Charge carrier mobility in a two-phase disordered organic system in the low-carrier concentration regime

Abstract

In this paper we use a three-dimensional Pauli master equation to investigate the charge carrier mobility of a two-phase system which can mimic donor-acceptor and amorphous-crystalline bulk heterojunctions. By taking the energetic disorder of each phase, their energy offset, and domain morphology into consideration, we show that the carrier mobility can have a completely different behavior when compared to a one-phase system. When the energy offset is equal to zero, the mobility is controlled by the more disordered phase. When the energy offset is nonzero, we show that the mobility electric field dependence switches from negative to positive at a threshold field proportional to the energy offset. Additionally, the influence of morphology, through the domain size and volume ratio parameters, on the transport is investigated and an approximate analytical expression for the zero field mobility is provided.

Organic Optoelectronic Materials: Mechanisms and Applications

“…Woellner et al 504 used a similar approach to examine charge transport in a two-phase system in the low carrier density limit. They introduced an energy offset E offset between the average energies of two phases, each with a Gaussian-distributed DOS (less energetic phase being more ordered).…”

High Efficiency Dye-sensitized Solar Cells Constructed with Composites of TiO2 and the Hot-bubbling Synthesized Ultra-Small SnO2 Nanocrystals

“…This suggests a synergistic effect might occur between TiO 2 and SnO 2 , and this would provide advantages in enhancing the diffusion of charge carriers. On condition that measurements performed under the same lights and temperatures the mobility or concentration of charge carriers in bulk semiconductors is mainly determined by the band-gaps and Fermi levels 41 . Herein, we attributed the improvement to a shift of CBM due to the incorporation of SnO 2 , and the Fermi level in the composite is altered.…”

“…As is known, the band gaps can be enlarged by decreasing the size of a crystal. Due to the effective mass of electrons in SnO 2 is much lighter than those of holes ( m e * = 0.275 m e , m h * = 10 m e * , m e = 9.11 × 10 −31 kg), the CBM is raised prominently 28 38 , which uplifts the Fermi level of the semiconductor electrode 41 . The position of CBM in bulk SnO 2 is located at −4.56 V vs. vacuum 42 .…”

The Influence of Morphology on the Charge Transport in Two-Phase Disordered Organic Systems

“…We fixed σ 1 =σ 2= 0.1 eV and considered four different values of γ. For E offset >0 (here E offset =0.1 eV), the mobility has a negative field dependence followed by positive one [10]. The negative field dependence was discussed by Bässler [9] and Koster [6] in the context of a singlephase system.…”