Triple-junction all-perovskite solar cells with self-assembling hole contacts in all subcells

Despite rapid advances in all-perovskite multi-junction devices, the prevalent hole-transport layer (HTL), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), constrains stability and efficiency in narrow-band-gap tin-lead (Sn-Pb) bottom cells due to acidity and parasitic absorption. Although self-assembled monolayers (SAMs) are well established as HTLs in Pb perovskites and therefore considered promising for Sn-Pb perovskites, their implementation is lagging behind. In this study, we uncover the underlying mechanism by which SAMs limit charge extraction and induce non-uniform buried interfaces in Sn-Pb perovskite films. Guided by these insights, we demonstrate that a graphene oxide/SAM bilayer concurrently mitigates electronic and ionic losses, enabling 22.1% single-junction Sn-Pb efficiency with a 0.88 V open-circuit voltage. In all-perovskite triple-junctions, the bilayer reduces parasitic absorption losses in the near-infrared, yielding 27.3% efficiency (stabilized at 27.0%). The bilayer's chemically benign nature improved device stability, retaining 90% of initial efficiency after 770 h of operation at 25°C.