Surface‐ and Spatial‐Regulated Cd‐Free Quantum Dots for Efficient, Mechanically Stable, and Full‐Color Flexible Light‐Emitting Diodes
Fan Cao, Qianqian Wu, Shizheng Zhang, Wenke Yu, Lingmei Kong, Yingguo Yang, Jiaqi Zhang, Sheng Wang, Xuyong Yang
Abstract
Flexible light-emitting diodes utilizing environmentally friendly cadmium (Cd)-free quantum dots (QDs) hold immense potential for next-generation wearable integrated displays. However, their overall performance lags behind Cd-based counterparts, and less research focuses on the suitability of QD layers in flexible devices. Herein, it is observed that the traditional surface oleate ligands on QDs readily detach under device operation after cycling bending, leading to increased surface defects and accumulated tensile stress in QDs layers, further diminishing their photoluminescence and electroluminescence performance. Based on these insights, a synergetic regulation strategy is developed employing a short-chain bidentate chelating ligand, diethyldithiocarbamate (DDTC), to strengthen the binding of QDs with ligands, minimizing ligand detaching and consequently inhibiting the non-radiative recombination of QDs; Meanwhile, the short-chain DDTC also reduces the inter-dot spatial distance and decreases the Young's modulus in QDs films, effectively dissipating stress localization and retaining the film morphology upon bending. Consequently, the resulting flexible devices based on blue ZnSeTe/ZnSe/ZnS QDs and green/red InP/ZnSe/ZnS QDs demonstrate the peak external quantum efficiencies of above 15% and maintain over 90% after 5000 bending cycles, rivaling state-of-the-art Cd-based flexible devices.