Surface modification of printed silver electrodes for efficient carrier injection in organic thin-film transistors

Abstract

The modification of printed silver electrode surfaces for use as the bottom-contact electrodes of organic thin-film transistors (OTFTs) is reported. Printed silver electrodes fabricated using the surface photoreactive nanometal printing (SuPR-NaP) technique are inevitably covered with an inert surface layer of alkylamines that is originally used for encapsulation of the silver nanoparticles (AgNPs). However, it may act as a built-in protective layer against carrier injections. We demonstrate that a simple vapor exposure method is sufficient for converting the protective layer into a layer that assists carrier injection. As modifiers, we used various types of fluorinated benzenethiols that exhibit a stronger coordination with the silver surfaces than the alkylamimes. We detected the chemical conversion from alkylamine encapsulation to thiol coordination by surface enhanced Raman spectroscopy (SERS) and evaluated the improvement in the carrier injection using a transfer length method (TLM) for the OTFTs. Among the modifiers, the pentafluorobenzenethiol (PFBT) treatment significantly improves the device performance and stability of the OTFTs.

Silver Nanoparticles Based Ink with Moderate Sintering in Flexible and Printed Electronics

“…Furthermore, a bottom contact device structure was usually used in these devices, where the source-drain electrodes were printed prior to channel layer. The surface of printed Ag NPs electrodes could be modified to increase work function and improve electrode contact with channel layer, so as to improve device performance [125,126,127,128].…”

Inner‐Evaporator Modification of Low‐Cost Metal Electrodes of Organic Field‐Effect Transistors by 2D Polyporphyrin

“…The devices with modified Cu electrodes show similar results (Figure S4, Supporting Information) with Ag. The mobilities are among the highest values of pentacene thin‐film bottom‐contact OFETs based on modified Ag/Cu electrodes (0.11–0.8 cm 2 V −1 s −1 , Figure e), and even comparable to that of the devices with modified Au electrodes (around 1 cm 2 V −1 s −1 ) …”

“…Meanwhile, the polymerization only happens on the surface of the metal electrodes while the excessive Br‐TPP monomers on the electrodes and channel regions are removed by heating the substrate, leading to surface‐confined PP film with 1.1 nm thickness on the electrode and a clear surface on the channel. As a result of the clean interface, ultrathin thickness of PP as well as optimized pentacene morphology, the contact resistance decreases by 2–3 orders of magnitude compared with the contaminated and unmodified ones, and the mobilities of pentacene OFETs increase by ≈2 orders to a value up to 0.93 cm 2 V −1 s −1 (PP modified Ag) and 0.59 cm 2 V −1 s −1 (PP modified Cu), which is one of the highest values in pentacene thin‐film bottom‐contact OFETs based on modified Ag/Cu electrodes, and even comparable to modified Au electrode …”

“…However, in most cases, especially in the industry‐compatible bottom‐contact configuration, the electrode/semiconductor contact is Schottky type instead of the ideal Ohmic type, which brings high contact resistance and deteriorates the device performance . To solve the problem, much effort has been dedicated to improving the electrode/semiconductor interfacial contact, such as modifying self‐assembled monolayer (SAM) on metal electrodes or inserting other interlayers into the electrode/semiconductor interface. For instance, Kim et al modified the metal electrodes in thiol compound solutions to improve the device mobility .…”

“…However, recent approaches are normally complicated and suffer from either solution‐involved process or high‐temperature conditions, which require environmentally unfriendly and contamination‐containing chemicals or operations. These disadvantages become more critical when it comes to the low‐cost Ag or Cu electrodes, because Ag or Cu are easily oxidized and contaminated in the above processes compared with Au electrodes, leading to limited application of low‐cost electrodes in OFETs. Thus, developing a simple modification method that prevents potential contaminations or damages to the electrodes is of great importance for high performance OFETs based on low‐cost electrodes.…”