Zwitterionic ionic liquid synergistically induces interfacial dipole formation and traps state passivation for...

Defects at the interface and grain boundaries of perovskite solar cells (PSCs) will result in severe non-radiative recombination and open-circuit voltage (Voc) loss. Herein, we reported a zwitterionic ionic liquid imidazolium tetrafluoroborate (IMBF₄) to passivate the defects at tin dioxide (SnO₂)/perovskite interface. The results showed that the electron-rich nitrogen atom contained IM⁺ could diffuse into the buried perovskite to exhibit a strong chemical passivation effect on the organic vacancy defect by interacting with uncoordinated Pb²⁺. The F^- in BF₄^- has a strong coordination effect with Pb²⁺in perovskite and Sn²⁺ in SnO₂ synchronously to fill the anion vacancy defect. Also, the BF₄^- anions could help to form an interface dipole layer to increase the charge transfer rate and reduce the work function. The IMBF₄ modified device could achieve an efficiency enhancement from 20.18% to 23.05% by vacuum flash-assisted solution-processed, with the increased Voc from 1.09 V to 1.15 V. The unencapsulated IMBF₄ modified device could maintain 93% of the initial efficiency after ageing for 2000 h under ambient conditions by the ISOS-D-1 stability-testing protocols. This work emphasizes the importance of multifunctional additives in passivating defects and improving interface contact for achieving efficient and stable perovskite solar cells.