Solvent‐Regulated Electronic Structure and Morphology of Inorganic Hole Injection Layers for Efficient Quantum Dot Light‐Emitting Diodes

Abstract

Inorganic charge transport layers (CTLs) have been proven to be effective for improving the stability of electroluminescent devices. However, the effective regulation of electronic structure for solution‐processed inorganic CTLs is still challenging by doping or interface engineering, and the film morphology is usually poor due to surface aggregation. Herein, the energy level and mobility of inorganic phosphomolybdic acid (PMA) hole injection layers (HILs) are regulated by adjusting the polarity of solvents, and the resulting inorganic HILs with proper electronic structure act as an energy ladder to better promote hole injection, thereby achieving balanced carrier transport in quantum dot light‐emitting diodes (QLEDs). Meanwhile, the surface morphology of the inorganic PMA film is also improved using solvents with high boiling points, which minimizes the surface tension and is conducive to the formation of smooth and pinhole‐free films. As a result, the devices using PMA dissolved in n‐butanol with a lower polarity exhibit a peak external quantum efficiency (EQE) of 19.2%, which is 3.6 times higher than that of QLEDs using PMA obtained from acetone solvent with a higher polarity. Herein, a general method for the deposition of high‐quality HILs for the fabrication of solution‐processed inorganic functional layers and optoelectronic devices is provided.

Keywords

• electroluminescence
• film morphologies
• inorganic hole injection layers
• light-emitting diodes
• quantum dots