Pure-Phase\nPerovskite Quantum Well for Green Light-Emitting\nDiodes

Perovskite\nmultiple quantum wells (MQWs) have shown great potential\nin the field of light-emitting diodes (LEDs). However, the random\nformation of QWs with varying well widths (<i>n</i> numbers)\noften leads to suboptimal interface defects and charge transport issues.\nHere, we reveal that the crystallization sequence of bromide-based\nperovskite MQWs is large-<i>n</i> QWs preceding small-<i>n</i> QWs. With this insight, we prevent the crystallization\nof subsequent small-<i>n</i> QWs by reducing the crystallization\nrate, ultimately resulting in the crystallization of only <i>n</i> = 5 QWs. This reduction in the crystallization rate is\nachieved through the chemical interaction of dual additives with perovskite\nconstituents. Additionally, the chemical interaction effectively passivates\nthe uncoordinated lead ions defects. Consequently, pure-phase perovskite\nQWs with a high photoluminescence quantum efficiency of 75% are achieved.\nThe resulting green LEDs achieve a peak external quantum efficiency\nof 17.1% and a maximum luminance of 29,480 cd m<sup>–2</sup>, which is attractive for full-color display applications of perovskites.