Solution-processed ZnO quantum dot thin films with low solvent residues and ultra-flat surfaces

ZnO quantum dots are considered a desirable material for the electron transport layer (ETL) in thin-film optoelectronic devices, determining their efficiency and stability. Solution-processed ZnO quantum dot films are fascinating due to the potential for low-cost manufacture of large-area devices and the compatibility with flexible substrates. However, eliminating solvent residues from solution-derived ZnO films remains a challenge, as their presence can significantly impact the efficiency and performance of the devices. Herein, we reported a straightforward and controllable strategy to overcome the above problem, aiming to achieve low solvent residues and ultra-flat ZnO films. Methanol, with its low boiling point and high relative evaporation rate, is utilized as a dispersing solvent for ZnO quantum dots, the resulting thin films exhibit low solvent residue, as confirmed by TGA and NMR analyses. Moreover, we achieved a stable monodisperse state of ZnO quantum dots in methanol solvent for three months by a simple temperature control method. The ZnO film prepared using a low-temperature spin-coating technique demonstrates extremely low surface roughness (RMS less than 1 nm). [Display omitted] •Different solvent residues in ZnO quantum dot films were investigated.•The impact of solvent chain length on the dispersibility of ZnO quantum dots was examined.•The stable dispersion of ZnO quantum dots in methanol solution for up to 3 months was successfully achieved.•Lower surface roughness of ZnO film was obtained by spin coating at low ambient temperature.