Quantum Dot Solar Cells Break Conversion Efficiency Record

MIT researchers get 9-percent conversion efficiency out of quantum dot solar cells produced through solutions processes

2 min read
Quantum Dot Solar Cells Break Conversion Efficiency Record
Photo: Chia-Hao Chuang

Quantum dots have offered an attractive option for photovoltaics. Multijunction solar cells made from colloidal quantum dots (CQD) have been able to achieve around 7-percent conversion efficiency in the lab. While figures like this may not seem too impressive when compared to silicon solar cells, their promised theoretical conversion efficiency limit is an eye-popping 45 percent. This is possible because when a single photon is absorbed by a quantum dot, it produces more than one bound electron-hole pair, or exciton, thereby doubling normal conversion efficiency numbers seen in single-junction silicon cells.

Now researchers at the Massachusetts Institute of Technology (MIT) have raised the bar for quantum dot-based solar cells by producing one that changes light to electricity with 9-percent conversion efficiency. Furthermore, says the MIT team, it can be produced using an inexpensive production method that promises to keep manufacturing costs down.

The researchers, who published their findings in the journal Nature Materials, hit upon a way to produce quantum dot solar cells through a solution processing technique that doesn’t require high temperatures or a vacuum atmosphere to achieve stability for the solar cells when they are exposed to air. By using ligand treatments, which involve molecules or ions that bind to a central metal, the researchers were able to align the bands of the quantum dot layers, improving the performance of the films.

“Every part of the cell, except the electrodes for now, can be deposited at room temperature, in air, out of solution. It’s really unprecedented,” said graduate student Chia-Hao Chuang in a press release.

The processing technique for the quantum dot layers allows for the dots to do what they do well individually and also to work together in the transport of electrical charge to the edges of the film where it can then be collected to provide an electrical current.

Nine-percent efficiency may still seem low to casual observers, but the development of quantum dots for photovoltaics has been so rapid that researchers are impressed by the latest development.

“Silicon had six decades to get where it is today, and even silicon hasn’t reached the theoretical limit yet. You can’t hope to have an entirely new technology beat an incumbent in just four years of development,” said professor Vladimir Bulović in the release.

The researchers still need to determine why these films are so stable and there’s still a long way to go before they are commercially viable. But they now hold the National Renewable Energy Lab (NREL) record for quantum dot solar efficiency.

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How to Prevent Blackouts by Packetizing the Power Grid

The rules of the Internet can also balance electricity supply and demand

13 min read
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How to Prevent Blackouts by Packetizing the Power Grid
Dan Page
DarkBlue1

Bad things happen when demand outstrips supply. We learned that lesson too well at the start of the pandemic, when demand for toilet paper, disinfecting wipes, masks, and ventilators outstripped the available supply. Today, chip shortages continue to disrupt the consumer electronics, automobile, and other sectors. Clearly, balancing the supply and demand of goods is critical for a stable, normal, functional society.

That need for balance is true of electric power grids, too. We got a heartrending reminder of this fact in February 2021, when Texas experienced an unprecedented and deadly winter freeze. Spiking demand for electric heat collided with supply problems created by frozen natural-gas equipment and below-average wind-power production. The resulting imbalance left more than 2 million households without power for days, caused at least 210 deaths, and led to economic losses of up to US $130 billion.

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