Probing Bulk Transport, Interfacial Disorders, and Molecular Orientations of Amorphous Semiconductors in a Thin‐Film Transistor Configuration

Abstract

Thin film transistors (TFTs) can be used to determine the bulk‐like mobilities of amorphous semiconductors. Different amine‐based organic hole transporting materials (HTs) used in organic light‐emitting diodes have been investigated. In addition, the present study also measures the TFT hole mobilities of two iridium phosphors: Ir(ppy)3 and Ir(piq)3. These materials are grown separately on SiO2 and polystyrene (PS). On SiO2, the TFT mobilities are found to be 1–2 orders smaller than the bulk values obtained by time‐of‐flight (TOF) technique. On PS gate dielectric layer, the TFT mobilities are in good agreement TOF data. Only 10 nm of organic semiconductor is sufficient for TFTs to achieve TOF mobilities. Using the Gaussian disorder model, it is found that on SiO2 surface, when compared to the bulk values, the energetic disorders (s) of the HTs increase and simultaneously, the high temperature limits (µ∞) of the carrier mobilities decrease. Both s and µ∞ contribute to the reduction of the carrier mobility. The increase in s is related to the presence of randomly oriented polar Si‐O bonds. The reduction of µ∞ on SiO2 is related to the orientations of the more planar molecules which tend to lie horizontally on the surface.

Using Ultralow Dosages of Electron Acceptor to Reveal the Early Stage Donor–Acceptor Electronic Interactions in Bulk Heterojunction Blends

“…The energetic disorder of holes remains in the range of 80–90 meV, while energetic disorder of electrons shows a substantial reduction from 122 to 62 meV. The reduction in electrons energetic disorder reflects a distinct change on energy width of the electron hopping site manifold, which arises from interactions with its environment . Using SCLC model with traps and GDM, we conclude that electron transport is the main factor that varies at different D–A weight ratio, and well‐correlated with OPV device performances.…”

A facile and robust approach to prepare fluorinated polymer dielectrics for probing the intrinsic transport behavior of organic semiconductors

“…From a plot of zerofield mobility (m 0 ) vs. (1/T) 2 , the slope can be used to extract s and the y-intercept represents m N . 42 Temperature dependent mobility measurements were carried out for all 4 electron acceptors, and their low field (linear) electron mobilities were extracted. From a plot of m 0 vs. 1/T 2 , the data can be seen to follow the GDM very well in all cases as shown in Fig.…”

Quasi-One-Dimensional Charge Transport Can Lead to Nonlinear Current Characteristics in Organic Field-Effect Transistors

“…However, recently, the direct applicability of conventional device models to the evaluation of the mobility in this method has been put into question and has severely impacted organic semiconductorrelated studies. 8,9 For an OFET device, the charge mobilities are generally reported in the saturation regime, 10 even though it has been documented that it is preferable to use the linear regime for their evaluation. 9 The OFET saturation current (I D,sat ) is expressed as 11…”

“…For an OFET device, the charge mobilities are generally reported in the saturation regime, even though it has been documented that it is preferable to use the linear regime for their evaluation . The OFET saturation current ( I D,sat ) is expressed as where W denotes the channel width, L the channel length, C i the dielectric surface capacitance and V G , V D , and V T the gate voltage, drain voltage, and threshold voltage, respectively.…”