The Monte Carlo Simulation Of Carrier Transport In Organic Polymers

In organic molecule, the electron-phonon interaction is very strong. When one organic molecule is occupied by one electron or hole, because of the electron-phonon interaction, the positions of atoms in that molecule will rearrange, forming a lattice deformation like a polaron, and this is called the lattice relaxation. Using Monte Carlo method, we have studied the transport properties of charge carriers in organic polymer and especially discussed the effects of lattice relaxation on the mobility. We also have given the analytic result in the one-dimensional organic molecular crystals.In a highly ordered, unimolecular organic molecular crystals, taking only latticerelaxation into consideration, we have obtained results that are conform to experimentalresults in large temperature and electric field region. When the electric field is small, themobility almost keeps constant. With the increasing electric field, the mobility increases atlow temperature, while decreases at high temperature. In the regioregularpoly(3-hexylthiophene)(P3HT), the same trend has been found in experiment. With the increasing temperature, the mobility first increases, and then decreases. When the reorganization energy is very large, the critical temperature is very large, so the decreasing trend can not be observed. In the same temperature region, with the reorganization energy getting larger, and getting close to the transfer integral, the dependence of mobility with temperature changes from increasing to decreasing. When the reorganization energy increases, the mobility decreases.In the disordered organic polymers, we discussed the effects of the position disorder, the energy disorder and the lattice relaxation on the carrier transport. We found that effects of the position disorder is very small, and can not change the trend of the carrier mobility of the electric field. The effects of energy disorder and the lattice relaxation are similar. The two different factors can cause the mobility change with the electric field and the temperature in the same trends, and the results we obtained are homology with experimental results. Using the lattice relaxation model, with all the disorders being neglected, we calculated the carrier transport in pentacene, especially the anisotropy of the carrier mobility. It is concluded that, the interaction of different molecular layers are small, so the symmetry of mobility in the single molecular layer is very well. However, the mobility in the c axis is about one third of the highest mobility, so the carrier transport in different molecular layers can not be ignored, and the carrier transport can not be regarded as a pure two-dimensional transport. In different direction, the temperature dependence of mobility is different. The model which is applied to the pentacene crystal is the small with the one used in the one-dimension organic molecular crystals, and all the results are conform to the experimental results, so the lattice relaxation is one of the important factors in carrier transport.