Polymer Sub-exciton Collision Process Studies, Polarization

In organic light-emitting devices, the electrons and holes are injected into the polymer from the electric diodes and then they form negative and positive polarons. Under the influence of electric fields, some of the negative and positive polarons will collide, combine and form excitons. The exciton formed by a polaron pair may be singlet or triplet. The singlet exciton can return to the ground state through emitting a photo so its life is short. The triplet exciton is not light-emitting, so its life is long. Therefore, a polaron may collide with the triplet exciton at high probability. This collision between the polarons and the triplet exciton is believed to be of fundermental important for the charge transportation and the efficiency of electroluminescence. In the paper, based on the one-dimensional tight-binding Su-Schrieffer-Heeger(SSH) model, by using a nonadiamatic molecular dynamic method, we simulate collision of a negative polaron and a triplet exciton in one polymer chain.The results of our simulations show that the lattice structure and the electronic state of the polaron and the exciton are changed very much in the collision process. Firstly, at lower electric field ( E₀≤0. 11×10⁵V/cm), the polaron will combine with the exciton when they collide. Secondly, at mediate field strength ( 0 .12×10⁵ V /cm≤E₀≤2.7×10⁵V/cm), the polaron and the exciton will go across each other and both of them have a"phase shift''at the point of collision. In the process of the collision, the lattice oscillated by large amplitude and at the same time an energy level appeared in energy gap. This means that there are new localized states are excited due to the collision. It should be stressed that the yield of singlet exciton in the process is very low, it is about 1%. Thirdly, In stronger field strength ( E₀≥2. 8×10⁵V/cm), the polaron will be dissociated after the collision with the exciton.