  One of the main challenges for perovskite solar cells (PSC) is their
stability, due to environment-induced perovskite decomposition. The resulting
decomposition compounds are mobile and may, therefore, react with charge
carrier extraction layers or the contact metallization, in addition to
enhancing the recombination rate in the absorber layer. In this contribution,
the influence of different contact metallization layers, such as aluminum (Al),
silver (Ag), gold (Au) and nickel (Ni) on the storage stability of inverted
planar methylammonium lead iodide (MAPI)-based perovskite solar cells without
encapsulation has been investigated. For this study current-voltage (J-V) and
impedance measurements in combination with scanning electron microscope (SEM)
and Energy-dispersive X-ray spectroscopy (EDX) analysis were used to examine
and correlate structural device information with the development of PSC
electrical properties. While a strong perovskite decomposition and further
iodide diffusion to the contacts were detected for devices using Al, Ag or Au
as cathode electrodes, the microstructure of Ni cathodes inhibits such
decomposition process. This experiment has allowed for the realization of MAPI
based solar cells with Ni contacts, which exhibit no efficiency decrease below
as-fabricated values for up to one month of storage and select AM1.5 testing in
ambient atmosphere.
