This morning saw a solar breakthrough at the National Renewable Energy Laboratory (NREL), where researchers created a quantum dot solar device that has a higher energized particle percentage output than its energized particle input. The photocurrent of a solar device — photocurrent shows the efficiency of a solar cell — is expressed as a percentage and is found by measuring the number of electrons flowing per second out of the solar cell divided by the number of photons per second of an energy entering the solar cell. NREL researchers have developed a solar cell that has a photocurrent of 114%, which is the most efficient ratio ever seen before.
The key to these über efficient solar devices is Multiple Exiton Generation (MEG). This process says that if a solar cell absorbs a photon that has enough energy needed, that one photon entering the solar cell can produce more than one electron-hole pair exiting the solar cell (the electron-hole pair is the unit of energy generated by the solar panel that translates into energy transmitted by the device). Researchers believe this discovery could significantly increase the efficiency and cost effectiveness of solar power over fossil fuel power.
The cell used to achieve the photocurrent of 114 was a layered cell which consisted of antireflection-coated glass, a transparent conductor, a nanostructured zinc oxide layer, a quantum dot layer and a thin layer of gold on top. In addition to being highly efficient — we might even say overefficient — at translating energy in to energy out, the quantum dot solar cell in question was also highly efficient at absorbing solar energy as well. Many current solar cells only absorb a small amount of the photos that come in contact with them and therefore aren’t able to convert all of the sunlight that runs across their surface into electricity. This new solar cell was extremely efficient when it came to absorption. That coupled with the high photocurrent and a relatively low production cost could make this discovery a key to bringing solar energy’s cost down below that of nuclear energy and perhaps even the cheapest and dirtiest of them all, coal.