Degradation of perovskite solar cells (PSCs) is often the result of exposure to extrinsic environmental factors: humidity, oxygen, and thermal stress. However, intrinsic factors, notably ion migration, are also linked to stability issues, such as via lattice strain[1] or phase segregation[2,3]. Being intrinsic, these factors could limit stability and energy yield in commercial devices even if they manage to achieve excellent isolation from the atmosphere.

The most extreme conditions under which ion migration could trigger degradation is under day-night cycling, where swings in the PSC’s internal electric fields will trigger large shifts in the distribution of ionic defects in the perovskite absorber. This challenge is recognised by the proposed day-night cycling stability testing protocol presented in the consensus statement for perovskite solar cell stability testing[4].

In this context, our work assesses the extent of the stress placed on PSCs by day-night cycling, relative to more conventional maximum power point tracking. We consider the influence of the perovskite composition, notably the number of different A-site cations and X-site halides (Double and Triple). Simultaneous with the day-night cycling, we capture photoluminescence (PL) intensity images to determine the spatial homogeneity of the degradation triggered by the cycling effects, and thus whether the degradation mechanisms are intrinsic to the film or precipitated by initial regions of heterogeneity.

Our analysis focuses on an inverted ITO/PolyTPD/PFN-Br/Perovskite absorber/C60/BCP/Au structure, fabricated using an anti-solvent method. The perovskite composition was based on triple cation and triple halide. Moreover, to examine the effect of perovskite composition and film fabrication route, triple and double halide-based perovskite was further formulated with the anti-solvent and vacuum zig method.

References:

1.         Tsai, H. et al. Light-induced lattice expansion leads to high-efficiency perovskite solar cells. Science 360, 67–70 (2018).

2.         Duong, T. et al. Light and Electrically Induced Phase Segregation and Its Impact on the Stability of Quadruple Cation High Bandgap Perovskite Solar Cells. ACS Appl. Mater. Interfaces 9, 26859–26866 (2017).

3.         A. Jacobs, D. et al. Lateral ion migration accelerates degradation in halide perovskite devices. Energy Environ. Sci. 15, 5324–5339 (2022).

4.         Khenkin, M. V. et al. Consensus statement for stability assessment and reporting for perovskite photovoltaics based on ISOS procedures. Nat. Energy 5, 35–49 (2020).