Reducing Nonradiative Losses of Air-Processed Perovskite Films via Interface Modification for Bright and Efficient Light Emitting Diodes

Developing ambient-air fabrication strategy is desirable for lowering down the fabrication cost of perovskite light emitting diodes (LEDs) and further promoting their broad applications. However, ambient humidity usually leads to undesirable interface and perovskite film quality, causing severe nonradiative losses and unsatisfactory device performance. In this work, an effective strategy to solve this problem and remarkably enhance the performance of perovskite LEDs is reported. The study reveals that the humidity-induced aggregation of self-assembled monolayer (SAM) in humid air can be eliminated by introducing a poly[(9,9-bis(3′-((N,N-dimethyl)-N-ethylammonium)- propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] dibromide (PFNBr) as an interface modifier, which reduces the interfacial defects and improves the perovskite crystallinity. The interaction between PFNBr and perovskite can further passivate the defects and suppress trap-assisted nonradiative processes, which significantly enhances the photoluminescence efficiency of the ambient-processed perovskite films. Furthermore, the energy level alignment is optimized and the hole injection is improved, thus resulting in more efficient and balanced charge injection. As a result, the green perovskite LEDs achieve a high external quantum efficiency of 12.06% and luminance of 22121 cd m⁻², representing the record values for the perovskite LEDs processed under such ambient-air condition, in accompany with an improved device stability.