Solution-processed semiconductor colloidal quantum dots (CQDs) gradually attract attentions as low-cost, printing-compatible materials for flexible systems. They have been employed for optoelectronics for their tunable absorption spectrum and narrow emission linewidth brought by quantum size-effect. The amorphous nature of CQD thin-films also enables them to be mass-produced on lightweight, flexible plastic substrates using reel-to-reel printing, spray painting and ink-jet printing. Till now, CQDs have been widely used in solar energy harvesting, logic devices and displays. However, CQDs haven’t been widely used on strain and pressure sensing systems, since CQDs lack proper transduction mechanisms (i.e. piezoelectric, piezoresistive) to respond to strain or pressure.
Here we report a novel application of quantum dots – introducing triboelectric phenomenon into CQD devices to create a CQD triboelectric field-effect transistor (TFET) for high-performance flexible touch sensors. In our touch sensors, we use a polydimethylsiloxane (PDMS) film to generate triboelectric voltage in response to touching and a floating-gate CQD FET to produce source-drain current modulated by the triboelectric voltage. This design makes it possible to generate a much larger current change compared to the free-standing PDMS touch sensor. The fabrication process of CQD TFET doesn’t require expensive equipment (reactive ion etching etc.) which enables the potential of our devices to be mass produced by printing technologies at low cost in industry. We further improve the performance of our TFET touch sensors by the surface modification strategy. This strategy will largely enhance the mobility of CQD solid, thereby increase the current output of CQD TFET touch sensors.