As a green solvent, ionic liquids (ILs) are considered as a promising alternative to conventional polar aprotic solvents for the production of efficient and stable perovskite solar cells (PSCs). Moreover, with the use of IL solvents, perovskite films can be prepared without antisolvent treatments in an ambient environment instead of in a glovebox with inert gases, which simplifies the film manufacturing process and is favorable for industrialization production. However, the type of IL solvents that have been studied is limited, and the influence of IL molecular structures on the perovskitefilm crystallization and device performance is not completely understood. In this work, four different ILs, methylammonium formate (MAF), methylammonium acetate (MAAc), methylammonium propionate (MAP), and mthylammonium isobutyrate (MAIB), are synthesized as the perovskite precursor solvents. The interaction between the functional groups of the synthesized solvents and Pb 2+ in the precursor solution is studied, which has a direct impact on the morphology and crystallization of the deposited perovskite film. It is found that MAP solvent gives a high-quality perovskite film, which leads to the best photovoltaic performance with a champion PCE of 20.56% compared to the devices based on the other IL solvents. Moreover, the MAP-based device maintains 88% of its original PCE after 1000 h of storage in a N 2 atmosphere, demonstrating excellent device stability. Therefore, it is concluded that MAP is the most suitable solvent for MAPbI 3 films with respect to photovoltaic applications as compared to the other ILs.

In recent years, organic−inorganic hybrid perovskite solar cells (PSCs) have attracted extensive attention due to their high power conversion efficiency (PCE) and simple preparation process. The selection and optimization of the hole transport layer (HTL) are very important for device performance. Compared to other HTLs, nickel oxide (NiO x ) has been widely used in PSCs due to its good chemical stability, high hole mobility, and simple preparation method. This review begins with the application of NiO x HTL in planar PSCs and systematically introduces the influence of the structure and photoelectrical properties of devices by doping and surface modification. The effects of NiO x modification on the power conversion efficiency (PCE), filling factor (FF), open-circuit voltage (V oc ), short-circuit current (J sc ), and stability of PSCs are reviewed in detail from the perspectives of energy-level matching, hole mobility, and crystallinity. Finally, the future of NiO x -based planar PSCs is discussed.

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Perovskite solar cells (PSCs) have gained much attention because of their expressive power conversion efficiency (PCE) of up to 25.5%. A good contact and a well-aligned energy level at the buried interfaces between electron transport layers (ETLs) and perovskite films play an essential role in promoting charge-carrier collection and suppressing nonradiative recombination. Currently, low-temperature-processed SnO2 thin films are widely used as the ETLs to achieve efficient and stable planar PSCs. However, fabricating proper SnO2/perovskite interfaces with a good contact and a well-aligned energy level is necessary but implies a great challenge. Herein, we modify the SnO2 ETL using benzylamine hydrochloride (BH), which is expected to facilitate the energy level alignment and to enhance perovskite crystallization. Moreover, the BH interlayer is found to effectively reduce the trap-state density and thereby improve the charge-carrier extraction between the ETL and the perovskite layer. Consequently, the PSC with BH modification yields a higher PCE, a lower hysteresis, and better stability than the device without a BH interlayer. This study highlights the key role of molecule modification of ETLs in designing efficient and stable PSCs.