Improved Ink-Jet-Printed CdSe Quantum Dot Light-Emitting Diodes with Minimized Hole Transport Layer Erosion

Ink-jet printing is a promising deposition technology, which is capable of large-area fabrication and mask-free patterning. For ink-jet-printed quantum dot (QD) light-emitting diodes (LEDs), the QDs are commonly dissolved in a mixture of solvent and thickener ink system. However, the hole transport layer could be eroded by this QD ink, leading to a rough surface morphology and resulting in the leakage of carriers and low device performance. This phenomenon was first and directly observed by using an atomic force microscope and a cross-sectional scanning electron microscope. We, therefore, redesigned the annealing process of the hole transport layer to achieve an optimized smooth surface with a reduced number of defects for ink-jet-printed QD LEDs (QLEDs). Optimized morphology brings back a maximum luminance of over 30,000 cd/m(2) and an external quantum efficiency of 7.52% for the ink-jet-printed red QLEDs using CdSe QDs, which are comparable to those of the spin-coated device. Moreover, the operation lifetime of the ink-jet-printed device is also enhanced by the restored surface morphology. An enhanced T-50 lifetime of the ink-jet-printed device at 1000 cd/m(2) is improved from 26 to 127 h, which converted to a long T-50 lifetime of 8013 h, when operated at 100 cd/m(2).

Automated summary

It was found that ink-jet printed QLEDs using quantum dot ink could erode the hole transport layer, resulting in rough surface morphology and decreased device performance. By optimizing the annealing process of the hole transport layer, a smooth surface with fewer defects can be achieved, improving device performance and lifetime.