Enhancing the photo-luminescence stability of CH₃NH₃PbI₃film with ionic liquids

The methylammonium lead triiodide (CH3NH3PbI3)-based perovskite shows a great alluring prospect in areas of solar cells, lasers, photodetectors, and light emitting diodes owing to their excellent optical and electrical advantages. However, it is very sensitive to the surrounding oxygen and moisture, which limits its development seriously. It is urgent to spare no effort to enhance its optical and electrical stability for further application. In this paper, we synthesize the MAPbI3 perovskite film on the glass substrate with/without the ionic liquid (IL) of 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) by a simple two-step sequential solution method. The additive of BMIMBF4 can improve the quality of crystal structure. Moreover, the photo-luminescence (PL) intensity of MAPbI3 film with BMIMBF4 is much stronger than the pure MAPbI3 film after a week in the air, which is almost ten-fold of the pure one. Meanwhile, under the illumination of 405-nm continuous wave (CW) laser, the fluorescent duration of the MAPbI3 film with BMIMBF4 is approximately 2.75 min, while the pure MAPbI3 film is only about 6 s. In fact, ionic liquid of BMIMBF4 in the perovskite film plays a role of passivation, which prevents the dissolution of MAPbI3 into CH3NH3 and PbI2 and thus enhances the stability of environment. In addition, the ionic liquid of BMIMBF4 possesses high ionic conductivity, which accelerates the electron transport, so it is beneficial for the perovskite film in the areas of solar cells, photodetectors, and lasers. This interesting experiment provides a promising way to develop the perovskite's further application.