Trade-off between the Performance and Stability of Perovskite Light-Emitting Diodes with Excess Halides.

Incorporation of excess bulky organoammonium halides as additives is an efficient way to enhance the performance of perovskite light-emitting diodes (PeLEDs). The excess organoammonium halides can decrease the grain size and minimize the trap density to enhance radiative recombination. In this work, we reveal that the halides in excess additives also play a critical role in the operation stability of PeLEDs. With an increasing excess halide ratio, perovskite films gradually change from being rich in halide vacancies (V) to being rich in halide interstitials (I), both of which can promote halide migration and reduce the operation stability. By using mixed 4-fluorophenylmethylammonium iodide and 4-fluorophenylmethylamine as additives, the excess halide ratio can be controlled and both V and I can be minimized. Therefore, the operation stability of methylammonium lead iodide-based PeLEDs is enhanced significantly from 40 to 520 min. This work emphasizes the importance of controlling excess halide concentrations in terms of device performance and operation stability.