Little is known about the long-term stability of photovoltaic solar panels. Solliance/TNO researcher Mirjam Theelen has developed an experimental set-up in which the degradation of solar cells can be accelerated and the degradation monitored in real time. The experimental set-up has been well received in the photovoltaic world and is now being commercialised. On Friday 2 October, Theelen will defend her PhD thesis at TU Delft that is related to this subject.


Copper indium gallium selenide (CIGS) solar cells have a large potential for large-scale application, as they can be manufactured inexpensively and on flexible substrates.  In this way they offer extensive opportunities for product integration. It is the reliability of CIGS solar panels that is an important factor, as well as their price and efficiency, in determining the eventual price of electricity that is generated. Knowledge of the ageing mechanisms of the cells is therefore very important, both for the purpose of being able to calculate their lifespan correctly (relevant to the guarantee, for example) and for optimising their lifespan.

Lifetime tests

However, CIGS solar panels have only been produced on a large scale for a few years, and knowledge of their long-term stability is limited. The accelerated lifetime tests that are currently used for forecasting their lifespan can be insufficient. For this reason, Mirjam Theelen developed an experimental set-up during her PhD research, as part of the research programme M2i, in which the degradation of solar cells can be accelerated and the degradation monitored in real time.

According to Theelen, the experimental set-up has been well received in the solar cell world. Three SMEs from the Netherlands, led by Eternal Sun, are now going to optimise and commercialise the set-up. The test set-up will be kept at Solliance for further research and remain available as a test facility for third parties.

Ageing mechanisms

From a scientific point of view, this research has meant that the previously limited knowledge of the ageing mechanisms of CIGS cells has been greatly expanded. Among the discoveries are that elements such as sodium and potassium, which are added because they are essential for the high initial efficiency of the cells, can have a negative influence on their stability. Theelen, who works as a researcher at Solliance/TNO, did her PhD at TU Delft under Professor Miro Zeman from the Photovoltaic Materials and Devices section of the Faculty of Electrical Engineering, in collaboration with the University of Nantes in France.

She has now been invited to join the PVQAT, an international committee that determines the test guidelines for solar cell energy.


Solliance is a partnership between TNO (the Netherlands Organisation for Applied Scientific Research), Eindhoven University of Technology, Holst Centre, the Energy research Centre of the Netherlands, IMEC, the Forschungszentrum Jülich, TU Delft, and the University of Hasselt, and focuses on research and development of thin-film photovoltaic technologies. TU Delft joined the Solliance academic board earlier this year.

Materials innovation institute (M2i)

The PhD research is part of the research programme M2i. As independent network organisation M2i offers research in materials and advice to companies enabling product development through material innovation. Currently M2i runs about 100 research projects at different universities in the Netherlands and Europe and.

Further information

For further information you can contact Mirjam Theelen via tel. +31 6 468 474 34 and or Wendy Batist, press officer TU Delft via tel. +31 15 27 884 99 and

The full thesis is available at

Related press releases

Press release TU Delft, 30 January 2015