Researchers at Aalto University have found that only a fraction of stability tests done on perovskite-based solar cells and dye-sensitized solar cells meet proper requirements. The team analyzed 261 aging tests conducted on such solar and saw major shortcomings in both how the results had been reported and how tests had been implemented. Tests lack common standards and should have been done in real-world conditions and in groups of several cells.

"In about half of the aging studies, the data was published only for one solar cell. Studying only one cell does not yield a sufficient amount of data to reliably compare how different materials age, that is, lose efficiency over time," says the team.

The researchers also found other deficiencies in the stability studies. Only a third of the tests reported the intensities of visible and UV light, the humidity and temperature. Most of the tests – around 52% – did not mention the intensity of the UV light. UV light is a significant stress factor for most types of solar cells, shortening the cells' lifetimes more than pure visible light.

About half of the aging tests had been performed solely in dark conditions. Only 15 tests had been conducted outdoors and three tests were made using modules comprising several cells connected together. This goes against the principle of testing the cells in conditions in which they will be used, which is a requirement for commercialization.

The inadequately reported test conditions reduce the reliability of the results and slow down the development of the new solar cell technologies. Aalto researchers hope that a more daring approach could be found in the field so that tests on aging could also be implemented in actual conditions in which the cells will also be used in energy production.

"The field needs common standards. High-quality, well-reported, and standardized tests would reinforce the confidence of industry and investors in the technologies". The researchers have written a detailed checklist for doing high-quality aging tests and how to take testing conditions into consideration and how to select the measurements to be carried out during testing.



The team also proposes organizing a series of conferences for establishing common guidelines and standards for aging tests. It will require close cooperation with other players in the field. For instance, in silicon cell research, the standards have been set by commercial entities, whereas the standards for new organic solar cells made out of materials such as conductive polymers are efforts of research groups.

"Our research is also an open invitation for discussion. We hope that cooperation among the international research community will increase in future," the team adds.

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