Ultralow Doping in Organic Semiconductors: Evidence of Trap Filling

Investigation of the High Electron Affinity Molecular Dopant F6‐TCNNQ for Hole‐Transport Materials

“…E a decreases from 0.29 to 0.24 eV with as little as 1.0 mol% F6-TCNNQ, and further to 0.18 eV with 10.0 mol%. In analogy to previous work on n-doping of C 60 [33] and p-doping of CuPc, [25] this evolution is attributed to the filling and deactivation of trap and tail states by holes generated from the F6-TCNNQ molecules. As more dopants are introduced, E F moves toward the Spiro-TAD HOMO into a region of higher density of states where the activation energy for the hopping process is lower.…”

Role of band states and trap states in the electrical properties of organic semiconductors: Hopping versus mobility edge model

“…A recent study 55 , and compared it to the evolution observed in the UPS measurements. 37 As seen from Fig. 7b, a good match between the KMC simulation results and the experimental data is again obtained for both models.…”

“…35 However, there is now increasing evidence from a number of investigations that in many organic systems the deep gap states exhibit an exponential distribution. [1][2][3][4][5][36][37][38] These studies also suggest that the shallow trap states, i.e., the states located closer to the ME (or the valence band or conduction band edge) deviate from an exponential shape. For instance, very recent results obtained by means of scanning Kelvin probe microscopy on a self-assembled monolayer fieldeffect transistor (SAMFET) based on quinquethienyl molecules, reveal that the DOS consists of an exponential distribution of deep trap states with an additional group of localized shallow states that can be modeled via a Gaussian function.…”

“…36 A DOS that can be represented as a superposition of an exponential distribution and a Gaussian distribution has also been recently extracted from the carrier-concentration dependence of the conductivity in C 60 films. 37 A similar model was used as well to interpret the current-voltage dependence in poly(phenylene vinylene) and in a polyfluorene-based copolymer. 38,39 The purpose of the present work is to provide a detailed comparison of the hopping model and ME model in describing the effect of charge-carrier concentration on electrical conductivity, carrier mobility, and position of the Fermi level in the case of such a composite DOS.…”

“…Here, we apply both hopping and ME models to interpret the recent experimental data reported for n-doped C 60 films. 37 We note that the carrier concentration in these experiments is derived via a wellcontrolled n-type doping of the films whereby it can be assumed that each dopant provides one electron to the system; therefore, the electron concentration can be given in terms of the molar ratio (MR) of the dopant vs. host. The results obtained from the KMC simulations and from the ME model 19,20,46 are shown in Fig.…”