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Wednesday, 22 January 2020

A consensus statement establishes the protocols to assess and report stability of perovskite photovoltaic devices

The existing characterization procedures to evaluate emerging photovoltaic devices are not appropriate for halide perovskite solar cells, a new generation of solar cells called to overcome the present state-of-the-art technologies. A vast group of scientists, led by Prof. Mónica Lira-Cantú (ICN2) and Prof. Eugene A. Katz (Ben-Gurion University of the Negev), have reached a consensus on the suitable procedures and the variables to be reported in stability studies of this kind of solar cells. The consensus statement, highlighted in the last issue of Nature Energy, updates the ISOS protocols for the stability assessment of perovskite photovoltaics with additional procedures to account for properties specific to this technology.

Perovskite solar cells (PSCs) are a new kind of photovoltaic devices expected to rival the widespread silicon ones. Efficiency of perovskite-based solar cells is already superior, but their lifespan must be extended. This is the pending issue for the PSCs to reach commercialization. However, the existing qualification tests to evaluate the performance of solar cells are not appropriate for PSCs, as these have different material properties and device architectures. Therefore, publications studying the stability of PSCs lack consistency in the experimental procedures used and the parameters reported, which hampers data comparison and a proper understanding of the cell degradation mechanisms.

A large group of scientists decided to put an end to this situation: 59 leading researchers from 51 affiliations have agreed on the ways in which the stability of perovskite cells should be assessed and reported. The discussion was led by Prof. Mónica Lira-Cantú, Group Leader of the ICN2 Nanostructured Materials for Photovoltaic Energy Group, and by Prof. Eugene A. Katz, Professor at the Ben-Gurion University of the Negev, Israel. Among the authors are remarkable researchers such as Prof. Nam-Gyu Park and Prof. Henry J. Snaith, Nobel Prize candidates in 2017 for their discovery of the perovskite cells. The result of the discussion is a consensus statement published today in Nature Energy and highlighted in the journal editorial.

Inspired by their colleagues working on organic photovoltaic cells, who in 2011 developed recommendations for evaluating the stability of their devices (so-called ISOS protocols), the scientific community devoted to PSCs started their own debate. Gathered in the 11th International Summit on Organic and Hybrid Photovoltaics Stability held in China in October 2018, a round table discussing PSCs stability assessment was at the origin of the present work.

The experts have complemented the existing protocols with a set of testing procedures that account for specific features of PSCs, including light-dark cycling, the study of cell behaviour under electrical bias in the dark or intrinsic stability testing, among others. The researchers have also proposed a checklist for reporting results aimed at improving reproducibility.

These new protocols are the final outcome of the COST Action Stable NextSol MP1307, led by Prof. Mónica Lira-Cantú, which involved more than 480 participants from 35 countries and 22 industries aimed at studying the stability of organic and perovskite solar cells. However, there is still work to be done. A technical report is the next step to pave the way for standardization, which would be the last station in this journey from lab to industry. In the context of a society demanding green solutions for energy production, the efforts devoted to standardise the study of perovskites facilitate the advance towards a new generation of enhanced solar cells.

Article reference:
Mark V. Khenkin, Eugene A. Katz, et. al., Mónica Lira-Cantú. Consensus Statement for Stability Assessment and Reporting for Perovskite Photovoltaics based on ISOS Procedures. Nature Energy 5, 35–49 (2020).
http://dx.doi.org/10.1038/s41560-019-0529-5