Direct electrostatic toner marking with poly(3,4-ethylenedioxythiophene)polystyrenesulfonate bilayer devices

Abstract

Poly(3,4-ethylenedioxythiophene)polystyrenesulfonate (PEDOT:PSS) is the one of the most promising and widely used materials for low cost large area flexible displays, owing to its easy solution processing and micro/nano scale patternability. In this work, hole injection between PEDOT:PSS thin film and molecularly doped polymer layers of arylamine has been studied in a bilayer device configuration. The electrical properties of the bilayer devices have been examined by studying their charge-discharge behavior, current-voltage (I-V), and time-of-flight (TOF) characteristics. The work function of the PEDOT:PSS and arylamine has been estimated by electrochemical measurements. Results show that PEDOT:PSS is an efficient hole injector to arylamine owing to its favorable molecular energetics. The efficiency of hole injection depends on the conductivity of the PEDOT:PSS film and the strength of the electric field across the bilayer device. The interfacial electrical contact behavior between PEDOT and arylamine studied by steady state I-V measurements and TOF measurements suggests that for highly conductive PEDOT:PSS, the discharge of the bilayer device is limited by the hole mobility in the charge transport layer whereas it is injection limited for more resistive PEDOT:PSS films. Printing experiments were performed on a modified xerographic DC12 printer as well as a modified DC8000 development housing. The overall results show that the latent image produced by discharging the bilayer device can be developed electrostatically with toner. More importantly, we found that the PEDOT:PSS bilayer device can be charged, discharged, and developed by just loading it against a negatively biased magnetic toner brush. We suggest coupling this direct toner marking process with an active backplane for digital printing application. The proposed digital printer appears to be very simple and compact as printing can be done without using a charger and the laser ROS system and replacing the photoreceptor with the PEDOT bilayer device that is controlled by an active backplane. The operating bias estimated for the Thin Film Transistors (TFTs) in the backplane is about −200 V. We believe that the bias voltage can be further reduced by using a thinner charge transport layer and by optimizing the toner development process. Although the bias voltage is still high, it is within reach for today's high-voltage TFT technology.