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Organic−inorganic hybrid perovskite solar cells (PSCs) have emerged as a promising candidate for next-generation solar cells. However, the limited stability of PSCs hampers their practical applications. In this work, for the first time, a functionalized π-conjugated ionic liquid crystal (ILC), 4′-(N,N,N-trimethyl ammonium bromide hexyloxy)-4-cyanobiphenyl (6CNBP-N), is developed as a novel chemical additive to obtain CH 3 NH 3 PbI 3 (MAPbI 3 ) PSCs with high efficiency and excellent moisture stability. This 6CNBP-N ILC possesses the characteristics of ionic liquids and liquid crystals. The inclusion of the 6CNBP-N ILC can effectively improve the quality and stability of perovskite films, reduce the trap-state densities, and promote the carrier transport induced by the cyano group (CN), a rod-like π-conjugated biphenyl mesogenic unit and quaternary alkylammonium cations (R 4 N + ) in 6CNBP-N. Through this functionalized ILC engineering strategy, the power conversion efficiency (PCE) of PSCs is greatly increased from 18.07% for the control PSC to 20.45% for the PSC with 6CNBP-N along with the depressed hysteresis effect and enhanced moisture stability of PSCs. Our work provides a new strategy for designing functionalized additives for highperformance PSCs.

In this work, a novel back contact interface engineering is developed for inverted planar perovskite solar cells, in which a tetrafluoroterephthalic acid (TFTPA) interlayer is inserted between CH 3 NH 3 PbI 3 and PC 61 BM to strengthen the interface contact. Benefiting from the strong Coulombic interactions between positive electron-poor tetrafluoroterephthalate moieties and negative electron-rich fullerene molecules, as well as the coordinate effect between −COOH groups of TFTPA and Pb 2+ ions of perovskites surface, a tightly jointing and defectpassivated CH 3 NH 3 PbI 3 /PC 61 BM interface is formed. The strengthened CH 3 NH 3 PbI 3 /PC 61 BM back contact can significantly facilitate electron transport and simultaneously diminish the charge accumulation and recombination. Therefore, power conversion efficiency (PCE) of the TFTPA device is up to 19.39%, whereas the hysteresis effect is weak, and the PCE is improved by 20.4% compared with the control device which does not have a TFTPA interlayer. Particularly, the moisture stability of the TFTPA device is greatly improved as compared to the control device. Our findings illustrate that the back contact interface engineering is an important and promising approach for inverted planar perovskite solar cells.

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