Printed P-Channel, Transparent Thin-film Transistors Fabricated at Room Temperature
Scientists at Dongguk University have devised a way to produce printed p-channel thin-film transistors using the plentiful and environmentally-friendly copper iodide semiconductor at room temperature. They assert that their energy-efficient and cost-effective fabrication technique for these transistors may lead to the development of low-cost and novel optoelectronic devices.
Research into the fabrication of new types of semiconducting materials for thin-film transistors (TFIs) has been ongoing for decades. Whenever new transistor configurations or novel fabrication methods are devised, many previously impossible applications can become feasible, such as ultrahigh-definition transparent displays and flexible electronic devices.
The researchers noted that now, p-type transparent semiconductors for making p-channel transistors are in huge demand. Such semiconductors are conductive due to the movement of charge carriers called "holes." While these transistors are in great demand, when compared to their n-type counterparts, their use is restricted because of chemical instability and poor electric properties.
To overcome these limitations, a research team at Dongguk University led by Prof. Yong-Young Noh concentrated on using a p-type transparent semiconductor for TFTs using a metal halide-like copper iodide (CuI), instead of metal oxide.
Printed p-channel, transparent thin-film transistors fabricated at room temperature. (click on image to enlarge)
"The naturally abundant and environmentally-friendly constitutional elements of CuI make it more appropriate for large-scale printed transparent electronics. More importantly, CuI has a higher hole mobility than other p-type oxide-based semiconductors," explained Prof. Noh.
However, CuI had been rarely used as a semiconductor for TFTs because its hole concentration is so high that it tends to make uncontrollable conductivity. Transistors are generally meant to be switchable from a conductive to a non-conductive state to be readily turned on an off at high speeds.
Furthermore, standard solution-based processing for making thin films usually requires a heat treatment called "annealing," which tends to be both energy- and time-consuming.
The researchers found that they could reduce the conductivity of CuI-based thin films by making them even thinner, thereby suitable for fabricating TFTs with the performance currently demanded for numerous applications. Moreover, these CuI thin films do not require any annealing and can be processed at room temperature, thus saving energy and making them more economical.
The team tested multiple processing conditions and fabricated various TFTs to determine the source of the enhanced device properties and to demonstrate the potential uses of CuI as a thin-film p-type semiconductor.
"We believe that this work opens the floodgate for room-temperature, low-cost, printed transparent p-type transistors for diverse optoelectronic devices," concluded Prof. Noh.
Reference
Liu, A. Zhu, H., Park, W., et al. Room-Temperature Solution-Synthesized p-Type Copper(I) Iodide Semiconductors for Transparent Thin-Film Transistors and Complementary Electronics. Advanced Materials, 10.1002/adma.201802379, 30, 34, 182379.
