AIP Advances 3, 052125 (2013)

Scientists in China have fabricated a polymer light-emitting diode (LED) that is capable of emitting white light without using colour-converting phosphors, dyes or blends of several polymers. Their device contains a single thin layer of a polymer called PFB, which is interfaced to the hole transport material PEDOT:PSS and sandwiched between two electrodes. When driven at a few volts, the LED simultaneously emitted blue (490 nm) and red (620 nm) light. The blue emission is due to a conventional molecular lowest unoccupied molecular orbital–highest occupied molecular orbital transition in the material. In contrast, the longer-wavelength red emission originates from the creation of an electrically excited electromer state; it is found to be strongly dependent on the thickness of the PFB layer. Xinping Zhang and co-workers from Beijing University of Technology say that by tailoring the PFB thickness, the intensities of the blue and red emissions can be balanced, enabling the LED to emit white light.