Scientists from the RIKEN center in Japan have found a new way to make OLEDs, using electrospray-deposited polymer films, which they say have better characteristics than OLEDs made from spin-coated films. The researchers have used a novel dual-solvent concept to make the electrospray-deposited films smoother than before, thereby enabling the superior devices to be built.
Previous attempts to use the electrospray-deposition technique for OLED fabrication have failed to produce polymer films that compete with other fabrication techniques. Yutaka Yamagata of the RIKEN Center decided to use a combination of two solvents to improve this technique, which uses a thin glass capillary with the polymer solution stored inside and a conductive wire inserted in it. When a high voltage is applied between this conductive wire and the OLED electrodes on the substrate, the solution sprays out of the capillary end as atomized droplets that are attracted to the substrate by electrostatic force. This means there is little solution wastage as the spray is highly directed.
From a series of comparative experiments, the researchers found that devices fabricated from electrospray-deposited films turned on at lower voltages and could support higher current densities than ones made from spin-coated films. At low voltages, the electrospray deposition also enabled higher pixel intensity.
“We have discovered a range of conditions using a two-solvent method that can make extremely smooth thin films using electrospray deposition,” says Yamagata. “Using this technology these devices could be manufactured as inexpensively as printing newspapers.”