Ryma Iness Benmessaoud
Solar radiation currently represents the most important source of renewable energy. Existing technologies to collect and distribute solar energy are expensive, difficult to manufacture, non-recyclable and not very cost-effective. Recent advances in physics and materials engineering have pointed to photovoltaic (PV) perovskites (or CH3NH3MI3, where M=Pb, Sn) as the future solution for sustainable energy because of their simple fabrication procedure, low price, and high efficiency. Several companies are already building perovskites-based PV devices for commercialization in the near future. Nevertheless, perovskites contain heavy metals, and safety concerns during PV fabrication and transportation have not yet been addressed, not to mention recycling, and environmental hazards in case of any failure of large-area solar panels. This dissertation documents my investigation of the potential health and environmental effects of perovskites. I have performed a "zoom-in approach" on human cells to study gene expression and biochemical changes, and a "zoom-out approach" in vivo to investigate toxicity at an organism level. The time frame during which living cells can be manipulated on the same substrate is short, therefore we selected concentrations in the range of 50 to 200 µg /ml (from 80 to 400 µM)) to observe a measurable effect in vitro. These concentrations may seem relatively high, however, an accidental exposure scenario with such concentrations may occur during material fabrication if safety measures are not taken properly. In the in vitro study using human cells, I have discovered not only a dose- and time-dependent response to perovskites exposure, but also a cell-type dependent effect. Within 24 hours following perovskites exposure, neuronal cells died whereas lung cells became giant and polynucleated. Complementary assays showed that mitochondria were heavily damaged, with an increase in their activity when compared to untreated cells. Furthermore, genome profile studies showed many differences in gene expression levels. Extra analysis identified the co-regulated gene networks rather than individual coding genes, which indicated that some pathways critical to basic cellular functions were heavily affected by perovskite exposure (such as regulation of the metabolism, cell division, cell signaling etc.). To understand more thoroughly, I applied the Scanning Fourier Transform Infrared Microspecrometry (S-FTIRM) to study cell toxicity. This has never been done before. I investigated the biochemical changes displayed on infrared absorption spectra. The results are complementary to other techniques, which makes the use of S-FTIRMS applicable to real-time toxicity studies because of its submolecular sensitivity and high-resolution. I also explored the eco-toxic effects of photovoltaic perovskites on small model organisms: fruit flies (Drosophila melanogaster) and nematodes (Caenorhabditis elegans). In both models, life span and organism development were reduced by the exposure. Moreover, the fertility of young adults was drastically affected. My in vitro and in vivo studies showed that CH3NH3PbI3 and CH3NH3SnI3 are acutely and chronically toxic compounds. The obtained results are conclusive, and encourage the scientific community not only to conduct further tests on more complex organisms, but to first search for novel solutions with non-toxic properties.
EPFL2017
