Dual Functions of Defect Passivation and Hole Transport Dopant Enabled by Piperidyl Ionic Liquid for Stable and Efficient Perovskite Solar Cells

Perovskite solar cells (PSCs) have recently attracted rapid interest for harvesting solar energy. However, the defects in perovskite absorber and vulnerability of charge-transporting layer lead to unsatisfying stability, which limits their practical applications. Herein, we demonstrate that the addition of a piperidyl ionic liquid, that is, 1-butyl-1-methylpiperidinium bis(trifluoromethyl sulfonyl)imide ([BMP](+)[TFSI](-)), can serve as a dual functional additive for passivating the intrinsic defects in perovskite and simultaneously improving the hydrophobicity of hole transport layer. Consequently, the power conversion efficiency for the optimal planar PSCs significantly increases from 21.07% to 23.34%. Impressively, the unencapsulated champion cells display promising stability with a reservation over 80% of the initial efficiency after exposure to moisture air (65% +/- 5% relative humidity) for 1600 h. This work provides a facile strategy toward enhancing the efficiency and stability of PSCs.