Researchers from the University of Sydney have developed what they term as a “photochemical upconversion” technique to increase the solar cells’ efficiency. This could potentially be up to a record breaking 40%.
Even though there has been a continued improvement in the overall efficiency of conventional silicon solar cells in the past few years, and this technology faces a natural theoretical limit at around 33%, still its potential cannot be underrated.
The laws of physics prevent solar cells to absorb light photons below a specific energy level. This means that at a certain point, low-energy light cannot be converted into electric power and is just lost. But researchers have now found a way to join two poor red photons and make from them a single energy-rich yellow photon, thus allowing them to harvest this part of the spectrum.
This means that the “photochemical upconversion” technology can now make it possible to harness electricity from a spectrum currently unused by conventional single p-n junction crystalline silicon solar cells.
The photochemical upconversion depends on two different types of molecules placed behind the solar cell in a solution to make a single high-energy photon from two low-energy photons.
The first type of molecule absorbs the energy-poor red photons; this prevents them from escaping and they are stored in a persistent state. The second type of molecule in the solution gets the energy transferred from the first after its persistent state has lasted long enough to facilitate this. The second organic molecule then gains an excited state.
When two such excited molecules encounter each other, one assumes a higher energy state while the other returns to the base state. The high energy state thus achieved is extremely short lived. This is because it sends off a single yellow photon of an energy that is high enough to be absorbed by the solar cell.
The photochemical upconversion technique was documented in detail in the Energy & Environmental Science journal earlier this year. The study was spearheaded by Associate Professor Schimdt of the University of Sydney. He developed the so-called “turbo for solar cells” in collaboration with partners at Helmholtz Center Berlin for Materials and energy.