Vertical organic field-effect transistors (VOFETs) have been explored with a higher current density, a faster switch speed, and a better air stability than conventional OFETs, which dramatically enhance the capability of driving an AMOLED backplane. Unfortunately, the state-of-the-art of the fabrication of solution-processed VOFETs is still very complicated, which can only focus at a single-cell level. In this work, with the assistance of the inkjet print, the fabrication process of a solution-processed VOFET was significantly simplified, and a solution-processed VOFET array was fabricated for the first time, which exhibited excellent device performance and outstanding mechanical stability. More importantly, the VOFET arrays exhibited excellent photodetector properties, and a flexible image sensor based on VOFET arrays with multipoint visible photodetection and image recognition was demonstrated for the first time. Therefore, this novel process dramatically simplified the VOFET device fabrication process and a successfully realized array, which promoted the commercialization of VOFET and showed great potential in flexible display, multifunctional sensors, and wearable integrated circuits.
Fabrication of metal oxide thin film transistor (MOTFT) arrays using the inkjet printing process has caused tremendous interest for low-cost and large-area flexible electronic devices. However, the inkjet-printed MOTFT arrays usually exhibited a non-uniform geometry due to the coffee ring effect, which restricted their commercial application. Therefore, in this work, a strategy is reported to control the geometry and enhance device performance of inkjet-printed MOTFT arrays by the addition of an insulating polymer to the precursor solution prior to film deposition. Moreover, the impact of the polymer molecular weight (MW) on the geometry, chemical constitution, crystallization, and MOTFT properties of inkjet-printed metal oxide depositions was investigated. The results demonstrated that with an increase of MW of polystyrene (PS) from 2000 to 200 000, the coffee ring was gradually faded and the coffee ring effect was completely eliminated when MW reached 200 000, which is associated with the enhanced viscosity with the insulating polymer, providing a high resistance to the outward capillary flow, which facilitated the depinning of the contact line, leading to the elimination of the coffee ring. More importantly, the carrier mobility increased significantly from 4.2 cm2 V−1 s−1 up to 13.7 cm2 V−1 s−1 as PS MW increased from 2000 to 200 000, which was about 3 times that of the pristine In2O3 TFTs. Grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy results indicated that PS doping of In2O3 films not only frustrated crystallization but also altered chemical constitution by enhancing the formation of the M-O structure, both of which facilitated the carrier transport. These results demonstrated that the simple polymer additive process provides a promising method that can efficiently control the geometry of MO arrays during inkjet printing and maximize the device performance of MOTFT arrays, which showed great potential for the application in next generation printed displays and integrated circuits.
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