Inkjet-printed multi-color arrays based on eco-friendly quantum dot light emitting diodes with tailored hole transport layer

Cadmium-free quantum dot light-emitting diodes (QLEDs) have held the potential to revolutionize the next-generation displays with their advantages in color gamut, luminance intensity, and solution processibility. As a promising way of realizing large-area QLED display production, inkjet printing has been intensively studied on Cd-based QLEDs but lacks exploration in fabricating Cd-free devices. Here, we developed Cd-free RGB inkjet-printed QLEDs with tailored hole transport layers (t-HTLs) using Cd-free QDs including InP/ZnSeS red and green QDs and ZnTeSe/ZnSe/ZnS blue QDs. With the t-HTLs, QD ink erosion on the bottom charge transport layer was remarkably suppressed, while the efficient hole transport was maintained, which kept high device performance, especially in the QLED lifetime. With bank structures, Cd-free QLED pixels were well defined within the size of 60 mu m x 160 mu m. Based on the t-HTL structure and the bank structures, inkjet-printed Cd-free RGB QLED pixel arrays were demonstrated. This study bridges the gap between existing Cd-free QLED technologies and the future commercialization of Cd-free self-emissive QD displays.