“…polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), which registered low PCEs [5,13,73,76,108]. Moreover, the need for improved stability, cost-effectiveness and efficiency, have directed researchers to rethink the architecture and formulation of perovskite devices, by application of various organic composites and co-polymers, such as PCBM (phenyl-C61-butyric acid methyl ester), P3HT (poly(3-hexylthiophene) and PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrenesulfonate) [109,110], different carbon allotropes (carbon nanotubes, graphene and fullerene) [109,111,112], and alternative metal oxides (Al 2 O 3 , ZnO, SnO 2 , NiO x ) [113][114][115][116][117][118]. Figure 2a displays the typical structure of direct stacked (n-i-p) architecture of a standard thin film perovskite solar cell and the arrangement of molecules in a single perovskite unit.…”