Scientists from RIKEN, a RIKEN research institute in Japan, and the University of California, In collaboration with international partners, have shown a new way to manipulate excitons, which are essential for electronic transmission in OLeds. Their research shows that electron transport by exciton formation in OLeds can be controlled by manipulating the spin of electrons within the molecule. The discovery could significantly reduce the power consumption of OLeds.

Normally, excitons in OLeds come in two forms, the triple state and the singleton state. Singlet states require more energy. Although they can be converted to a triplet, the process of forming them requires more energy in the first place. The researchers found a way to lower the voltage in oleds so that they only form a triple state.

To better understand the physics behind exciton generation, the researchers used a scanning tunneling microscope combined with an optical detection system to perform precise single-molecule electroluminescence measurements. They prepared a model system based on the separation of organic semiconductor molecules, called 3,4,9, 10-tetracarboxylic anhydride (PTCDA), adsorbed on ultrathin metal-supported insulating films.
First, they put a negative charge on the organic semiconductor molecule. Then, using an electric current from a scanning tunneling microscope, they induced the molecules to glow and monitored which types of excitons were produced. The results show that only triplet state is formed under low voltage. Theoretical calculation also confirmed the experimental results.