Scattering Process Between Polaron And Triple Exciton In Crystalline Organic Semiconductor Under External Magnetic Field

In2003, Jan Kalinowski et al found the OMEL effect in the crystalline organic semiconductor--Alq3. Since then, similar experiments also demonstrated this complex phenomenon. First of all, we will introduce the basic mechanism of Organic Light Emitting Diode(OLED):negative and positive electrons inject the organic semiconductor layer from both ends of the negative and positive electrodes, which gradually form the negative and positive polarons, at the same time as the driving effect of external electric field, positive and negative polarons collide, composite and form excitons at last. According to the different combinations of spins, excitons are divided into two kinds--singlet excitons and triplet excitons. Only the singlet excitons can emit a photon to light, at the same time returning to the ground state; and triplet excitons are not able to directly light. However, triplet excitons have a long life span, and their ratio is much higher than singlet excitons, theoretically, they respectively account for3/4and1/4of the total excitons. So, triplet excitons will have greater odds to scatter the polarons than the singlet excitons. The current academic gains have proved that the scattering process between the polaron and triplet exciton can generate the singlet exciton and the excited polaron, both of which are benefited to the electroluminescence process. The existing experiments also observed the positive OMEL effect. This means that the magnetic field also promotes the electroluminescence effect. But under external magnetic field, the concrete scattering process between triplet exciton and polaron still has not been detailedly researched; whether this process really makes the yield of singlet exciton or excited polaron bigger has still not been discussed yet. This paper mainly discusses this problem.In crystalline organic semiconductor, considering hyperfine interaction, using the one-dimensional tight binding approximate SSH Hamiltonian model and the nonadiabatic molecular dynamics method of evolution, we simulate the scattering process between a triplet exciton which spin is up and a negative polaron which spin is down under different magnetic field, and find out the main products. The role of the magnetic field is to produce the split of the energy level and to regulate the hyperfine interaction. And our results show that:with the increase of magnetic field, the yield of singlet exciton and excited polaron will both become larger. This also do prove the magnetic field will cause the positive OMEL effect.