Enhanced Efficiency of InP-Based Quantum Dot Light-Emitting Diodes Using P-Type Inorganic Nanoparticles

Quantum dot (QD) light-emitting diodes (QLEDs) have attracted attention as one of the promising candidates for next-generation displays. In QLEDs, device efficiency tends to be limited by inefficient hole injection induced by large energy barrier between a QD emission layer (EML) and a common hole transport layer (HTL). The energy barrier can be tuned by adopting p-type semiconductor materials with proper valence band maximum (VBM) energy levels close to the QD EML. Herein, we introduce efficient InP-based red QLEDs in an inverted structure with p-type inorganic nanoparticles within the QD EML. Ultraviolet photoemission spectroscopy (USP) measurement revealed that the VBM of the QD EML was upshifted by 0.2 eV from 6.7eV to 6.5eV when nickel oxide nanoparticles were mixed into the QD EML, which leads to improvement of the hole injection and suppression of the excess electron injection into QDs. As a consequence, we successfully demonstrated QLEDs exhibiting a maximum external quantum efficiency of 4.7% and a maximum luminance of 16770 cd/m2, which are higher by 1.5-fold and 1.4-fold, respectively, compared with those of pristine QLEDs. The results elucidate that introducing a small amount of p-type inorganic nanoparticles into the QD EML could be a simple and effective way to improve hole injection in QLEDs.