Xinhua News Agency, Beijing, July 5 (Xinhua) - U.S. researchers have designed a new type of silicon solar cell. By changing the passivation layer material, the energy conversion efficiency of silicon solar cells can be increased from about 29% to 35%.
Massachusetts Institute of Technology (MIT) recently issued a bulletin that the new batteries are designed by its staff and colleagues from Princeton University and other institutions in the United States, using the principle of "single-state exciton fission" to enhance the use of high-energy photon energy.
In solar cells, photons excite material molecules to release electrons and generate electric currents. Usually a photon can only excite one electron, and the residual energy of a high-energy photon will be lost in the form of heat.
Previously, it has been found that in some organic materials, such as tetraphenyl, a molecule can absorb a high-energy photon and transfer part of its energy to another molecule, resulting in two electrons. This phenomenon is called "singlet exciton fission". In theory, two electrons can be obtained from a single high-energy photon by covering a layer of tetraphenyl on a silicon cell, but how to transfer the two electrons produced by "single-state exciton fission" to silicon is a key problem.
In order to ensure the efficiency and durability of the battery, the silicon material must have a passivation layer on the surface. Electrons generated in tetraphenyl must pass through the passivation layer to reach the silicon material. Current passivation layers are too thick for electron transfer capability.
The key of the new scheme is to passivate the silicon material with hafnium nitride. The thickness of passivation layer obtained is only 0.8 nanometer (1 nanometer equals one billionth of a meter), which allows more electrons to pass through. The results show that 1.3 electrons per photon absorbed by tetraphenyl can pass through the passivation layer of hafnium nitride and transfer to the silicon material.
The papers have been published in the British Journal Nature. Researchers say that the efficiency of new batteries is far from the theoretical limit and needs to be improved, but experiments show that the key steps are effective. The scheme does not introduce complex design and may make the battery thinner overall.