Phase Distribution Manipulation through Molecular Interaction Enables Efficient Quasi-2D Perovskite Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) metal halide perovskites exhibit excellent electroluminescence (EL) performance promising for display and lighting applications, which benefits from the quantum and/or dielectric confinement effects as well as the unique energy-funneling process. However, the inefficient energy transfer caused by the intricate phase distribution with different thick nanoplatelets (n-values), as well as the existence of numerous defects, could deteriorate the EL performance of the resulting perovskite light-emitting diodes (PeLEDs). Here, a multifunctional small molecule, bistrifluoromethanesulfonimide lithium (LiTFSI), was introduced to address the above issues. The strongly electronegative fluorine atoms in LiTFSI form hydrogen bonding interactions with the ammonium heads of organic spacers, which suppress the formation of perovskite ultrathin nanoplatelet phases with small n-values, thus smoothing the energy transfer process. Meanwhile, the Lewis base sulfur oxide groups are capable of effectively passivating the uncoordinated lead ion defects and then reducing nonradiative recombination loss. Eventually, a green emission quasi-2D PeLED with an external quantum efficiency of 21.0% was achieved. This work provides a facile method to boost the performance of quasi-2D PeLEDs.