Eliminating Residue-Induced Degradation: A Volatile Dopant Strategy for High Performance Perovskite Photovoltaics

The development of high-performance perovskite solar cells requires hole transport materials that simultaneously provide high conductivity and effective moisture barrier properties. Lithium bis(trifluoromethanesulfonyl)imide has been widely adopted as a standard dopant to enhance the conductivity of Spiro-OMeTAD in conventional n-i-p structured devices. However, residual lithium ions tend to migrate during operation, which adversely affects both device performance and long-term stability. In this study, we introduce ammonium bis(trifluoromethanesulfonyl)imide (AM-TFSI) as a volatile alternative dopant that leaves no cationic residues (termed "residue-free" in this work). During the doping process, this dopant mostly volatilizes with negligible ionic residues, thereby effectively avoiding the ion migration problems typically associated with conventional dopants. This approach not only significantly improves hole mobility but also prevents the introduction of extrinsic cations into the perovskite lattice, resulting in substantially enhanced device durability. Consequently, the optimized n-i-p perovskite solar cells incorporating this residue-free doped hole transport material achieve a power conversion efficiency of 25.53%, along with markedly improved operational stability. This work presents a simple yet effective residue-free doping strategy that concurrently addresses efficiency and stability challenges in perovskite photovoltaics.