Small molecule OLEDs (SMOLED) are able to achieve the smallest pixel pitch, but are more expensive to manufacture than Polymer OLEDs (PLED).
In the late 1970s, Dr. Ching Tang at Eastman-Kodak discovered a carbon compound that glowed in response to electric current. Small-molecule OLED technology was born. The first emissive material produced green light. During the 1980s, scientists at Kodak further improved on this technology, developing a portfolio of materials which were able to emit the spectrum necessary for a color display.
The emissive materials are deposited onto a glass substrate using a process known as vacuum deposition. In this process, the target material is evaporated at a high temperature and then condensed on the substrate in layers. For SMOLEDs, the substrate is typically glass, as the high temperatures involved make it impractical to use thin film substrates. Therefore, SMOLED displays are confined to rigid structures.
This manufacturing process is both complicated and expensive.
On color SMOLED displays, the emissive materials for the red, green, and blue materials are deposited separately. The regions where the material for each respective RGB subpixel is to be deposited are defined using a shadowmask. Practical limitations in the size and spacing of the openings in the shadowmask are the limiting factor in the density of the pixels on a SMOLED display. As of 2006, pixel densities of up to 450 ppi are possible.