Effects of Organic Cations on the Structure and Performance of Quasi-Two-Dimensional Perovskite-Based Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) perovskites are efficient luminescent materials due to their self-assembled quantum-well structure. We found that the organic cations have a significant effect on the structure and performance of quasi-2D perovskite-based light-emitting diodes (LEDs). Two classic organic cations, formamidinium (FA) and methylammonium (MA), were chosen for investigation. The MA-based quasi-2D perovskite has the largest band-gap n = 1 phase and a photoluminescence quantum yield (PLQY) as high as 85.3%, whereas this n = 1 phase is almost absent in the FA-based quasi-2D perovskite, which shows a moderate PLQY of 73.5%. However, the FA-based perovskite shows a much higher external quantum efficiency (15.4%) than the MA-based perovskite (0.93%) in LEDs. The lower electroluminescence efficiency of the MA-based perovskite could be ascribed to the poor hole injection. These results showed the importance of rational design of the quasi-2D perovskite for efficient LEDs.