New technology employs organic light emitting diodes, or OLEDs, tiny thin films that create light in response to electrical current. But making OLED displays that are much bigger than a smart phone’s has been problematic. While they consume less power overall, a serious burst of current is needed to fire up each pixel. Transistors that provide this much current are bulky and take up valuable screen space; they also require elaborate, expensive construction and yield pixels that aren’t uniform, a problem that grows with display size.
To skirt these issues, Rinzler and his colleagues used a network of carbon nanotubes to drive current. The nanotube layer is porous, letting light through, so the transistor and light-emitting layers can be stacked vertically instead of sitting side-by-side, saving real estate. Without having to squeeze in transistors right next door to the OLEDs, more area is devoted to emitting light. In fact, 98 percent of the device emits light.
Intrinsic nonuniformity in the polycrystalline-silicon backplane transistors of active matrix organic light-emitting diode displays severely limits display size. Organic semiconductors might provide an alternative, but their mobility remains too low to be useful in the conventional thin-film transistor design. Here we demonstrate an organic channel light-emitting transistor operating at low voltage, with low power dissipation, and high aperture ratio, in the three primary colors. The high level of performance is enabled by a single-wall carbon nanotube network source electrode that permits integration of the drive transistor and the light emitter into an efficient single stacked device. The performance demonstrated is comparable to that of polycrystalline-silicon backplane transistor-driven display pixels.