Quantum dot solar cell first exceeds 100% quantum efficiency

According to the report of the American Physicist Organization Network on December 16 (Beijing time), the National Renewable Energy Laboratory (NREL) has developed a new quantum dot solar cell that is activated by photons emitted from the high-energy region of the solar spectrum. At the same time, there will be a photocurrent with an external quantum efficiency of up to 114%. The latest study published in the December 16th issue of Science laid the foundation for scientists to develop third-generation solar cells.

When photons are incident on the surface of the solar cell, part of the photons will excite the photosensitive material to generate electron-hole pairs and form a photocurrent. The ratio of the number of electrons generated to the number of incident photons at this time is called the external quantum efficiency of the photocurrent. To date, no solar cell has exhibited an external quantum efficiency of more than 100% under the irradiation of light in the solar spectrum.

The NREL team has achieved this for the first time on quantum dot solar cells. They obtained a 114% external quantum efficiency on a stacked quantum dot solar cell. The cell consists of a glass with a retroreflective coating (which contains a thin layer of transparent conductor), a layer of nanostructured zinc oxide, a layer of treated lead selenide quantum dots, and a thin layer of gold used as electrodes. .

Solar photons produce over 100% of the external quantum efficiency based on the carrier-multiplication (MEG) process, by which a single absorbed high-energy photon can excite multiple electron-hole pairs. For the first time, the NREL team demonstrated MEG in the photocurrent of quantum dot solar cells. Scientists can use this to improve the conversion efficiency of solar cells. The results show that the photoelectric conversion efficiency of the new quantum dot solar cell is higher than 4.5% under simulated sunlight irradiation. At present, this type of solar cell has not yet been optimized, so its energy conversion efficiency is relatively low.

Compared with traditional solar cells, MEG in quantum dot solar cells can increase the theoretical thermal energy conversion efficiency of the battery by 35%. Quantum dot solar cells can also be manufactured using a roll-to-roll process that is inexpensive and yields high. One advantage is that the manufacturing cost per unit area is very low, and scientists call it the third generation (next generation) of solar cells.