Tuning Charge Transportation Balance in Quantum Dot Light Emitting Diodes by Decreasing the Mobility and Conductivity of In-DopedSnO2Nanocrystal Electron Transport Layer

Abstract

The use of quantum sized SnO₂ nanocrystals as the electron transportation layer (ETL) in quantum dot light-emitting diodes (QLEDs) has been demonstrated to be an effective method for improving device stability and eliminating the positive aging effect. However, compared to commonly used 4,4’-Bis(N-carbazolyl)-1,1’-biphenyl (CBP) hole transportation layer (HTL), the quantum sized SnO₂ nanocrystals usually possess a higher electron mobility and a higher conductivity, which results in the charge transport imbalance in QLEDs. Herein, In-doped SnO₂ quantum-sized nanocrystals are synthesized by the ligands-assisted solvothermal method. It was found that the mobility and conductivity of N-type In-doped SnO2 nanocrystals gradually decrease with increasing In doping concentration owing to the substitution of In3+ ions for Sn4+ ions as the electron acceptors. As a result, the charge transportation balance in QLED is realized by suppressing electron transportation ability of In-doped SnO₂ nanocrystals. A red inverted QLED based on 5 wt% In-doped SnO2 nanocrystal ETL exhibits a maximum luminance of 68,033 cd m-2, a current efficiency (CE) of 26.52 cd A-1 and an external quantum efficiency (EQE) of 18.94%. These results reveal that In-doped SnO2 nanocrystals are a promising candidate for fabricating high-performance and stable QLEDs.