Stabilising perovskite solar cells

Perovskites were long considered the Ugly Duckling of photovoltaics. Modest energy efficiencies soon enough dimmed the initial enthusiasm for the potential of cheap and printable solar cells. But then, the energy efficiencies of perovskite solar showed a steep rise. Publications show a quick progress from an initial 3.9% in 2009, and 10% in 2012 to over 20% last year. The ‘ugly duck’ has taken off.

This rapid development motivated Hairen Tan, former PhD student of the Photovoltaic Materials and Devices group at the Faculty of Electrical Engineering, Mathematics and Computer Sciences, to choose perovskites as his new research field. He applied for a job interview with Professor Sargent from the University of Toronto, where he was offered a postdoctoral position in May 2015. He left for Toronto in October 2015, shortly after the defence with Cum Laude of his thesis ‘Materials and Light Management for high-efficiency thin film silicon solar cells’. The Rubicon grant that he applied for in August 2014 was awarded after he had moved to Toronto and will start from March 2016 until March 2018.

In Toronto, Tan will be working on resolving the main weakness of perovskite solar cells: their instability. Not only do they disintegrate under the influence of moisture, but also heat and light will eat away at the cell’s stability and performance. These are unfavourable characteristics for devices that are meant to be on the roof and stay there in any kinds of weather.

The solution he will investigate is to replace the conventional 3D crystal structure by a stack of layered lattices. He hopes to make the quasi 2D-material hydrophobic by putting organic molecules in-between the layers of perovskite material. Not only should the hydrophobic organic molecules keep the water out, but it should also make the crystal structure more heat- and light-resistant since the formation energy is higher (hence, to break the structure costs more energy as well).

After the Rubicon project, Tan would prefer to take on a faculty position at a university. That could mean going back to Europe (where the number of open positions is low) or back to China where he did his master’s degree. “The government is keen to attract postdocs abroad back to China and offers attractive working conditions and excellent research facilities”, said Tan.