Ionic liquid optimized buried interface between spray-coated NiOX and perovskite for efficient solar cells

Spray-coated nickel oxide (NiOX) has great potential as hole transport layer for the fabrication of efficient, stable metal halide perovskite solar cells (PSCs). However, emerging evidences demonstrate that the inferior contact and the redox reaction at the NiOX|perovskite buried interface limit the performance of the devices. Herein, a series of ionic liquids were selected to modulate this interface as well as the perovskite film morphology. The results show that 1-butyl-3-methylimidazole tetrafluoroborate (BMIMBF4) exhibits a strong interfacial coupling effect between NiOX and perovskite, which facilitates the perovskite crystallization and charge transfer at the interface. As a result, the BMIMBF4 enables an efficiency improvement from 17.7% to 20.1% (aperture area: 0.16 cm2). More importantly, the non-encapsulated devices retain 90% of their initial performance after aging under ambient conditions for 700 h (ISOS-D-1).