Soil tests raise health concerns about perovskite
Results suggest current risk assumptions are too low.
By Barry Keily
Experiments using plants have raised new concerns about the environmental impact of perovskite solar cells (PSCs), a key component for the commercialisation of the next generation of large- and small-scale renewable energy technology.
Perovskite is a mineral containing calcium titanium oxide. It is combined with a hybrid organic-inorganic lead or tin halide light-collecting layer to produce solar cells that are comparatively cheap and easy to manufacture.
Depending on the design, they can reach conversion efficiencies as high as 28%, putting them well in front of other solar cell technologies and making them the focus of huge amounts of investment as corporations push towards full commercialisation.
Lead-based PSCs are the most commonly manufactured, and thus far the amount of lead contained within them – less than 0.1% by weight – has caused little concern because it is well below the safety limit imposed by most countries.
New research conducted by a team led by Antonio Abate of the Helmholtz-Zentrum Berlin für Materialien und Energie in Germany, however, raises fresh concerns about the environmental – and by extension, human – costs of the cells.
Abate and colleagues from Italy and China grew a selection of common food plants, including mint, chilli and cabbage, in soil that contained lead-based PSCs. In an unexpected result, all the plants absorbed the trace levels of lead in the growing medium much more readily than predicted.
Indeed, the researchers found that the lead in PSCs was 10 times more bioavailable than it was from any other likely contaminant source, increasing the likelihood that it could find its way into the human food web.
Writing in the journal Nature, the researchers say that the finding must change the assumptions that underlie PSC risk assessments.
“We highlight that the environmental impact of lead perovskite cannot be estimated on a linear scale of effect versus concentration, as it was tacitly assumed up to now,” they conclude.
In a second stage of the research, Abate and colleagues repeated the experiment in soil containing tin halide PSCs and found that uptake by the plants well below established risk levels.
The results, they conclude, demonstrate the need for broader and more systematic screening of perovskite products as the technology surges towards market dominance.