Abstract
Intensive development of organometal halide perovskite solar cells has lead to a dramatic surge in power conversion efficiency up to 20%. Unfortunately, the most efficient perovskite solar cells all contain lead (Pb), which is an unsettling flaw that leads to severe environmental concerns and is therefore a stumbling block envisioning their large-scale application. Aiming for the retention of favorable electro-optical properties, tin (Sn) has been considered the most likely substitute. Preliminary studies have however shown that Sn-based perovskites are highly unstable and, moreover, Sn is also enlisted as a harmful chemical, with similar concerns regarding environment and health. To bring more clarity into the appropriateness of both metals in perovskite solar cells, we provide a case study with systematic comparison regarding the environmental impact of Pb- and Sn-based perovskites, using zebrafish (Danio Rerio) as model organism. Uncovering an unexpected route of intoxication in the form of acidification, it is shown that Sn based perovskite may not be the ideal Pb surrogate.
Highlights
Within the branch of photovoltaic solar energy, crystalline silicon solar cells have been the prevailing technology for more than half a century
The general consensus is that mild humidity leads to a reversible hydrated perovskite-H2O complex[23,24,35], and upon complete disintegration of the perovskite crystal, PbI2 and CH3NH3I are formed, which can in part further degrade into CH3NH2, hydroiodic acid (HI), and I2, in parallel with Pb clusters being formed, but only to a lesser extent[14,16,36]
There are no published studies on the degradation of CH3NH3SnI3, but the focus of this work makes an elementary comparison between degraded Pb-based and Sn-based perovskites apposite using X-Ray Diffraction (XRD) as material-sensitive probe, it can be recognized in Fig. 1a that annealing of a pristine CH3NH3PbI3 film for 30 min. at 200 °C in air induces, as expected, the complete transformation of the perovskite into PbI214,16,36
Summary
Within the branch of photovoltaic solar energy, crystalline silicon solar cells have been the prevailing technology for more than half a century. Many proposed the replacement of Pb by tin (Sn) in order to render perovskite light absorbers less toxic or even nontoxic[19,25,26,27,28] Compared to their Pb-based counterparts, Sn-based perovskites so far show inferior device performance, and they are even more www.nature.com/scientificreports/. One important scenario to be addressed could be a structural failure of a solar panel, resulting in (i) the full degradation of its perovskite absorber material when being exposed to ambient, followed by (ii) the dissolution of the decomposition products in water on a rainy day later on. As a first step, the main degradation products of Pb and Sn-based perovskites need to be established before proceeding to their toxicological assessment in an aqueous environment by means of the model organism zebrafish Danio rerio, employing the Zebrafish embryo acute toxicity testing (ZFET) protocol. The results from our study lead to a first nuanced comparison of the environmental impact of degraded Pb and Sn-based perovskites
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