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

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 Sn²⁺ 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.