Strategies of how to mitigate photodegradation and thermal degradation processes are proposed in this work in order to further improve operational stability in hybrid perovskite solar cells.
Nanocrystals of MgO and CaO have been prepared by a modified aerogel/hypercritical drying/dehydration method. For nanocrystalline MgO (AP-MgO) surface areas ranged from 250 to 500 m 2 /g, whereas for AP-CaO 100-160 m 2 /g. These materials have been compared with more conventional (CP) microcrystalline samples of lower surface area with regard to (1) morphology (AP-samples (autoclave preparation) are tiny polyhedral crystallites, while CP-samples (conventional preparation) are larger, hexagonal platelets and cubes);(2) residual surface OH (AP-samples have less acidic OH, which are more isolated from each other; (3) acid gas adsorption (AP-samples adsorb more SO 2 and CO 2 at low pressures and room temperature and prefer monodentate rather than bidentate adsorption modes, but at higher pressures CP-samples adsorb more SO 2 and HCl apparently due to the formation of more well ordered multilayers); (4) destructive adsorption of organophosphorus compounds and chlorocarbons (AP-samples are superior due to higher surface areas and higher surface reactivities), and (5) very thin layers of transition metal oxides on the MgO and CaO nanocrystals that significantly enhance destructive adsorption capacities to the point where [M x O y ]AP-MgO and [M x O y ]-AP-CaO become stoichiometric in reaction with CCl 4 . The data are conclusive that the nanocrystals are more reactive than the microcrystals, and this is mainly attributed to morphological differences, including defects. However, intrinsic electronic effects due purely to "smallness" cannot be ruled out.
Nowadays the major factors determining commercialization of lead halide perovskite photovoltaic technology are shifting from solar cell performance to stability, reproducibility, up-scaling, and in particular the concern of Pb leakage during solar cell operation. Here we simulate a realistic scenario that the perovskite solar modules with different encapsulation methods are damaged to a typical extent by mechanical impact (according to the modified FM 44787 standard) and quantitatively measure the lead leakage rates from the damaged modules. We demonstrate that an epoxy resin (ER) based encapsulation method reduces the Pb leakage rate by a factor of 375 compared to the encapsulation method using a glass cover with the UV-resin cured at the module edges. The excellent Pb leakage prevention characteristics is due to the self-healing property of ER and increased mechanical strength. These findings strongly suggest lead halide perovskite photovoltaic products can be used with minimal Pb leakage if appropriate encapsulation is employed.
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