The hole transport layer (HTL) is a major component in PSCs that ensures photogenerated holes are effectively extracted. With respect to n-i-p PSCs, when lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) and tert-butylpyridine (tBP) are employed as dopants, conventional 2,2′,7,7′-tetrakis (N, N-di-p-methoxyphenyl-amine) 9,9′-spirobifluorene (spiro-OMeTAD) is one of the most commonly used HTL materials, where it plays a significant role in fabricating high-performance devices. [1][2][3] LiTFSI is a redox inactive agent that participates in the oxidation reaction through lithium-ion consumption. This accelerates the p-doping of spiro-OMeTAD by oxygen to increase conductivity and hole mobility. [2,4,5] In addition, tBP helps promote the dispersion of Li-TFSI in HTL solution and enhances the wettability of perovskite films to improve the HTL morphology. [1,[6][7][8] However, LiTFSI has been shown to be a hygroscopic salt with a tendency to absorb moisture from air and aggregate in spiro-OMeTAD. This causes moisture-induced degradation of both the HTL and underlying perovskites. [9,10] In addition, the interaction of LiTFSI and tBP generates numerous pinholes in HTL, which accelerates the degradation of PSCs. [11,12] Finally, the top electrode of silver is unfavorable because the I − ions penetrate the spiro-OMeTAD layer through pinholes. This induces the formation of AgI, which results in critical nonradiative recombination. [13,14] On the other hand, high-performance devices often require another buffer layer between the perovskite and the conventional spiro-OMeTAD films to passivate surface defects of the perovskite layer, which increase the complexity of the device fabricating process. [15][16][17][18][19][20] Therefore, many studies have addressed spiro-OMeTAD stability and the aforementioned perovskite surface issues. In 2014, Nguyen et al. synthesized spiro-OMeTAD(TFSI) 2 by combining spiro-OMeTAD with AgTFSI, where spiro-OMeTAD + was obtained by the reaction of spiro-OMeTAD 2+ and spiro-OMeTAD. This method realized the oxidization of spiro-OMeTAD without relying on oxidation in air, thereby increasing the stability of the device. [21] In addition, compounds with TFSI − have also been proven to be a class of effective p-type dopants that can increase the stability of spiro-OMeTAD because of the Perovskite solar cells (PSCs) with n-i-p structures often utilize an organic 2,2′,7,7′-tetrakis (N, N-di-p-methoxyphenyl-amine) 9,9′-spirobifluorene (spiro-OMeTAD) along with additives of lithium bis(trifluoromethanesulfonyl) imide salt (LiTFSI) and tert-butylpyridine as the hole transporting layer (HTL). However, the HTL lacks stability in ambient air, and numerous defects are often present on the perovskite surface, which is not conducive to a stable and efficient PSC. Therefore, constructive strategies that simultaneously stabilize spiro-OMeTAD and passivate the perovskite surface are required. In this work, it is demonstrated that a novel ionic liquid of dimethylammonium bis( trifluoromethanesulfonyl)imide (DM...
