The solution based on ‘single fission’ helps increase photovoltaic cell efficiency
In order to soon achieve the goal of net zero emissions, the scientific community is trying to find solutions to improve PV battery cell efficiency. One of the "highlight" studies is a new development from singlet fission technology by Australian scientists, currently being tested.
According to the Australian online solar energy news site (PMAC): The research team at the University of New South Wales (UNSW) is currently conducting research and has discovered that materials undergo singlet fission. Single-SF) provides an interesting and effective solution to exploit the entire solar spectrum, increasing the efficiency of solar cells.
The efficiency of converting solar energy into electricity of photovoltaic cells (PV cells) is often low, currently only reaching 20 to 25%. Silicon technology currently dominates the photovoltaic market, accounting for 90% of all commercially available PV, but silicon PV does not and cannot exploit the entire solar spectrum. Silicon solar cells are thermodynamically limited, converting only 30% of sunlight into useful electricity. The two main loss mechanisms are: Transmission of photons with energy less than the band gap (1,1eV) and heat generation from photons with energy exceeding the band gap. prohibited zone.
Because silicon solar cells are thermodynamically limited, converting only 30% of the light spectrum, scientists are working on devices that can be used in tandem.
According to UNSW: The best path to increasing solar cell efficiency step by step is to build on the success of silicon. UNSW has developed a parallel ‘something on silicon’ device. The concept is like using higher bandgap absorbers in a subcell, which can be electronically (2- or 3-terminal parallel) or mechanically (4-terminal parallel) coupled. on top of the silicon cell. Promising materials include organometallic halide perovskites, III-V inorganic semiconductors, and chalcogenides.
However, materials that undergo single fission offer another avenue to increase the use of the solar spectrum. Normally, the photoelectric effect is a one-to-one process. One photon gives us many electrons. UNSW calls this “external quantum efficiency”, or EQE, which is 100%. When exploiting singlet fission, we can extract two electrons for each photon absorbed – which is possible with an EQE of 200%, and in fact, the EQE exceeds 100%.
To put it more simply, the singlet fission or SF mechanism, in which one photon excites two electrons, has the advantage of overcoming the current disadvantages of photovoltaic cells. Singlet fission is a spin-permitting process, unique to photomolecular physics, whereby an excited state of a singlet is converted into two triplet states.
Normally, when a photon from sunlight is absorbed by a molecule, the energy level of one of the electrons in the molecule is markedly increased. By absorbing a photon, an organic molecule is thus converted into a higher energy state. Electricity can then be generated in solar cells from this energy temporarily stored in the molecule. The optimal scenario in conventional solar cells is that each photon produces an electron as a charge carrier. However, if selected chemical compounds are used, two electrons from neighboring molecules can be converted to a higher energy state. So a photon creates two excited electrons, which in turn can be used to create an electric current, or two created from one. This process, called SF or singlet fission, greatly increases the efficiency of solar cells.
Through testing, UNSW found that the beneficial effect was a reduction in operating temperature, thereby extending the life of the cell by an estimated 3,7 years. Because singlet fission makes efficient use of high-energy photons, less heat is generated than with current technologies, which in turn has the effect of cooling the underlying silicon module. This cooling effect will occur in all silicon-based devices but is most significant in singlet fission devices, with an estimated temperature drop of 2°C (according to the IEC61212 standard).
Like parallel cells, the best route for singlet fission is to use it as a top layer on a silicon stem cell. Unlike other parallel concepts, this can be done with minimal changes to the silicon architecture, reducing both complexity and cost. Furthermore, in some single fission architectures, UNSW has avoided the problem of optimizing the electrical conductivity of the new material, by sourcing the electrical transport to the silicon stem cell externally. This eliminates the need for voltage/current matching between the singlet fission and the silicon layers.
Finally, the materials used for singlet fission are typically small organic molecules or polymers, similar to those that have been developed in organic light-emitting diodes (OLEDs). Therefore, large-scale production of singlet fissile material will be able to take advantage of existing chemical synthesis infrastructure. This means that the efficiency benefits of the singlet/silicon fission approach can be achieved without significantly increasing PV module costs. The two main classes of molecules being studied include polychromatic hydrocarbons – including light-stable paint pigments – and polymers that have been found useful in existing organic photovoltaic technologies.
According to PMAC: In the study, scientists created a molecular dimer from two pentacene units. This hydrocarbon is considered a promising candidate for single fission use in solar cells. They then exposed the liquid to light and used various spectroscopic methods to study photophysical processes in the molecule. This helps researchers gain a deeper understanding of the mechanism behind single-molecule fission in molecules.
First: They succeeded in demonstrating that coupling to a higher load transfer state is essential for highly efficient SF.
Second: The model for single or singlet fission has been determined.
And finally, demonstrate that the effectiveness of SF clearly correlates with how strongly the two pentacene sub-units are combined.
There are some limitations to singlet fission. As mentioned above, the singlet fission approach is in the early stages of development, so it still contains both excitement and obstacles that need to be resolved to soon have a product for application. According to UNSW, this is a major milestone towards the use of SF-based photovoltaic systems to generate electricity.
According to Vietnam Energy Magazine