Surface functionalization of ZnO nanoparticles with sulfonate molecules as the electron transport layer in quantum dot light-emitting diodes

ZnO nanoparticles (NPs) with excellent optoelectronic properties are widely used as electron transport layers (ETLs) in quantum dot light-emitting diodes (QLEDs). However, the high conductivity of ZnO can lead to charge imbalance and exciton quenching at the emission layer (EML)/ETL interface, seriously limiting the device performance. In this research, three phenylated sulfonate ligands, including sodium benzenesulfonate (SBS), sodium p-toluenesulfonate (STS), and sodium beta-styrenesulfonate (SβSS), were solely introduced onto the ZnO NP surface. Smooth and compact surfaces of ZnO films were obtained after introducing phenylated sulfonate ligands. Additionally, an upward shift in the energy levels of ZnO was observed, leading to a reduction in electron transport and thereby alleviating excess electron injection. The optimized QLED using the SβSS-modified ZnO ETL exhibited the best performance with a maximum luminance of 458 810 cd m⁻² and a peak current efficiency of 40.1 cd A⁻¹, which were enhanced by 60.6% and 64.1% compared with those of the control device based on the pristine ZnO ETL. Meanwhile, an extrapolated device lifetime exceeding 1073 hours was anticipated that was 9.3-fold longer than that of the control device. Our experiments demonstrate the impact of phenylated sulfonate molecules on the surface modification of ZnO NPs and the performance of QLEDs, providing valuable insights and support for future developments.