Simultaneous Enhancement of Efficiency and Operational‐Stability of Mesoscopic Perovskite Solar Cells via Interfacial Toughening

Abstract The combined effects of compact TiO 2 (c‐TiO 2 ) electron‐transport layer (ETL) are investigated without and with mesoscopic TiO 2 (m‐TiO 2 ) on top, and without and with an iodine‐terminated silane self‐assembled monolayer (SAM), on the mechanical behavior, opto–electronic properties, photovoltaic (PV) performance, and operational‐stability of solar cells based on metal‐halide perovskites (MHPs). The interfacial toughness increases almost threefold in going from c‐TiO 2 without SAM to m‐TiO 2 with SAM. This is attributed to the synergistic effect of the m‐TiO 2 /MHP nanocomposite at the interface and the enhanced adhesion afforded by the iodine‐terminated silane SAM. The combination of m‐TiO 2 and SAM also offers a significant beneficial effect on the photocarriers extraction at the ETL/MHP interface, resulting in perovskite solar cells (PSCs) with power‐conversion efficiency (PCE) of over 24% and 20% for 0.1 and 1 cm 2 active areas, respectively. These PSCs also have exceptionally long operational‐stability lives: extrapolated T 80 (duration at 80% initial PCE retained) is ≈18 000 and 10 000 h for 0.1 and 1 cm 2 active areas, respectively. Postmortem characterization and analyses of the operational‐stability‐tested PSCs are performed to elucidate the possible mechanisms responsible for the long operational‐stability.