TCNQ Interlayers for Colloidal Quantum Dot Light‐Emitting Diodes

CdSe/CdS/ZnS quantum dot light‐emitting diodes (QD‐LEDs) show increased brightness (from ca. 18 000 to 27 000 cd m^?2) with 7,7,8,8‐tetracyanoquinodimethane (TCNQ) between the QD and electron‐transfer layers of ZnO nanoparticles. As QD/ZnO layers are known to have interface defects, our finding leads to the importance of interface engineering for QD‐LEDs. Although the photoluminescent intensity and decay lifetime of ZnO/TCNQ/QD layers are similar to those of ZnO/QD layers, cyclic voltammetry suggests improved charge transfer of TCNQ/ZnO layers compared to that of pure ZnO layers. This helps us to understand the mechanism of electrically driven QD‐LED behavior, which differs from that of conventional solid‐state LEDs, and enables the rational design of QD‐based optoelectronic devices.