Tuning charge transportation balance in quantum dot light emitting diodes by decreasing the mobility and conductivity of In-doped SnO2 nanocrystal electron transport layers

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 the 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 ligand-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 QLEDs is realized by suppressing the electron transportation ability of In-doped SnO2 nanocrystals. A red inverted QLED based on a 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.