Physicists at the University of Warwick found a new way that could literally squeeze more power out of solar cells by physically deforming each of the crystals in the semiconductors used by photovoltaic cells.
The study, led by Professor Marin Alexe and his team Ming-Min Yang, and Dong Jik Kim in the University of Warwick’s Department of Physics, first looked at the physical constraints on the current solar cells with absolute limit on their efficiency. Known as Shockley-Queisser Limit means only a maximum of 33.7% of sunlight can ever be turned into electricity. The anomalous photovoltaic effect has very low power generation efficiency and never used in practical power-generation systems.
The Warwick team worked on semiconductors that are effective in commercial solar cells so as to manipulate or push them in some way so that they too could be forced into a non-centrosymmetric structure and possibly benefit from the bulk photovoltaic effect.
For their experiment, they decided to push such semiconductors into shape using conductive tips from atomic force microscopy devices to a "nano-indenter" which they then used to squeeze and deform individual crystals of Strontium Titanate (SrTiO3), Titanium Dioxide (TiO2), and Silicon (Si).
They found that all three could be deformed to give a non-centrosymmetric structure and then able to give the bulk photovoltaic effect. Professor Marin Alexe from the University of Warwick said:"Extending the range of materials that can benefit from the bulk photovoltaic effect has several advantages: it is not necessary to form any kind of junction; any semiconductor with better light absorption can be selected for solar cells, and finally, the ultimate thermodynamic limit of the power conversion efficiency, so-called Shockley-Queisser Limit, can be overcome."
He described that there are engineering challenges but it should be possible to create solar cells where a field of simple glass based tips (a hundred million per cm2) could be held in tension to sufficiently de-form each semiconductor crystal. If such feat is possible and even a single percentage point of efficiency is added, it would be of immense commercial value to solar cell manufacturers and power suppliers.
This is an artists impression of squeezing more power out of solar cells by physically deforming each of the crystals in the semiconductors used by photovoltaic cells.(CREDIT: University of Warwick/Mark Garlick)