Engineering Asymmetric Charge Injection/Extraction to Optimize Organic Transistor Performances

Abstract

The introduction of an appropriate functionality on the electrode/active layer interface has been found to be an efficient methodology to enhance the electrical performances of organic field-effect transistors (OFETs). Herein, we efficiently optimized the charge injection/extraction characteristics of source/drain (S/D) electrodes by applying an asymmetric functionalization at each individual electrode/organic semiconductor (OSC) interface. To further clarify the functionalizing effects of the electrode/OSC interface, we systematically designed five different OFETs: one with pristine S/ D electrodes (denoted as pristine S/D) and the remaining ones made by symmetrically or asymmetrically functionalizing the S/D electrodes with up to two different self-assembled monolayers (SAMs) based on thiolated molecules, the strongly electron-donating thiophenol (TP) and electron-withdrawing 2,3,4,5-pentafluorobenzenethiol (PFBT). Both the S and D electrodes were functionalized with TP (denoted as TP-S/D) in one of the two symmetric cases and with PFBT in the other (PFBT-S/D). In each of the two asymmetric cases, one of the S/D electrodes was functionalized with TP and the other with PFBT (to produce PFBT-S/TP-D and TP-S/PFBT-D OFETs). The vapor-deposited p-type dinaphtho[2,3-b:2′,3′f ]thieno[3,2-b]thiophene was used as the OSC active layer. The PFBT-S/TP-D case exhibited a field-effect mobility (μ FET ) of 0.86 ± 0.23 cm 2 V −1 s −1 , about three times better than that of the pristine S/D case (0.31 ± 0.12 cm 2 V −1 s −1 ). On the other hand, the μ FET of the TP-S/PFBT-D case (0.18 ± 0.10 cm 2 V −1 s −1 ) was significantly lower than that of the pristine case and even lower than those of the TP-S/D (0.23 ± 0.07 cm 2 V −1 s −1 ) and PFBT-S/D (0.58 ± 0.19 cm 2 V −1 s −1 ) cases. These results were clearly correlated with the additional hole density, surface potential, and effective work function. In addition, the contact resistance (R C ) for the asymmetric PFBT-S/TP-D case was 10-fold less than that for the TP-S/PFBT-D case and more than five times lower than that for the pristine case. The results contribute a meaningful step forward in improving the electrical performances of various organic electronics such as OFETs, inverters, solar cells, and sensors.

Reduced Threshold Voltages and Enhanced Mobilities in Diketopyrrolopyrrole–Dithienothiophene Polymer‐Based Organic Transistor by Interface Engineering

“…[ 21,32,34,37 ] Almost one order magnitude improvement of the hole mobility and a switching from the hole accumulation mode ( V th = −3.75 V) to depletion mode ( V th = +1.06 V), upon PFBT treatment of Au contact in BC OFETs having OTS‐treated SiO 2 , which is an interesting observations in our investigation. [ 36 ]…”

“…[ 5,21,32,33 ] Pentafluorobenzene thiol (PFBT) treatment has been one of the most widely used metal interface modifying SAM material. [ 34–37 ] Most recently, OFET's electrical characteristics variation under the presence of interface modifications done simultaneously at both barriers, for a given organic semiconductor material, has emerged as a promising approach. [ 34–37 ]…”

“…[ 34–37 ] Most recently, OFET's electrical characteristics variation under the presence of interface modifications done simultaneously at both barriers, for a given organic semiconductor material, has emerged as a promising approach. [ 34–37 ]…”

Electrode and dielectric layer interface device engineering study using furan flanked diketopyrrolopyrrole–dithienothiophene polymer based organic transistors

“…This will make the charge injection from the respective electrode adjustable based on the band gap of the respective organic semiconductor material 24 . Adjusting the work function of an electrode is critical to modulate the charge transport and electrical performance because the threshold voltage (V th ) shifts in OFETs is influenced by the intrinsic electric field produced by the permanent dipole of the SAM layers and by the electrochemical reaction between surface functional groups and the semiconductor molecules 25 . Basically, both such modifications can variably influence the crystallization process of the active layer, in terms of molecular packing and grain boundary sizes independently.…”

“…Basically, both such modifications can variably influence the crystallization process of the active layer, in terms of molecular packing and grain boundary sizes independently. Thereby, the study of their combined effect with proper reasoning about the underlying physics, on some of those high performing organic semiconductor based OFETs has become essential [24][25][26][27] .…”