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

The combined effects of compact TiO2 (c‐TiO2) electron‐transport layer (ETL) are investigated without and with mesoscopic TiO2 (m‐TiO2) 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‐TiO2 without SAM to m‐TiO2 with SAM. This is attributed to the synergistic effect of the m‐TiO2/MHP nanocomposite at the interface and the enhanced adhesion afforded by the iodine‐terminated silane SAM. The combination of m‐TiO2 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 cm2 active areas, respectively. These PSCs also have exceptionally long operational‐stability lives: extrapolated T80 (duration at 80% initial PCE retained) is ≈18 000 and 10 000 h for 0.1 and 1 cm2 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. Incorporation of a self‐assembled monolayer at the interface in mesoscopic perovskite solar cells (PSCs) results in simultaneous enhancement of mechanical reliability, operational‐stability, and power‐conversion efficiency (PCE). Threefold increase in the interfacial toughness in a PSC with PCE of over 24% is responsible for T80 (duration at 80% initial PCE retained) of ≈18 000 h. Possible underlying mechanisms are elucidated.