Additively Manufactured Organic Field Effect Transistors for Cascadable Circuit Design

Additively manufactured organic electronics suffer from poor electrical performance such as hysteresis and low mobility, which makes it difficult to be used in the cascaded circuits. The factors responsible for the poor performance include the non-uniformity of the printed pattern as the discontinuous films can suppress charge transport. Besides, poor film morphology such as a non-compact and rough dielectric layer, leads to severe leakage current and poor hysteresis in organic effect field effect transistors (OFETs). The poor organic semiconductor (OSC) crystallinity and the charge carrier traps at the OSC/dielectric interface will also impede the charge transport and cause poor electrical performance. In addition, the resolution and accuracy of the printing technology also need to be optimized in order to achieve printed high performance OFETs.

Here, improved OFET performance was achieved with respect to the printing technology and film quality. For the printing method, solution-sheared extrusion-based Direct Ink Writing (DIW) was employed for OFET fabrication and achieved highly ordered crystal morphology of OSC. The OFET with DIW printed OSC shows hysteresis-free transfer and output curves, low threshold voltage and good long term air stability. Therefore, the extrusion-based DIW offers a new way to print organic transistors, as well as the cascaded circuits. Besides, improved film quality in OFET was achieved by simultaneously controlling the growth process of the semiconductor and the dielectric. In order to simultaneously enhance the film quality of the printed dielectric and OSC, a geometric molecule search was developed to computationally discover the high-performance bifunctional molecule based on the chemical characteristics. This geometric molecule search opens a new way for exploring appropriate interface engineering molecules to improve the electrical performance of OFETs as well as other organic devices, such as organic solar cells and light-emitting diodes. One of the bifunctional molecules resulting from geometric search is trimethoxyphenylsilane (TMPS), which was applied in OFET fabrication for the first time and promoted long range ordered OSC as well as simultaneously reduced charge traps on the dielectric surfaces. As a result, the electrical performance of printed OFET was further improved with TMPS treatment and a three-stage ring oscillator was successfully built. Thus, TMPS provides a new way to engineer the printed dielectric/semiconductor interface and control the crystallinity of the OSC in OFETs and cascaded circuits.