Highly Stable SnO2-Based Quantum-Dot Light-Emitting Diodes with the Conventional Device Structure

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.