On the Nature of Charge-Injecting Contacts in Organic Field-Effect Transistors

Abstract

Organic field-effect transistors (OFETs) are key enabling devices for plastic electronics technology, which has a potentially disruptive impact on a variety of application fields, such as 2 health, safety and communication. Despite the tremendous advancements in understanding the OFET working mechanisms and device performance, further insight into the complex correlation between the nature of the charge injecting contacts and the electrical characteristics of devices is still necessary. Here, an in-depth study of the metal-organic interfaces that provides a direct correlation to the performance of OFET devices is reported.The combination of synchrotron x-ray spectroscopy, atomic force microscopy, electron microscopy, and theoretical simulations on two selected electron transport organic semiconductors with tailored chemical structures allows to gain insight on the nature of the injecting contacts. This multiple analysis repeated at the different stages of contact formation provides a clear picture on the synergy between organic/metal interactions, interfacial morphology and structural organization of the electrode. The simultaneous synchrotron x-ray experiments and electrical measurements of OFETs in operando uncovers how the nature of the charge injecting contacts has a direct impact on the injection potential of OFETs.

Improving Charge Injection at Gold/Conjugated Polymer Contacts by Polymer Insulator‐Assisted Annealing for Transistors

“…Currently, in organic electronics, metal layers are usually deposited on organic films via thermal evaporation to form electrodes, while metal deposition process inevitably leads to disorders of organic surface and even damages the chemical structures. [22][23][24] It is generally believed that, besides the energy level mismatch produced injection barrier, the disorders and damages increase the contact resistance, which is disturbing for obtaining an ideal metal/organic contact interface. [22][23][24][25] Several methods have been proposed to reduce the contact resistance and improve charge injection at metal/organic interface, such as contact doping, introducing a charge injection layer, or forming an abrupt damage-free metal/semiconductor interface by transferred electrodes.…”

“…[22][23][24] It is generally believed that, besides the energy level mismatch produced injection barrier, the disorders and damages increase the contact resistance, which is disturbing for obtaining an ideal metal/organic contact interface. [22][23][24][25] Several methods have been proposed to reduce the contact resistance and improve charge injection at metal/organic interface, such as contact doping, introducing a charge injection layer, or forming an abrupt damage-free metal/semiconductor interface by transferred electrodes. [2,5,[24][25][26][27][28][29][30] However, these methods require additional and complicated processes, which increase the difficulty of device fabrication and some of them also…”

Toward Efficient Charge Transport of Polymer-Based Organic Field-Effect Transistors: Molecular Design, Processing, and Functional Utilization

“…From the viewpoint of composite atoms, a high proportion of highperformance semiconducting polymers contain S atoms in their backbones. Upon utilizing Au as the electrode material, these S atoms could facilitate Au−S binding 19 through physical/chemical absorption and may contribute to charge injection. Compared to their p-type counterparts, the n-type or ambipolar semiconducting polymers generally have inferior carrier mobility and stability.…”

2,3-Thienoimide-ended oligothiophenes as ambipolar semiconductors for multifunctional single-layer light-emitting transistors

“…In this context, the same NT4N-based device was recently used to provide further insight into the complex correlation between the nature of the charge-injecting contacts and the electrical characteristics of devices. 89 The authors showed how the presence of thienyl sulfur atoms in NT4N determined the formation of chemical interactions with gold electrodes, with the consequent formation of small gold nanoclusters during the first stages of contact formation. Multiple analyses repeated at different stages of device fabrication, including also synchrotron X-ray spectroscopy on devices in operando, showed that the electrical performance was the result of the interplay between (i) the chemical composition of metal electrodes and the OSC, (ii) the type of physicochemical interactions at the metal/OSC interface, (iii) the interfacial morphology and (iv) the organization of the metal clusters at the OSC interface.…”