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

ABSTRACT Poly (3,4‐ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) is a widely used hole transport material in tin‐lead perovskite solar cells, yet its photoelectric properties require further enhancement. Herein, we develop a rational gradient doping strategy using DL‐carnitine hydrochloride (DL‐ChCl) to regulate PEDOT: PSS and improve its buried interface with the tin‐lead perovskite. The DL‐ChCl induces high p‐type doping in PEDOT: PSS, resulting in enhanced conductivity and an elevated work function for improved hole extraction via favorable energy level alignment. Simultaneously, the crystallization quality of the tin‐lead perovskite is also enhanced by hindering Sn 2+ 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.