Highly Efficient Blue Light-Emitting Diodes Enabled by Gradient Core/Shell-Structured Perovskite Quantum Dots

Room temperature (RT) synthesized mixed bromine and chlorine CsPbBr_<i>x</i>Cl_3-<i>x</i> perovskite quantum dots (Pe-QDs) offer notable advantages for blue quantum dot light-emitting diodes (QLEDs), such as cost-effective processing and narrow luminescence peaks. However, the efficiency of blue QLEDs using these RT-synthesized QDs has been limited by inferior crystallinity and deep defect presence. In this study, we demonstrate a precise approach to constructing high-quality gradient core-shell (CS) structures of CsPbBr_<i>x</i>Cl_3-<i>x</i> QD through anion exchange. Characterization shows that these CS-QDs exhibit a type-I band alignment with a high bromine concentration in the core and a high chlorine concentration in the shell. This unique configuration results in a larger exciton binding energy and reduced defect density, leading to enhanced exciton radiative recombination. Consequently, QLEDs using CS-QDs achieve an external quantum efficiency (EQE) of 16.28%, a maximum luminance of 8423.35 cd/m², and improved operational stability, surpassing the 12.80% EQE of reference QLEDs made with homogeneous structured QDs (HS-QDs). These findings present a strategy for developing high-quality RT-synthesized blue CS-QDs, marking a significant advancement in the field of efficient pure-blue QLEDs.