A group of researchers led by Helmholtz-Zentrum Berlin (HZB) in Germany and China’s Henan University investigated repeated thermal stress cycles, reflecting diurnal cycles, on the degradation of metal halide perovskite solar cells.
Its results and proposed solutions appear in a perspective paper, “Resilience Pathways for Halide Perovskite Photovoltaics Under Temperature Cycling,” published by Nature Reviews Materials.
By subjecting perovskite solar cells to repeated temperature changes – the cells were cooled to minus 150 C and then heated to plus 150 C, the team was able to study the changes in the microstructure of the perovskite layer and its interactions with the layers of the cell stack. The group noted divergent thermal behaviors of the various materials. Furthermore, local phase transitions and diffusion of elements into adjacent layers were observed.
It concluded that thermal stress is the “decisive factor” in the degradation of metal-halide perovskites. While encapsulation can effectively protect the cells from moisture and atmospheric oxygen, it pointed out, the devices are still exposed to daily temperature variations throughout the year. In the desert, for example, temperatures inside the solar cells can range from minus 40 C to plus 100 C.
To make the perovskite and adjacent layers more resilient to thermal stress, the researchers suggested “enhancing material crystallinity” or using buffer layers to relieve “interlayer thermal stress.”
They also stressed the importance of uniform testing to facilitate comparison between different studies, as a prelude to its proposal of a unified approach for evaluating stability under temperature cycling.
The researchers from the aforementioned institutions were joined by scientist collaborators from the University of Oxford, Università degli Studi di Cagliari, Henan Normal University, Swiss Federal Institute of Technology (EPFL), Southeast University, University of Stuttgart, Universidad de Valencia, IEK5-Photovoltaics Forschungszentrum Jülich, Bielefeld University, and University of the Basque Country UPV/EHU.
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