Advances in solar photovoltaics
Advances in solar energy happen constantly. It’s a shame that they would not have occurred before or had invested more in this type of research a few years ago. If so we would have sold cheap solar energy. It takes a long time since I have an idea, it is tested and then finally (if it works) is marketed.
It is also unfortunate that issue is so politicized and subject to all sorts of obscure interests. We need cold, clear accounting analysis that allow us to make good decisions, even on a personal level. It seems, however, which is approaching the day where every individual can become self-sufficient power at a reduced price and independent power companies. We will see below some progress and results on this field have been made public during the last week.
Xiaoyang Zhu University of Texas at Austin and his colleagues have succeeded in demonstrating that it is possible to increase the efficiency of conventional cells significantly [1], [2]. Has shown that you can double the number of electrons collected when a photon impinges on semiconductors. Usually some of the electrons produced during the photovoltaic phenomenon are lost and only produce heat instead of useful electricity. This is even more critical in photovoltaic plastics, which are performing poorly. But on the other hand, production of such photocells is dirt cheap, so if it could increase its efficiency and life would have solved the problem of solar energy.
Maximum performance in silicon has been achieved so far is 31% in the laboratory, if you managed to recover these “hot electrons” that are normally lost as heat could achieve yields of 66%.
Zhu has already shown that these electrons could capture using nanocrystals, has now found an alternative method. Apparently there are quantum states “shadow”, called multi-excitons, for which the electrons can be captured effectively in certain types of semiconductors. In the experiments the multiexcitón behaved as an efficient source of two electrons through the use of fullerene.
Basically the high-frequency photons have more energy, but it can not deposit their energy in the form of electrons because the energy gap of the semiconductor has a specific energy and can not convert more energy than the trench itself. Cells are used in semiconductor multilayers of different types to absorb primarily a specific frequency band and so take advantage most of the solar spectrum, but are complex. This method allows high-energy photons absorbed and efficiently converted into electricity through a process of two electrons instead of just one.
According to this researcher if exploited this mechanism cells can be obtained with a yield of 44% without needing a hub.
Arthur Nozik, National Renewable Energy Laboratory in Golden (Colorado) and his collaborators have reported the first solar cell that produces a photocurrent with external quantum efficiency greater than 100% when excited by photons of the most energy spectrum [ 3], [4], [5]. This is a multi-multiexcitón result similar to the above.
The photocurrent, which is normally expressed as a percentage, is the number of electrons flowing per second in the external circuit of the photocell divided by the number of photons of a specific energy entering the cell. This result obtained in this case, 114% of photocurrent indicates that electrons manage to produce more photons strike the cell.
In this case they used selenium grains (quantum dots of 1-20 nm) “decorated” with organic molecules in order to prevent clumping together and losing their properties. They have achieved yields of 5% using only a small part of the performance spectrum that is equivalent to 20% if extrapolated to the rest. But anyway, they get to collect 30% more load than usual, which is the key to progress. This makes expected future developments on this idea that ultimately have practical application.