Electron Multiplication for Thin Film Solar Gets Some Skeptics

Improving solar technology may need to find another line of research in place of "Multiexciton Generation"

2 min read
Electron Multiplication for Thin Film Solar Gets Some Skeptics

I have been very reluctant to get on the bandwagon that nanotechnology offered us any clear, never mind easy, solutions to getting solar power to be more efficient in generating electricity.

But I am always willing to consider the possibility that nanotechnology holds the key to making cheap and highly efficient solar power. One of the nano-related alternatives I discussed was the use of quantum dots for either electron multiplication or creating so-called “hot-carrier” cells.

As I had explained previously, “Electron multiplication involves making multiple electron-hole pairs for each incoming photon while with hot carrier cells the extra energy supplied by a photon that is usually lost as heat is exploited to make in higher-energy electrons which in turn leads to a higher voltage.”

The concept of electron multiplication has been a line of research vigorously pursued since 2004 when it was first proposed. In my blog on the subject, I highlighted research coming from the University of Minnesota and Texas that had investigated further the possibility of creating multiple charge carriers from one photon.

But Eran Rabani, a researcher at Tel Aviv University, was not so convinced by the research on electron multiplication.

"Our theory shows that current predictions to increase efficiencies won't work,” Rabani is quoted as saying in the linked article above. “The increase in efficiencies cannot be achieved yet through Multiexciton Generation, a process by which several charge carriers (electrons and holes) are generated from one photon."

Rabani has published two articles on his research, one is in the journal Chemical Physical Lettersand the other in Nano Letters

While Rabani seems to be dismissing this line of research and the possibility that more than one electron pair can be generated from one photon, he believes that by eliminating this line of research it will open up other research directions that are more promising for solar technology.

However, it’s not clear that this has permanently closed the door on Multiexciton Generation as Rabani quote seems to indicate: “The increase in efficiencies cannot be achieved YET through Multiexciton Generation.”

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3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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