  Highly-efficient solar cells containing lead halide perovskites are expected
to revolutionize sustainable energy production in the coming years. Combining
these next-generation solar panels with agriculture, can optimize land-use, but
brings new risks in case of leakage into the soil. Perovskites are generally
assumed to be toxic because of the lead (Pb), but experimental evidence to
support this prediction is scarce. We used Arabidopsis thaliana to test the
toxicity of the lead-based perovskite MAPbI3 (MA = CH3NH3) and several of its
precursors in plants. Our results show that MAPbI3 severely hampers plant
growth at concentrations above 5 microM. Surprisingly, we find that the
precursors MAI is equally toxic, while lead-based precursors without iodide are
only toxic above 500 microM. These observations reveal that perovskite toxicity
at low concentrations is caused by iodide ions specifically, and contrast the
widespread idea that lead is the most harmful component. We calculate that
iodide toxicity thresholds are likely to reach in the soil upon perovskite
leakage, but much less so for lead toxicity thresholds. Hence, this work
stresses the importance to further understand and predict harmful effects of
iodide-containing perovskites in the environment.
