ZnO-based electron-transporting layers (ETLs) have been universally used in quantum-dot light-emitting diodes (QLEDs) for high performance. The active surface chemistry of ZnO nanoparticles (NPs), however, leads to QLEDs with positive aging and unacceptably poor shelf stability. SnO2 is a promising candidate for ETLs with less reactivity, but NP agglomeration in nonionic solvents makes the conventional device structure abandoned, resulting in QLEDs with extremely low operational lifetimes. The large barrier for electron injection also limits the electroluminescence efficiency. Here, we report one solution to all the above-mentioned problems. Owing to the strong HO-SnO2 coordination and the steric effect provided by the hydrocarbon groups, tetramethylammonium hydroxide can stabilize SnO2 NPs in alcohol, while its intrinsic dipole induces a favorable electronic-level shift for charge injection. The SnO2-based devices, with the conventional structure, exhibit not only the most efficient electroluminescence among ZnO-free QLEDs but also an operational lifetime (T95) over 3200 h at 1000 cd m-2, which is comparable with that of state-of-the-art ZnO-based devices. More importantly, the superior shelf stability means that the TMAH-SnO2 NPs are promising to enable QLEDs with real stability.
Keywords: positive aging; quantum-dot light-emitting diode; stability; tin oxide; zinc oxide.