Publication date: 15th May 2026
A major challenge for the practical application of perovskite solar cells (PSCs) is their limited operational stability. In n–i–p device architectures, all state-of-the-art PSCs with high power conversion efficiencies (PCEs) currently rely on the benchmark hole transport layer (HTL) Spiro-OMeTAD, which is conventionally doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 4-tert-butylpyridine (tBP). However, these dopants substantially compromise device stability. Furthermore, the complex in situ oxidation processes associated with conventional Spiro-OMeTAD doping obscure the underlying mechanisms, thereby hindering the rational design of stable, high-efficiency HTLs.
Here, we introduce a clean, post-oxidation-free doping strategy for Spiro-OMeTAD based on stable organic radicals as dopants and ionic salts as dopant modulators, termed ion-modulated (IM) radical doping. In this approach, the organic radicals directly generate hole polarons, resulting in an immediate enhancement of conductivity and work function, while the ionic salts further tune the work function by modulating the energetics of the hole polarons. Previously, PSCs employing IM radical-doped Spiro-OMeTAD achieved high PCEs with excellent stability, exhibiting T80 lifetimes of approximately 1200 h under 70 ± 5% relative humidity and 800 h at 70 ± 3 °C without encapsulation, effectively mitigating the trade-off between efficiency and stability. By further optimizing the dopant system, we demonstrate a significant enhancement in the thermal stability of the Spiro-OMeTAD layer, which remains stable at temperatures up to 85 °C. Moreover, the resulting HTL effectively suppresses Au migration into the perovskite layer, further contributing to improved device stability.
Thanks for the financial support provided by the EIC Pathfinder (SUPERLASER) and the Swedish Research Council (VR 2022-04474).
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