The news story in the Oxford Photovoltaics post is misleading, especially the caption describing the materials as "non-toxic". This is wrong; the cells are made with lead as well as the organic components. Lead-free perovskite solar isn't good yet. Of course, Oxford PV goes very far out of their way to downplay the lead content of their products; on their page they refer to lead iodide only as "yellow precursor salt" to confuse the public. Wikipedia has some useful info on perovskite solar.
I’ll admit that I was unaware of the fact that perovskike solar cells typically contain lead – 5 seconds on Google shows this to be true. However, Oxford Photovoltaics put out a press release in 2014 on lead-free perovskites, so they’ve clearly been working on this for some time.
“This is a hugely important breakthrough which could have a significant impact on the speed with which we can bring this important technology to market […] the elimination of lead will certainly reduce customer concerns over recyclability over the life of the product.”
– Kevin Arthur, Chief Executive
Still, I was curious. So I did some digging…
Oxford Photovoltaics apparently base their technology on the work of Henry Snaith, a professor at the University of Oxford. A quick check of his recent publications finds that he has indeed worked on lead halide perovskites. Unsurprisingly, given their prevalence in the field.
Though Snaith has also done a lot of work on substituting metals in the perovskite compounds (Klug et al, 2016), as well as on lead-free perovskites (Volonakis et al, 2016). Of particular interest, Sakai et al (2017) report a study on Cesium Bromopalladate (Cs₂PdBr₆), a non-toxic alternative. Given this compound is solution processable, which links with the fact that Oxford Photovoltaics’ solar glass is described as “printed”, I suspect this may be the compound which they’re employing.
Additionally, as I’m guessing you probably know, lead halide perovskites are killed pretty easily by water, so a window pane made from them wouldn’t last long – especially somewhere as damp as the UK! Cesium bromopalladate reportedly fixes this, as the compound is water resistant.
In my experience, what gets published by any given lab is typically a few years behind their current capability, especially where industry contracts are involved (proprietary periods can last a long time). The headline in my post was sourced from the Guardian (actually 4 years ago) and, quite frankly, making a false claim that something is non-toxic when it isn’t in front of an international audience like that would be tantamount to career suicide, as well as setting the whole industry back years. This all leads me to the logical conclusion that they aren’t using lead in their products.
Admittedly though, confirmation would need to come from Oxford Photovoltaics themselves. Perhaps I should send them an e-mail to ask…
Incidentally, while looking I found another article by Hoye et al (2017), on bismuth oxyiodide as a replacement for lead, which you might find interesting. Apparently, these bismuth-based photovoltaics are even more efficient than lead based ones.
That all turned into quite a rabbit hole, but it was very informative, so thanks for your comment!
Ps: Putting the fun in density functional theory? Nice. 😉
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