Insulating‐Passivating Interfaces for Narrow‐Bandgap Tin‐Lead Perovskites Enable High‐Photovoltage in Single‐ and Double‐Junction Solar Cells

Reducing non‐radiative charge‐carrier recombination at both p‐ and n‐side interfaces of the perovskite layer is crucial for realizing high‐voltage single‐ and multi‐junction solar cells. Herein, it is demonstrated that co‐depositing a mixture of ethane‐1,2‐diammonium iodide and different oleyl‐based amphiphiles renders a passivator‐insulator modification at the perovskite–C 60 interface, which suppresses n‐side contact losses in narrow‐bandgap (∼1.26 eV) Sn–Pb perovskite solar cells. Interestingly, a cationic oleyl‐based amphiphile introduced concurrently with the poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate hole‐transport‐layer, deposited from an aqueous dispersion in 1‐propanol, also reduces the p‐side energy loss by providing a substrate for high‐quality perovskite films and limiting the contact between the doped hole‐transport‐layer and the perovskite layer atop. This double‐sided interface modification strategy enables open‐circuit voltage ( V oc ) values of up to 0.91 V—over 91% of the detailed‐balance limit—for 22.6% efficient single‐junction Sn–Pb perovskite solar cells. Monolithic all‐perovskite tandem solar cells show V oc and efficiency values of up to 2.16 V and 26.1%, respectively. The results demonstrate that insulating‐passivating interface modifications between the perovskite and charge transport layers represent an effective strategy for reducing energy losses in emerging perovskite solar cell technologies.