Doctoral dissertation

Dissertation: Knowledge on reaction kinetics is the key to design novel solar cells

Kirsi Virkki
The global carbon emissions need to be decreased dramatically in the next decades. In order to meet the climate targets, we need renewable and carbon-neutral energy sources. A dissertation at Tampere University studies the kinetics of chemical reactions inside solar cells in order to design more efficient solar cells.

The Sun is the ultimate source of clean, renewable energy for the needs of the mankind. Solar cells are one of the most promising carbon-neutral energy sources. They are especially suitable for small power plants in e.g. areas difficult to reach. In order to design novel solar cells, it is essential to obtain a deep understanding on the chemical reactions inside the cells. M.Sc. (Tech.) Kirsi Virkki has studied the kinetics of these reactions in her doctoral dissertation.

”Understanding the mechanisms in these reactions on a comprehensive level helps us to develop more and more efficient solar cells”, says Virkki.

Michael Grätzel was awarded with the Millennium Technology Award on the discovery of dye-sensitized solar cells in 2010. In her dissertation, Virkki has studied similar structures to those used in dye-sensitized solar cells. At the spotlight in the dissertation have been phthalocyanine dyes.

“Phthalocyanines are chemically and thermally stable and are thus suitable for solar cell applications. A downside with these compounds is the molecular stacking or aggregation that makes the solar cells less efficient. I concentrated especially on reducing the aggregation of the phthalocyanine dyes”, Virkki describes.

Virkki studied two different methods for reducing the aggregation, and the effect of these methods on the reaction kinetics in solar cell samples.

“The results indicate that reducing the aggregation indeed increases the solar cell efficiencies, accounting for the light absorbed by the devices”, Virkki summarizes. “This knowledge directs the development of novel solar cell dyes.”

Kirsi Virkki (32), originally from Savonlinna, works as a researcher at the Chemistry and Advanced Materials research group at Tampere University.

The doctoral dissertation of M.Sc. (Tech.) Kirsi Virkki in the field of chemistry titled Photoinduced Charge Transfer Processes at Organic-Semiconductor Interfaces will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University at 12.00 on Friday 24.5.2019 in auditorium Pieni Sali 1 of the Festia building.  The Opponent will be Associate Professor Maria Abrahamsson from Chalmers University of Technology in Gothenburg. The Custos will be professor Nikolai Tkachenko from the Faculty of Engineering and Natural Sciences.

The dissertation is available online at