The lack of thermal stability of perovskite solar cells is hindering their progress towards adoption in the consumer market. In this paper we produced devices according to four well established recipes, and characterised their photovoltaic performance as they are heated within the operational range. Using in situ heating in the transmission electron microscope, we identified mechanisms for structural and chemical changes, such as iodine and lead migration, which appear to be correlated to the synthesis conditions. In particular, we determined a correlation between exposure of the perovskite layer to air during processing, and elemental diffusion during thermal treatment.

Figure:  STEM cross-sections of perovskite solar cells manufactured with different approaches (A –in vacuum, B – in glovebox, C – in air, D – single step in glovebox) as they are heated in situ at different temperatures. Degradation of the layers is observable, as well as the nucleation of particles from Pb and I migrating from the perovskite layer).