Ambipolar transport of polymer semiconductors in diodes and carrier segment vibration relaxation to the negative slope phenomena

Abstract

After carefully theoretical research, as for the concepts of P- and N- type semiconductors, it is found that there are contradictions between inorganic and polymer semiconductors. Then through the basic concepts of hole and electron, it can be derived that all the polymer semiconductors should have ambipolar transporting characteristics, which has been proved by the subsequently experimental data through the impedance spectroscopy from the common materials. Such general ambipolar transporting properties of polymers are firstly systematically investigated in diode structure, which is closer to their intrinsic properties. The hole can be seen as “electron group of hole”, and it is difficult to be quenched than one electron, which can then help to get the common reported data that the number of hole transporting polymers are more popular than that of electron transport. Moreover, the experimental mobility curves mostly show the negative slope, which seems to be opposite to the basic fact that the electric field will accelerate the directional movement of carrier. The concept of carrier segment is then proposed for such negative slope, which is one conjugation projection system. In one carrier segment, the carrier can move freely as in one molecule, which can be accelerated by external electric field. From one carrier segment to another carrier segment, the kinetic energy of carrier could be relaxed by the vibration of carrier segment dipole. If the energy loss from vibration relaxation of carrier segment is larger than the energy increment from the external electric field, the carrier mobility curve will show the whole negative characteristic. Which effect can have the main influence is determined by the molecular structure of polymers. At last, the vibration model of the polymers has been investigated through the IR spectroscopy and the calculation methods. It is showed that the vibration models of P3HT have some special characteristics, which are corresponding to the fact that its slopes of hole and electron mobility curves are contrary to each other.