OLED Electron Injection Mechanism Explained

NHK Science & Technology Research Laboratories (NHK STRL) is conducting R&D on organic light-emitting-diode (OLED)¹⁾ devices, with the goal of realizing flexible, large-screen displays that can be folded or rolled up.

To extend the lifetime of flexible displays and reduce power consumption, NHK STRL has developed an electron injection layer (EIL) material, which injects electrons from the cathode into the light emitting layer²⁾. At this time, we give the first-ever explanation of the electron injection mechanism and have developed a new EIL material^* that will further improve performance.

To inject electrons into the light-emitting layer in an OLED device, the energy difference of approximately 2 eV between the cathode and the light-emitting layer must be reduced to zero. We have explained, for the first time, how the EIL material we have developed uses its chemical bonds with the neighboring material reduce this difference to zero. We have also explained how the electron transport material used in conventional OLED devices reduces this energy difference by approximately 1 eV, which is an even more important role than transporting the electrons. These discoveries have shown that with the new EIL material, the electron transport material is no longer needed, and it can inject electrons directly into the light-emitting layer.

The new EIL material will contribute to extending the lifetime and reducing power consumption of OLED devices and also simplify the structure of OLED devices, since the electron transport material is no longer needed.

These research results were published in the May 11 edition of Nature Communications. We are continuing R&D to create flexible displays with longer lifetime and lower power consumption as soon as possible.