A Gradient‐Doped PEDOT: PSS via Multifunctional DL‐Carnitine Hydrochloride for Efficient Tin‐Lead Perovskite Solar Cells

oxidation, passivating interfacial defects, and preventing the formation of lead iodide. As a result, a champion power conversion efficiency of the inverted tin-lead perovskite solar cell is enhanced from 18.56% to 21.23% with the open-circuit voltage as high as 0.865 V. The stability of the optimized device without encapsulation is also improved, sustaining 90% of its initial efficiency after aging in a nitrogen atmosphere for 1200 h. This work provides an effective gradient doping strategy to engineer the buried interface between PEDOT: PSS and tin-lead perovskite, improving the photovoltaic performance of tin-lead perovskite solar cells.