The conductivity of organic solar cells ushered in a new breakthrough

Due to an accidental discovery in the experiment, the slow-developing organic solar cell industry finally ushered in a turning point, and its energy conversion efficiency has made a major breakthrough. This breakthrough comes from the process of electrons moving in the layer of fullerene molecules (commonly known as “buck balls”). Scientists at the University of Michigan discovered this when experimenting with organic solar cell architectures. At that time, researchers added two layers of fullerene molecules to the electricity-generating layer of the organic battery, and photons collided in the electricity-generating layer to drive electron transport.

Due to an accidental discovery in the experiment, the slow-developing organic solar cell industry finally ushered in a turning point, and its energy conversion efficiency has made a major breakthrough. This breakthrough comes from the process of electrons moving in the layer of fullerene molecules (commonly known as “buck balls”). Scientists at the University of Michigan discovered this when experimenting with organic solar cell architectures. At that time, researchers added two layers of fullerene molecules to the electricity-generating layer of the organic battery, and photons collided in the electricity-generating layer to drive electron transport.

They found that electrons move more freely in the fullerene layer, travel farther, and also create an “energy well” (technically called a potential well), which prevents the electrons from escaping. When these electrons are transmitted in the fullerene molecular layer, the transmission distance can reach a few centimeters (the current organic battery can only move a few hundred nanometers at most), so it can generate a larger current.

Why is this breakthrough so important

As we all know, the conductivity of organic batteries is very weak, because there are many loose bonds between the various molecules of organic materials. There is no high-efficiency conduction pipeline between molecules, so electrons are often trapped and can only move a few hundred nanometers at most. For organic solar cells, the capture of electrons is the main obstacle that limits the distance the electrons travel. If electrons can move freely without obstruction, they can travel farther. This is true for all solar cells, but organic cells make the movement of electrons more challenging. Because the electrons did not travel far enough before being captured, they could not enter the circuit. This obstruction reduces the conductivity of the battery, and as there are fewer and fewer free-flowing electrons, the energy conversion efficiency also decreases. Therefore, the energy conversion efficiency of organic solar cells composed of polymers and other non-metal semiconductors is only 13.1%. This level of efficiency is simply not comparable to that of silicon-based inorganic solar cells, which have an energy conversion efficiency of 26.6% and are currently widely used in solar panels.

However, some of the advantages of organic solar cells still have value for further research. For example, in addition to the use of simpler polymer processing technologies that have the potential to reduce costs, organic solar cells are also thinner, more flexible, and more transparent. These characteristics are essential for the efficient conversion of sunlight into electricity. In addition, when constructing net zero energy buildings (NZEB) or retrofitting existing structures to improve energy efficiency, companies can integrate organic solar cells into the structure itself, such as roofs and walls. In these places, the bulky and inflexible silicon-based inorganic solar cells are neither practical nor feasible. In addition, these organic solar cells have other advantages, for example, they have a variety of colors and configurations, and have better aesthetic effects.

Breakthrough in conductivity

Obviously, we need to find some ways to fully realize the potential of organic solar cells, and breakthroughs in conductivity are the key point. According to an article from the University of Michigan titled “semiconductor Breakthrough May Be a Game-Changer for Organic Solar Cells”, researchers added a fullerene molecular layer to the electricity-generating layer of organic solar cells, and photons are in the electricity-generating layer. Impact to drive electron transmission. They used a common technique called “vacuum thermal evaporation” to layer C60 fullerenes, each layer composed of 60 carbon atoms. They found that electrons can move freely in the fullerene layer instead of being trapped in loose bonds between organic molecules.

Interestingly, fullerenes are considered excellent acceptor molecules due to their variable hybridization state, re-hybridization ability, and curved topology. (It is worth noting that since the application of fullerenes in solar cells was discovered, a new type of high-efficiency solar cells has appeared, now called non-fullerene acceptor (NFA) organic solar cells. Leenes have similar electron-accepting properties, but they are obviously non-fullerene molecules.) Fullerenes are also electron-limited materials, and they contain potential (ie, quantum) wells. Once the electron falls into the potential well of the fullerene molecule, it is difficult to get out. Using the electron blocking layer embedded in the fullerene layer can prevent any electrons from leaving and recombining with holes, forming an additional barrier.

The only way electrons can influence the area outside the potential well is through electron tunneling. If the quantum wells are placed side by side, that is, fullerene molecules can be adjacent to each other in a layer, then they can form a so-called “superlattice.” If the distance between the quantum wells is less than the range of the electron tunneling wave function, the electron wavelengths can overlap and establish a connection between the potential wells, allowing electrons (and current) to flow. Therefore, by trapping electrons in the fullerene layer, the intermolecular potential wells allow the electrons to flow unimpeded, without the risk of being trapped.

Similarly, because electrons can move freely and cannot recombine with holes in the electricity-generating layer, electrons can move farther, reaching a few centimeters, not just a few nanometers, thereby generating a larger current. Therefore, as mentioned above, there may now be a greater current, not because a single electron carries more energy, but because there are more carriers (that is, electric charge) flowing in the circuit. Ultimately, the specific current (and efficiency) increase in organic solar cells depends ON the number of electrons flowing in the system before and after fullerene is added.

Impact on the industry

Researchers at the University of Michigan admitted that this discovery is only the beginning, and more work needs to be done to improve the design of organic solar cells, especially to study what other organic materials can become excellent Electronic conductors. Stephen Forrest, an engineering professor at the University of Michigan, predicts that it may take up to 10 years to develop a mainstream organic solar cell solution.

However, the discovery of fullerenes finally paved the way for organic materials to be used to make efficient and transparent solar cells. For example, solar cell manufacturers can shrink the conductive electrodes of solar cells into an invisible grid, and combine other characteristics of organic solar cells to laminate organic materials on the surface of any object. Due to the low processing cost of polymers used in organic solar cells, these solutions can achieve reasonable prices in a variety of applications. But perhaps the biggest breakthrough brought about by this discovery is that more discoveries will lead to more progress.

Due to an accidental discovery in the experiment, the slow-developing organic solar cell industry finally ushered in a turning point, and its energy conversion efficiency has made a major breakthrough. This breakthrough comes from the process of electrons moving in the layer of fullerene molecules (commonly known as “buck balls”). Scientists at the University of Michigan discovered this when experimenting with organic solar cell architectures. At that time, researchers added two layers of fullerene molecules to the electricity-generating layer of the organic battery, and photons collided in the electricity-generating layer to drive electron transport.

They found that electrons move more freely in the fullerene layer, travel farther, and also create an “energy well” (technically called a potential well), which prevents the electrons from escaping. When these electrons are transmitted in the fullerene molecular layer, the transmission distance can reach a few centimeters (the current organic battery can only move a few hundred nanometers at most), so it can generate a larger current.

Why is this breakthrough so important

As we all know, the conductivity of organic batteries is very weak, because there are many loose bonds between the various molecules of organic materials. There is no high-efficiency conduction pipeline between molecules, so electrons are often trapped and can only move a few hundred nanometers at most. For organic solar cells, the capture of electrons is the main obstacle that limits the distance the electrons travel. If electrons can move freely without obstruction, they can travel farther. This is true for all solar cells, but organic cells make the movement of electrons more challenging. Because the electrons did not travel far enough before being captured, they could not enter the circuit. This obstruction reduces the conductivity of the battery, and as there are fewer and fewer free-flowing electrons, the energy conversion efficiency also decreases. Therefore, the energy conversion efficiency of organic solar cells composed of polymers and other non-metal semiconductors is only 13.1%. This level of efficiency is simply not comparable to that of silicon-based inorganic solar cells, which have an energy conversion efficiency of 26.6% and are currently widely used in solar panels.

However, some of the advantages of organic solar cells still have value for further research. For example, in addition to the use of simpler polymer processing technologies that have the potential to reduce costs, organic solar cells are also thinner, more flexible, and more transparent. These characteristics are essential for the efficient conversion of sunlight into electricity. In addition, when constructing net zero energy buildings (NZEB) or retrofitting existing structures to improve energy efficiency, companies can integrate organic solar cells into the structure itself, such as roofs and walls. In these places, the bulky and inflexible silicon-based inorganic solar cells are neither practical nor feasible. In addition, these organic solar cells have other advantages, for example, they have a variety of colors and configurations, and have better aesthetic effects.

Breakthrough in conductivity

Obviously, we need to find some ways to fully realize the potential of organic solar cells, and breakthroughs in conductivity are the key point. According to an article from the University of Michigan titled “Semiconductor Breakthrough May Be a Game-Changer for Organic Solar Cells”, researchers added a fullerene molecular layer to the electricity-generating layer of organic solar cells, and photons are in the electricity-generating layer. Impact to drive electron transmission. They used a common technique called “vacuum thermal evaporation” to layer C60 fullerenes, each layer composed of 60 carbon atoms. They found that electrons can move freely in the fullerene layer instead of being trapped in loose bonds between organic molecules.

Interestingly, fullerenes are considered excellent acceptor molecules due to their variable hybridization state, re-hybridization ability, and curved topology. (It is worth noting that since the application of fullerenes in solar cells was discovered, a new type of high-efficiency solar cells has appeared, now called non-fullerene acceptor (NFA) organic solar cells. Leenes have similar electron-accepting properties, but they are obviously non-fullerene molecules.) Fullerenes are also electron-limited materials, and they contain potential (ie, quantum) wells. Once the electron falls into the potential well of the fullerene molecule, it is difficult to get out. Using the electron blocking layer embedded in the fullerene layer can prevent any electrons from leaving and recombining with holes, forming an additional barrier.

The only way electrons can influence the area outside the potential well is through electron tunneling. If the quantum wells are placed side by side, that is, fullerene molecules can be adjacent to each other in a layer, then they can form a so-called “superlattice.” If the distance between the quantum wells is less than the range of the electron tunneling wave function, the electron wavelengths can overlap and establish a connection between the potential wells, allowing electrons (and current) to flow. Therefore, by trapping electrons in the fullerene layer, the intermolecular potential wells allow the electrons to flow unimpeded, without the risk of being trapped.

Similarly, because electrons can move freely and cannot recombine with holes in the electricity-generating layer, electrons can move farther, reaching a few centimeters, not just a few nanometers, thereby generating a larger current. Therefore, as mentioned above, there may now be a greater current, not because a single electron carries more energy, but because there are more carriers (that is, electric charge) flowing in the circuit. Ultimately, the specific current (and efficiency) increase in organic solar cells depends on the number of electrons flowing in the system before and after fullerene is added.

Impact on the industry

Researchers at the University of Michigan admitted that this discovery is only the beginning, and more work needs to be done to improve the design of organic solar cells, especially to study what other organic materials can become excellent electronic conductors. Stephen Forrest, an engineering professor at the University of Michigan, predicts that it may take up to 10 years to develop a mainstream organic solar cell solution.

However, the discovery of fullerenes finally paved the way for organic materials to be used to make efficient and transparent solar cells. For example, solar cell manufacturers can shrink the conductive electrodes of solar cells into an invisible grid, and combine other characteristics of organic solar cells to laminate organic materials on the surface of any object. Due to the low processing cost of polymers used in organic solar cells, these solutions can achieve reasonable prices in a variety of applications. But perhaps the biggest breakthrough brought about by this discovery is that more discoveries will lead to more progress.

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