American researchers have designed a new type of silicon solar cell scheme. By changing the material of the passivation layer, the upper limit of the energy conversion efficiency of the silicon cell can be increased from about 29% to 35%.
The Massachusetts Institute of Technology recently issued a communiqué saying that the new battery was designed by its staff and colleagues from Princeton University and other institutions in the United States, using the "singlet exciton fission" principle to enhance the use of high-energy photon energy.
In a solar cell, photons excite material molecules to release electrons, generating electrical current. Usually one photon can only excite one electron, and the remaining energy of the high-energy photon will be lost in the form of heat.
Previously, it has been found that in certain organic materials such as naphtha, a molecule can absorb part of a high-energy photon and transfer part of the energy to another molecule, which eventually produces two electrons. This phenomenon is called "singlet exciton fission" ". Theoretically, covering a silicon cell with a layer of naphthacene can obtain two electrons with one high-energy photon, but how to transfer the two electrons generated by "singlet exciton fission" to silicon materials is a key problem.
In order to ensure battery efficiency and durability, the silicon material must have a surface passivation layer. The electrons generated in naphtha must pass through the passivation layer to reach the silicon material. Compared with the electron transfer ability, the current passivation layer is too thick.
The key to the new scheme is to passivate silicon materials with hafnium oxynitride. The resulting passivation layer is only 0.8 nanometers thick (1 nanometer equals one billionth of a meter), allowing more electrons to pass through. Studies have shown that for every photon absorbed by tetracene, an average of 1.3 electrons can pass through the passivation layer of hafnium oxynitride and be transferred into the silicon material.
Related papers have been published in the British "Nature" magazine. The researchers said that the efficiency of the new battery is far from the theoretical limit and needs to be improved, but the test proves that the key steps are effective. This solution does not introduce a complicated design and may make the battery thinner overall.
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