We report multilayer nanocrystal quantum dot light-emitting diodes (OD-LEDs) fabricated by spin-coating a monolayer of colloidal CdSe/CdS nanocrystals on top of thermally polymerized solvent-resistant hole-transport layers (HTLs). We obtain high-quality QD layers of controlled thickness (down to submonolayer) simply by spin-coating OD solutions directly onto the HTL. The resulting OD-LEDs exhibit narrow (similar to 30 nm, fwhm) electroluminescence from the QDs with virtually no emission from the organic matrix at any voltage. Using multiple spin-on HTLs improves the external quantum efficiency of the QD-LEDs to similar to 0.8% at a brightness of 100 cd/m(2) (with a maximum brightness over 1000 cd/m(2)). We conclude that QD-LEDs could be made more efficient by further optimization of the organic semiconductors.