ИСТИНА

Low operational stability of perovskite solar cells represents a bottleneck issue hampering the commercialization of this exciting photovoltaic technology. Among different approaches proposed to tackle this problem, a particular promising is the application of so-called passivation coatings for modification of perovskite films. Typically, these are very thin (sometimes even monomolecular layers) films of some reagents that are introduced atop the absorber films or at the grain boundaries to decrease the density of defects and improve photovoltaic performance and/or operational stability of perovskite solar cells. There are hundreds of various additives or passivation coatings tested directly in photovoltaic cells, whereas the information on their action mechanisms is very scarce and controversial. One of the reasons is that these passivation coatings were mostly screened towards improving the ambient stability of perovskite solar cells, which is probably not the best approach since efficient encapsulation should solve the extrinsic stability problem. Surprisingly, there are almost no studies on the effect of such passivation coatings on the intrinsic photochemical and thermal stability of perovskite films. Obviously, having no such fundamental information it is hardly possible to draw any reliable conclusions about action mechanisms of certain passivation coatings or processing additives. Herein, we performed a systematic study to fill the aforementioned gap in knowledge. In particular, we investigated the impact of a broad range of passivation reagents (>30 compounds) on the intrinsic photochemical and thermal stability of perovskite thin films under well-controlled anoxic conditions. The influence of such parameters as loading of passivation additives in the perovskite ink, processing of passivation coatings above the absorber films, and their thickness were studied. The obtained results allowed us to (1) identify the most promising passivation coatings, (2) elaborate the appropriate procedures for passivation of perovskite films, (3) establish correlations between the molecular structures of the additives and their stabilization effect induced in perovskite films and (4) draw some conclusions about the action mechanisms of the most promising passivation coatings. The performed studies featured a tremendous potential of rationally designed passivation coatings to be used for blocking main intrinsic degradation pathways in complex lead halides and boosting spectacularly the operational stability of perovskite solar cells.