Azide additive acting as a powerful locker for Li+ and TBP in spiro-OMeTAD toward highly efficient and stable perovskite solar cells

The dopants of bis(trifluoromethane) sulfonimide lithium (Li-TFSI) and 4-tert-butylpyridine (TBP) in spiro-OMeTAD are significantly important for achieving highly efficient perovskite solar cells (PSCs). However, the volatility of TBP and hygroscopicity of Li-TFSI would accelerate the degradation process of PSCs. Herein, we demonstrated that the use of 1,6-diazidohexane (N3) in spiro-OMeTAD can retard the evaporation of TBP and avoid aggregation/migration of lithium salt, leading to an enhanced conductivity/uniformity of spiro-OMeTAD layer. Additionally, N3 can minimize the TBP-PbI2 complex formation to improve the stability at perovskite/hole transport layer interface. As a result, we achieved a champion device with a power conversion efficiency (PCE) of 22.7% under AM 1.5G illumination. The unencapsulated devices can maintain good stability under illumination conditions. These findings provide a new strategy for the designs of extrinsic dopants in spiro-OMeTAD to further advance the stability of PSCs.