High‐Performance Bottom‐Contact Organic Thin‐Film Transistors by Improving the Lateral Contact

Abstract

prepatterned electrodes on the substrates generate artificial steps that significantly affect the morphological uniformity and continuity of the organic active layer at the electrode/organic interfaces, causing large contact resistance. The most common solution is to modify the electrodes, e.g., chemical bonding of thiols on gold, inserting buffer layer on the electrodes, or applying conductive materials such as graphene, polypyrrole as electrodes. [2,10, These approaches could either realize a good energy level alignment or improve the interface morphology to decrease the contact resistance. Nevertheless, the performances of the BC transistors are still insufficient to match the application requirements.It is known that the resistance of the transistors consists of channel resistance and contact resistance. The latter is determined by the carrier injection from the interfaces of the organic/electrode: the top injection and the side injection. [22] With regard to the side injection, a major issue is the morphology discontinuity near the edge of the electrodes. Previously, Kudo and co-workers proposed a method that embedding electrodes into the dielectric layer to achieve a planar interface and obtained a mobility ≈0.48 cm 2 V −1 s −1 (in saturate regime) for pentacene, but this will induce relatively complicate patterning process. [33][34][35] Li et al. treated the electrodes with fluorine substituted benzene thiol and effectively improved the texture from the contacts extending to thwe channel, as well as the performance of corresponding solution casted BC transistors. [30,36,37] Here, we report a simple method to improve the continuity of organic films at the lateral interfaces of electrode/organic through incorporating an organic inducing layer. Inserting an inducing layer has been widely applied in top contact transistors and received considerable attentions. [38][39][40] Herein, the organic layer which forms lamellar grains from the edge of the photolithographypatterned electrodes was deposited prior to depositing the active layer. The following organic semiconductor layer grown on the inducing layer formed lamellar films on the inducing layer, enabling a good contact between the electrodes and the organic semiconductor thin films. As a result, a remarkable decrement of the contact resistance is achieved. Together with the improved film ordering by weak epitaxy on the inducing layer in the channel area, we achieved high performance bottom contact thin film transistors with the maximum mobility exceeding 1 cm 2 V −1 s −1 for pentacene in ambient condition, which is comparable to the top contact ones.One of the main challenges to achieve high-performance bottom-contact transistors involves the organic/electrodes contacts. This study provides a simple approach to address the contact issue by incorporating an inducing layer prior to the organic semiconductor deposition. The molecules of the inducing layer nucleate into lamellar grains from the edge to the channel, resulting in a good morphological contact to th...

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

“…[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…”

Surface Catalytic Modification of Conjugated Polymer on Low‐Cost Bottom Contact for Improved Injection Efficiency of Organic Transistors

“…The difference of surface energy is not the reason that why the pentacene films have different morphology. The possible reason is that the PT on Ag electrode leads to smoother surface, and the π–π stacking between PT and pentacene induces the 2D layer by layer growth . It is worth mentioning that the contact angle of modified Ag is much larger than that of the Ag 2 O, which demonstrates that the improvement of performance in the experiment is not the effect of the oxidation of Ag electrodes …”

Surface modification with a fluorinated N-heterocyclic carbene on Au: effect on contact resistance in organic field-effect transistors

“…To overcome the high contact resistance in bottom contact OFETs, we applied a setting of V D = À100 V and V GS = 20 V to À100 V for the electrical characterizations. [41][42][43] Typically, contact resistance of an OFET is obtained through the transmission line model (TLM) method with the hypothesis that a series of devices have the same carrier transport properties in the channels. 44 Here a G-function method, an easy and rapid analytical approach with no assumptions regarding materials or device structures, was conducted for calculating the contact resistance by measuring output characteristics of an individual OFET.…”

“…To overcome the high contact resistance in bottom contact OFETs, we applied a setting of V D = −100 V and V GS = 20 V to −100 V for the electrical characterizations. 41–43…”