Efficient and Stable Quantum‐Dot Light‐Emitting Diodes Enabled by Tin Oxide Multifunctional Electron Transport Layer

Abstract Zinc oxide (ZnO) based nanoparticles (NPs) are the most commonly used electron transport layer (ETL) materials in quantum dot light‐emitting diodes (QLEDs). However, numerous defects, severe quenching, and poor stability of ZnO NPs limit the commercialization of QLEDs. Herein, tin oxide (SnO 2 ) NPs are prepared as a substitute to ZnO. The obtained SnO 2 NPs exhibit high conductivity, good transparency, and excellent stability, thus enabling them to be applied as multifunctional ETLs for various structured QLEDs, e.g., 1) as a phase tuning layer to tune the microcavity effect in inverted QLEDs, 2) as a thick protection layer to improve the stability of noninverted QLEDs, 3) as a sputtering buffer layer to protect the functional layers from the ion bombardment damage in transparent QLEDs, and 4) as an internal light extraction layer to enhance the light coupling efficiency of top‐emitting QLEDs. With the multifunctional SnO 2 ETL, the resultant QLEDs are highly efficient (external quantum efficiency of 27.6%) and stable (half lifetime of 323 h at 4,459 cd m −2 ), which are comparable and even better than ZnMgO based devices. The results suggest that SnO 2 is a promising ETL material for realizing efficient and stable QLEDs.