Interstitial Alkali Metal Ions Regulating the Phase Distributions Enabling Efficient and Stable Red Perovskite Light-Emitting Diodes

Quasi-2D perovskites have attracted intensive attentions for applications in light-emitting diodes (LEDs) due to their high exciton binding energy and good photostability. However, the wide phase distribution and inefficient energy transfer in quasi-2D perovskite are impeding the realization of efficient and stable pure red PeLEDs. Herein, an alkali metal iodide, potassium iodide (KI) is employed to in situ regulate the growth kinetics of quasi-2D perovskite film with three spacer cations of butylammonium (BA ⁺ ), 2-phenylethanamine (PEA ⁺ ), 2-naphthylmethylammonium (NMA ⁺ ) by diffusing into the interstitial sites of octahedral structures. The KI treatment can not only facilitate the radiative recombination efficiency by controlling the phase distributions of low-n and high-n phases to improve the exciton energy transfer, but also passivate the Pb dangling bonds and compensate iodine vacancies (V _I ) effectively, which leading to the formation of smooth and dense film morphology. Based on the KI-treatment perovskite film, an efficient and color-stable pure-red PeLED with a peak external quantum efficiency (EQE) of over 10% was achieved.