Restricting Li ⁺ Migration via Mixed Hole Transporting Materials Strategy for Stable tBP‐Free Perovskite Solar Cells

ABSTRACT Lithium bis(trifluoromethanesulfonyl)imide (Li‐TFSI) and 4‐tert‐butylpyridine (tBP) are critical dopants in hole transporting materials (HTMs) for achieving highly efficient n–i–p perovskite solar cells (PSCs). However, the migration of Li ⁺ and the volatility of tBP seriously affect the long‐term stability of PSCs. In this work, a facile strategy is proposed by mixing a developed terpyridine‐based HTM (TPy‐CzDPA, simultaneously serving as a tBP alternative) and Li‐TFSI into spiro‐OMeTAD. Owing to the multidentate structure and strong electrostatic potential of the terpyridine unit, TPy‐CzDPA forms a stable coordination with Li ⁺ , which effectively restricts the migration of Li ⁺ and inhibits the associated hydrolysis. Furthermore, replacing tBP with TPy‐CzDPA confers not only enhanced thermal stability but also a higher hole mobility of 2.53 × 10 ⁻⁴ cm ² v ⁻¹ s ⁻¹ to the mixed HTMs. Consequently, the PSCs based on mixed HTMs achieve a champion power conversion efficiency (PCE) of 22.13% along with preferable stability. The PSCs with PTAA‐based mixed HTMs retain 90% of initial efficiency after 528 h storage at 80°C, while the encapsulated devices exhibit only a 14% drop in PCE after 4800 h storage under 30–40% relative humidity (RH). This work provides a new strategy to promote the performance of tBP‐free PSCs.