Unlocking the Full Potential of Spiro-OMeTAD in Perovskite Solar Cells: Towards Synthetic Routes, Doping Mechanism, Degradation, and Stability

Abstract

Spiro-OMeTAD remains the benchmark hole-transport material (HTM) in n-i-p perovskite solar cells (PSCs), playing a key role in achieving record power conversion efficiencies. However, its broad application has been critically hindered by intrinsic instability—a weakness not inherent to the spirobifluorene core, but fundamentally tied to its conventional doping system. The widespread use of hygroscopic lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) and volatile 4-tert-butylpyridine (tBP) introduces serious degradation pathways, such as Li⁺ migration, pinhole formation, electrode corrosion, and redox-induced de-doping. Additionally, molecular replacements for spiro-OMeTAD that require no chemical doping are highly desirable. In this review, we summarize recent advances in Spiro-OMeTAD-based HTMs for PSCs, covering four main aspects: (1) synthetic routes, (2) doping mechanisms, (3) degradation processes, and (4) strategies for enhancing stability. Finally, we provide an outlook on future challenges and strategies for industrial adoption. The evolution of Spiro-OMeTAD and next-generation HTMs will rely on developing “all-in-one” multifunctional formulations that integrate doping, ion immobilization, and defect passivation. Combined with scalable green synthesis, rigorous real-world stability testing, and integration with stable perovskite compositions, these approaches can transform Spiro-OMeTAD from a stability concern into a versatile platform for continued innovation.