Since the ‘development’ in 2009 of a highly energy-efficient class of solar-cell materials known as HOIPs — hybrid organic-inorganic perovskites — researchers have been trying to understand exactly how these materials ‘tick’ at the molecular level, in order to improve the durability of their performance.
HOIPs are exceptionally lightweight, flexible (they can be painted onto substrates, such as paper and plastic), inexpensive and nearly as efficient as traditional silicon-based cells at converting light into electricity — characteristics that mean HOIPs could eventually power homes, lightweight vehicles such as drones and spacecraft, and provide ‘ready electricity’ to backpackers or military personnel in remote locations.
However, HOIPs currently lack stability in their crystal structure, causing fairly rapid degrading of their energy-conversion efficiency, especially in fluctuating temperatures.
The problem is that, inside a solar cell, light excites electrons, which is what makes these materials work, but the electrons don’t last long enough in the excited phase to produce power over the long term.
In a paper recently published in the journal
Proceedings of the National Academies of Sciences, physicist Seung-Hun Lee and chemical engineer Joshua Choi (researchers at the University of Virginia) detailed how rotating molecules in HOIPs allow charged electrons to endure, rather than dissipate, resulting in the higher energy-conversion efficiency of these materials.
Mr Choi said: “This finding sets us on the path to better manipulating HOIPS for greater efficiency, as well as for longer-lasting efficiency under changing conditions.”
Mr Lee said: “The trick will be finding ways to maximise the effect of these molecular rotations to extend the electron lifetimes.”
They used a combination of advanced microscopic detection devices and measurement techniques with high-performance computer modelling to make their minute and detailed observations of the changing molecular structures of the materials.
They say this work will lead to more readily identifying and developing new materials that maintain efficiency over a wider range of temperature changes.