An inkjet printed quantum dot (QD) color conversion layer needs to be a few micrometers thick to successfully block blue light leaking from the organic light‐emitting diode (OLED). To control the thickness of the QD film in the pixel, we investigated modifying the surface wettability of both the substrate and bank by hydrophobic octadecyltrichlorosilane (OTS) treatment. Without the OTS treatment, the printed QD droplets came to the bank before the pinning process and excessive pile-up occurred, pushing them over the bank wall. However, with OTS surface treatment, the contact angle of the QD ink was increased from 16° to 38° on the substrate and from 59° to 89° on the bank. By reducing the contrast in hydrophilicity and hydrophobicity between the substrate and bank, the pile-up phenomenon was remarkably reduced. This allowed us to control the thicknesses of the QD layers by changing the number of printed drops of QD ink. As the thickness of the QD film increased from 1 μm to 9 μm, the CIE chromaticity coordinates of the spectrum changed from (0.173, 0.437) to (0.265, 0.648) moving from sky blue-green to nearly pure green.
