Self‐Assembled Molecule Doping Enables High‐Efficiency Hole‐Transport‐Layer‐Free Perovskite Light‐Emitting Diodes

Abstract Hole‐transport‐layer‐free (HTL‐free) perovskite light‐emitting diodes (PeLEDs) are attracting increasing research attention because of their simplified device structure, fast preparation process, and high cost effectiveness. However, their much lower external quantum efficiency (EQE) as compared with the conventional p‐i‐n type ones has considerably limited their application prospects. Here, a self‐assembled molecule (SAM) doping strategy is proposed by introducing [4‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl) butyl] phosphonic acid (Me‐4PACz) containing PO functional groups into the perovskite precursor solution and preparing the HTL‐free quasi‐2D perovskite films through the one‐step spin‐coating process. The doped Me‐4PACz molecules can not only accumulate at the ITO/perovskite interface to lower the hole injection barrier, but also extend deep into the perovskite layer to suppress the trap density in perovskite films and regulate the crystallization process for monodispersed phase composition. With the further addition of ethoxylated trimethylolpropane triacrylate small molecule containing CO groups to passivate the defects synergistically with Me‐4PACz, the EQE of the corresponding device is boosted from 1.5% to 16.7% together with a 3.5‐fold increase in operational stability, which is the highest efficiency reported so far for HTL‐free PeLEDs. The results demonstrate that the SAM doping strategy can be a viable and facile way to prepare high‐performance HTL‐free PeLEDs for practical applications.