is if a high enough energy to be absorbed by the solar cell.

Red light from a laser pointer is converted into higher-energy yellow light as it passes through the liquid photochemical upconverter (Photo: University of Sydney)

"We are able to boost efficiency by forcing two energy-poor red photons in the cell to join and make one energy-rich yellow photon that can capture light, which is then turned into electricity," says University of Sydney Associate Professor Schmidt who developed the so-called “turbo for solar cells” with partners at Helmholtz Centre Berlin for Materials and Energy. “We now have a benchmark for the performance of an upconverting solar cell. We need to improve this several times, but the pathway is now clear."

The photochemical upconversion technique was detailed in the journal Energy & Environmental Science, earlier this year.

Sources: University of Sydney, Helmholtz Centre Berlin for Materials and Energy

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag. All articles by Darren Quick

If only there was a cheep plentiful energy source that provided 24/7 electrical generation.


@slowburn so kind of avian power source that I'm not aware of ?

Inappropriate Response

cheep=cheap Spell check use to catch that. Even mild dyslexia is a serious pain.


Thus proving that heat really can flow from a cooler to a hotter body, after all. Right?


All energy is solar energy It will be so good for the long term prospects of the human race, when we are able to skip the prehisoric middle man.

Bradley Green

What is so wonderful, clean, clear, and inspiring about this article is that EFFICIENCY is discussed and honored and declared.

Not so about those 3 bladed fans that are extremely low efficiency and living symbols of the lemming instinct and insanely bum engineering. No they really aren't symbols of hope for humanity.

And the Betz limit of 59% efficiency was hit 32 years ago and ignored by every second idiot in the wind energy field. Flying ain't the answer.

Island Architect

Ralph: Not really. What this is doing is overcoming a limitation of bulk semiconductors using double absorption - something that happens in nature, just not frequently.

Heat can flow from a cooler to a hotter body, it just requires energy to make it happen reliably. If you look up "Maxwell's Demon" and "Peltier devices" you should get a pretty good look at an interesting way we do flow hear from cold to hot.

Charles Bosse

Dont worry soon we will break the 40% barrier lol been hearing that since the 80s remember that show beyond 2000? We are beyond 2000! Where is my mr fusion? I want to go back to future


This is a great approach to solve the problem of utilizing long wavelength light with out underutilizing the sort wave photons. To be practical a solid state version needs to be developed. One problem I see from the photograph is the absorption efficiency. The test sample of the fluid is much thicker than what could be economically used with photovoltaic cells.

This defiantly not an example of heat flow from cold to hot. The energy level of a single yellow photo is much less than the combined energy of two red photons. The "concentration" of the energy is allowed by thermodynamics because wast heat is also created.

Dominic From NASA

Great News for Solar Panels!

I hope this new idea can be applied in a very thin weather proof coating.


You can also double the power output of any solar panel by a reflector, which can be found on youtube.com



On Solar conversion to electricity.see www.suntco.com who has been working on Solar Liquid Power (SLP) for many years using electrochemistry and nanoscience to create the their SLP. They are pursuing investors now to ready for revenue and Mfg operations.


Hooray another advance in solar technology that is "5-10 years" away. I've been reading update after update with news about advances in solar panels but I can still only buy the crappy ones that have been around for decades. Where is my high efficiency, cheap, printed, flexible, durable, works in the shade, can be used as a window solar panel? It is all theory and no practice and has been for many years.


The biggest problem with all alternative power is that no one can fathom the idea of not using all energy through the grid. Grids have an important place but they blind us to the concept of getting things done in a manner other than right here right now. Make hay while the sunshines then burn the midnight oil. Use unreliable energy to run condensers filling water tanks for irrigation or whatever. When the energy is there you get water, when it isn't you don't but overall less energy is used to pump water from wherever. Or develop some other economically viable ways to use energy opportunistically. Trade speed for efficiency.

Snake Oil Baron

It is so unreasonable that I expect the lights to come on when I flip the switch and the water to flow when I turn the spigot.



The grid makes us dependent on gvt. I want independence in every sense. As soon as I can do so a reasonable cost I will free myself. I am not rich and I am frugal but I value my freedom so I would go for the new tech before it is competitive but it has to get closer.

One big advantage is the insurance against a solar flare that knocks out the grid for months or years. Another is fueling up my car at home from the sun.

Don Duncan
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