So far, most techniques for modifying perovskite solar cells (PSCs) focus on either the perovskite or electron transport layer (ETL). For the sake of comprehensively improving device performance, a dual‐functional method of simultaneously passivating trap defects in both the perovskite and ETL films is proposed that utilizes guidable transfer of Eu 3+ in SnO 2 to perovskite. Europium ions are distributed throughout the SnO 2 film during the formation process of SnO 2, and they can diffuse directionally through the SnO 2/perovskite interface into the perovskite, while most of the europium ions remain at the interface. Under the synergistic effect of distributed Eu 3+ in the SnO 2 and aggregated Eu 3+ at the interface, the electron mobilities of ETLs are evidently improved. Meanwhile, diffused Eu 3+ ions passivate the perovskite to reduce trap densities at the grain boundaries, which can dramatically elevate the open‐circuit voltage ( V oc) of PSCs. Finally, the mainly PSCs coated on SnO 2:Eu 3+ ETL achieve a power conversion efficiency of 20.14%. Moreover, an unsealed device degrades by only 13% after exposure to ambient atmosphere for 84 days.
A dual‐functional method of simultaneously passivating trap defects in both perovskite and electron transport layer (ETL) films is proposed. Europium ions distribute throughout SnO 2 film and diffuse into perovskite, while most of Eu 3+ remain at the interface. Under the synergistic effect of distributed Eu 3+, the electron mobility of ETL is improved and the trap density of perovskite is also reduced.