Mixed ITO nanocrystal superlattice assembly. ITO nanocrystal superlattices were formed by a liquid-air interface assembly method. After cleaning a 2 cm × 2 cm Si substrate with Hellmanex (2 wt%) and acetone solution, 250 µL of water was dropped on the substrate. On top of the water droplet, 100 µL of nanocrystal dispersion was dropped. Nanocrystals were dispersed in the 2:1 mixture of hexane and toluene with the addition of 5 µL of oleic acid. The amount of 1% Sn and 6% Sn ITO nanocrystals were adjusted to the desired mixing ratio while maintaining the total nanocrystal concentration in the solution at 1 mg/mL. After depositing the nanocrystal dispersion, the substrate was partially covered with a glass slide to control the evaporation rate and convection flow. After evaporation of the solvent, the substrate was dried in air.