Polarizing Polymers for Photovoltaic PowerCategory: Science & Technology
Posted: June 15, 2012 03:06PM
When most people think about how semiconductors work they think in terms of electrons moving around, but this is not completely accurate. Yes electrons do move around but researchers are finding it is also important to understand positively charged hole left behind. The electron-hole pair constitutes a quasiparticle called an exciton, and researchers are working to better understand how to control them. Now those at Argonne National Laboratory are using some of this knowledge to improve polymer, or organic, solar cells.
Like any semiconductor-based solar cell, when light hits the polymer solar cell it excites electrons out of their atoms, creating excitons. The excited electrons then travel from the cell, through a circuit, and back to the cell where it recombines with the hole. At least that is what we want to happen, but sometimes the electron does not escape the pull of the positive hole and the exciton collapses, causing the energy to be lost. Fortunately though, the properties of excitons in polymer solar cells can be controlled, because the polymer can be changed, unlike silicon solar cells, that all use silicon.
The researchers determined that it should be possible to polarize the excitons within the polymer. This means the electron and hole in a single exciton start further apart. That makes it much less likely for the exciton to collapse before the electron goes through the circuit. Polymer solar cells still are not as efficient as silicon-based cells, but they remain the cheaper option.