Concentration of CO2 in the Atmosphere

The Quest for More Efficient Photovoltaics

George Harvey

Reports of a far more efficient solar cell has been developed is in the air.

Some of us may know of the “Shockley-Queisser” limit, regarding the efficiency limit of solar cells. It was named after the two scientists who first calculated the limits at the time. Its value, about 33.7%, means that theoretically, solar cells cannot convert more than 33.7% of the energy of the sunlight into electrical energy. The limit is “the maximum theoretical efficiency of a solar cell using a single p-n junction to collect power from the cell where the only loss mechanism is radiative recombination in the solar cell,” according to the Wikipedia article, “Shockley–Queisser limit.” ()

I am sure that is not perfectly clear to many of us, but we can still learn from it without knowing precisely what it means. First, the limit is theoretical, which means that there is a reason why it might be true, but it also might not be true. Next the limit only applies to a single “p-n junction.” From a practical perspective, that means the Shockley-Queisser limit does not apply to all solar cells. The same can be said for the question of the only loss mechanism being “radiative recombination in the solar cell.” The limit only applies to one, specific type of solar cell, and it is important because that type of solar cell is in widespread use.

An important implication is that the Shockley-Queisser limit will somehow govern the future of photovoltaics (PVs),. But it is probably not correct, because other types of solar cells might be developed, and they might have efficiencies greater than 33.7%.

Reports have been coming for some years about cells that actually do better. In 2022, the Fraunhofer Institute of Solar Energy Systems produced a solar cell that operated at a conversion rate of 47.6%, a pretty impressive improvement from 33.7%. How did they do this? They used an entirely different chemistry than the one the Shockley-Queisser limit applies to.

Now we find that things have been changed again. Researchers at Lehigh University reported in the journal Science Advances that they have achieved an “average photovoltaic absorption rate of 80% [efficiency]” in a prototype using a different chemistry and assembled in new ways.

The bottom line is that scientists believe that they may be able to produce far more efficient solar panels soon. And that means we will likely be able to produce far more electricity in the same amount of space.

We are still just starting our transition to renewable energy and addressing climate change. One thing we can bet on is that improvements will continue to move forward as our understanding of the science improves.

The technology can be compared with a Model T Ford. We have seen the prices of PVs decline sharply, in much the same way that the price of a Model T did, a hundred years ago. But the cars continued to improve for a long time after that car was developed. We can expect the same sort of improvement in renewable systems.

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