QLED and preparing method thereof, and display device and preparing method thereof

An embodiment of the invention provides a QLED and a preparing method thereof, and a display device and a preparing method thereof, which relate to the technical field of display, and can avoid a functional layer of an organic material positioned below a quantum dot layer from being corroded and enable the quantum dot layer to be uniform in film forming. The preparing method of the QLED comprises: forming a first electrode, a first functional layer, the quantum dot layer, a second functional layer and a second electrode on a base substrate in sequence; after the first functional layer is formed from the organic material and before the quantum dot layer is formed, the preparing method further comprises: forming a buffer layer made from a polar organic solvent; on the basis, forming the quantum dot layer which includes: forming a solution containing quantum dots and a nonpolar organic solvent above the buffer layer by adopting an ink-jet printing manner; evaporating the solvent by an evaporation process to form the quantum dot layer. The preparing method is used for the QLED.