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A new method for making cheaper and more efficient solar cells

The sun will provide more than enough energy to fulfill all our needs, only if we can use it cheaply and efficiently. Solar energy could provide a clean alternative to fossil fuels, but the high cost of producing solar cells is a significant limitation to their widespread use.

Stacey Bent, professor of chemical engineering, holds a quantum dot-based solar cell
Stacey Bent, professor of chemical engineering, holds a quantum dot-based solar cell

Researchers from Stanford University in the US have found that adding a single layer of organic molecules to the solar cell can increase its efficiency threefold, and can also lead to the development of cheaper and more efficient solar panels. The findings of this study were published in the scientific journal DHW Nano.

Chemical engineering professor Stacey Bennett became interested in developing a new type of solar technology two years ago. These solar cells use tiny semiconductor particles called "quantum dots." The production of quantum dot-based solar cells is cheaper than conventional methods, since it uses simple chemical reactions. However, despite the promise inherent in them, they lag far behind existing solar cells in terms of efficiency.

"I wonder if we can use our knowledge of chemistry to improve their efficiency," says the researcher. If it does succeed in doing so, the lower cost of these solar cells could lead to widespread adoption of this technology. In principle, cells based on quantum dots will be able to achieve higher efficiency, the researcher explains, and this is due to basic limitations of normal solar cells.

Solar cells work by using energy from the sun to energetically excite electrons. These excited electrons move from a lower energy level to a higher level, leaving a "hole" where they came from. Solar cells use a semi-conducting material to conduct the electrons in one direction, and a different material to conduct the holes in another direction. This flow of electrons and holes is responsible for receiving an electric current.

However, a certain minimum amount is required to completely separate the electron from its hole. This amount is different for each material and depends on the wavelength (color) of the light that the material absorbs in the best way. Silicon is the most common material in solar cells because the amount of energy required to excite the electrons in it is close to the wavelength of visible light. However, solar cells composed of a single material have a maximum efficiency of only 31 percent - a limitation that comes from the fixed amount of energy they are able to absorb.

In solar cells based on quantum dots this limitation does not exist and therefore they are able to be much more efficient. The energy levels of the electrons in semiconductor quantum dots depend on their size - the smaller the dot, the more energy is required to excite the electron and raise it to a higher level.

Thus, the quantum dots can be tuned to absorb a certain wavelength of light simply by changing their size. They can also be used to build more complex solar cells that include more than one type of quantum dot of a defined size, which will allow the reception of a large number of wavelengths.

The researchers coated the titanium dioxide semiconductor inside the quantum dot-based solar cell with a very thin monolayer of organic molecules. These molecules organized themselves independently, that is, the interrelationships between the molecules caused them to organize together in an orderly manner. The quantum dots were placed at the interface between the organic layer and the semiconductor. The researchers tried a number of different organic molecules in order to examine which is the best substance for increasing the efficiency of the cells.

The researchers discovered that the particular type of molecules does not matter - the mere presence of an organic monolayer with a thickness of less than a nanometer was enough to triple the efficiency of the solar cells. "We were surprised by this result - we believed that the semiconductor would be extremely sensitive to the particular type of molecules," said the researcher.

The researcher adds and says that the result actually made sense in retrospect, and the researchers developed a new model - the dependence is on the length of the molecule, and not on the specific nature. Molecules that are too large do not allow the quantum dots to react properly with the semiconductor.

The researchers' theory claims that from the moment the solar energy creates an electron-hole pair, the thin organic layer helps separate them, preventing them from recombining and being wasted. The researchers have not yet improved the performance of their solar cells, and so far they have achieved an efficiency of only 0.4 percent. And yet, the researchers can change a number of characteristics in the cell, and indeed, once they do this, the threefold increase in efficiency, which results from the presence of the thin organic layer, will be much more significant.

The lead researcher explains that the quantum dots she is currently using, consisting of the material cadmium sulfide, are not ideal for solar cells and the researchers plan to test other materials. In addition, they plan to examine other molecules for the preparation of the organic layer, and to change the design of the solar cell in order to try and obtain a greater amount of light absorption and thereby produce a greater electric charge.

The news about the study

14 תגובות

  1. The costs of the raw materials are high (also there is excess demand in the market in recent years due to subsidies to private/institutional investors from governments such as Germany, USA, Italy... and also Israel in the last two years). There are very few companies that work vertically - vertically integrated on the entire process from the production of polysilicon to the panel.
    So although a competitive market is created from the multitude of companies that produce each process, transportation costs and long-term contracts of this and that also create high pricing.
    Just to be honest, most of the cells are made from silicon poly which costs around 70-80 dollars per kg. The manufacturer's price for a solar cell is around $1.1-1.3 per watt. (Panel around 1.3-1.5€ per watt)

  2. "We were surprised by this result..." In other words, the model we built that was based on existing knowledge was not correct from a practical point of view, so in my opinion it is not worth investing much in theories. You should always combine the practical with the theoretical, a small experiment saves years of theories that may turn out to be "surprising" in the first small experiment!
    Good luck, their success is everyone's success!

  3. Avishai:
    Even the energy absorbed by the solar cells does not stop reaching the earth. It simply does work before dissipating as heat and radiation instead of dissipating straight away.
    Therefore there is no such thing as "overexploitation".
    On the other hand, in principle it is possible to cause ecological damage if solar cells are spread over areas where animals and plants live because they also sometimes use solar energy

  4. Yehuda:
    You don't get a patent for what you do, but for how you do it.
    Therefore your words are not correct.

  5. Lani just a question
    A breakthrough as it is called is only the beginning of a long tedious road and sometimes even destined for commercial failure.
    But when so much money and good minds and serious entrepreneurs such as Shai Agassi are pushing for realization
    I am convinced that it is a matter of a few years until you feel the change.
    The rate of increase in the amount of solar electricity also increases so the change increases
    In 2008, for example, a total of 0.02% of humanity's energy consumption came from solar energy (Wikipedia)
    In another article it is claimed that 7% of all energy in the world was produced from renewable sources
    A little optimism and patience 🙂

  6. I read on this site (almost on Monday and Thursday) about so many breakthroughs in the field of solar cells, how come they haven't replaced oil and coal energy yet? Where are all these breakthroughs manifested practically in the field?

  7. The sun supplies the earth with energy of about 10 to the 24th power of joules
    The human race uses about 10 to the 18th power of joules
    (Data according to Wikipedia)
    So from a global point of view, even if all human energy needs come from the sun, it still won't change much the amount of energy that reaches the earth as it is (a difference of six orders of magnitude - a millionth of what the sun provides).

  8. Peace,
    I wanted to know if there are any studies on the environmental effects of "excess" utilization of solar energy?

  9. What a beauty. Discover another economical way to make solar cells.

    In the last three years they have discovered many methods that sound economical and will lower costs.

    I am impatiently waiting for a significant discount in the field.
    Unfortunately, I only bought two solar panels, and I wish the price would drop so I could buy more.

  10. A situation has reached that even if there is nothing significant for the researchers, they prefer to publish so that they will always state that they were the first. For example
    Extraterrestrial life has never been discovered. it is known. But if they do find out, then NASA will insist that it published it first in the story about the meteorite that "came" from Mars, which is known to be a very problematic proof.
    Here, too, in the publication of Stanford University, it is about a coating that will add to the efficiency of a photoelectric cell, in fact without the ability to prove that this is so.
    In short, an exploded title without anything real after it.
    Of course, someone else will not be able to patent it because it has already been said, and if they do, they will have to reach an agreement with Stanford University, the publisher of the article.
    Good Day
    Sabdarmish Yehuda

  11. Liyat Yosef, greetings.
    Indeed, your bewilderment is justified and understandable.
    However, it must be understood that the source of this news is in the spokesmen's department of the universities and private companies, therefore the advantages and not the disadvantages are emphasized.
    Beyond that, many more scientific details can be found in the article that is usually published following the discovery. A link to the source of the article appears in every news item of the scientist.

  12. to Ren,

    I'm not an expert but I'm pretty sure it's a combination of raw material with a high degree of cleanliness.

    To the writer, the researchers presented a utilization rate of 0.4 percent and claim that it is possible to reach a utilization rate of approximately 30-40 percent (which is impressive). But no such results were presented. Did the explosive title dazzle you and you gave up on the skeptical approach (which is the heart of science)? It's worse when you read the sentence:

    "Indeed, once they do this, the threefold increase in efficiency, which results from the presence of the thin organic layer, will be much more significant."

    A sentence that opens with the word "and indeed" should also contain results that support the previous sentence.

  13. ask me a question:
    What makes solar cells expensive?
    The production cost or the raw material?

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