<p>The PN junction of semiconductors plays an important role in designing and developing light-emitting diodes. In contrast, the characteristics of PN junctions in quantum dot light-emitting diodes (QLED) have been less discussed. In this work, we analyzed the current-voltage (I–V) characteristics of QLED using a modified nano-PN junction model, which combines a silicon-based PN junction model and a hopping transport model. Under the assumption of recombination current dominance in high-efficiency QLEDs, the correlations between complete QLED I–V curves and their constituent sub-device characteristics were derived. The voltage distribution and Quasi-Fermi level splitting of functional layers were performed to elucidate the high ideality factors of QLED devices. The nanocrystal-based PN junction model was extended to simulate the experimental I–V curves of efficient QLED devices. In all, this work not only deepens the device understanding into QLED from the view of semiconductor physics, but also builds up a theoretical framework of nanocrystal-based PN junctions.</p>