Photocarrier transport in regioregular poly(3-octadecylthiophene)

Charge carrier transport in regioregular poly(3-octadecylthiophene) has been studied by the time-of-flight method. The nature of transient photocurrent response is dispersive and holes were found to be the majority photocarriers with no detectable signal for electron transport. The hole mobility at room temperature and at an applied field of 1.3 x 10(5) V/cm has been measured to be 2.5 x 10(-5) cm(2)/V.s. Analysis of the transport mechanism confirms the predictions of the stochastic model of Scher and Montroll as indicated by the universal-scaling behavior of transient photocurrents when they were normalized with respect to transit time. The field and temperature dependence of hole mobility has been analyzed in terms of Poole-Frenkel and Bassler's Gaussian disorder model. The interpretation of the results of hole mobility measurement is made in terms of the concept of hopping among the polymer segments featuring a Gaussian distribution of energies with its variance of 74 meV.