Influence of Topology on Performance of Organic Electrochemical Transistor

Abstract

Organic electrochemical transistors (OECTs) with two topologies and three ionic liquid electrolytes were analyzed to get information about their influence on the selected transistor's characteristics. The channel of the OECT device was based on conductive polymer poly (3,4-ethylenedioxy- Keywords Organic Electrochemical Transistor (OECT), Ionic liquid (IL), PEDOT:PSS, OECT structure, printed electronics, screen printing IntroductionOne of the key device of organic electronics for simple electronic circuits is an organic field effect transistor (OFET) which is widely studied from the point of view of both theoretical and practical aspects [1][2][3]. OFETs typically operate at voltages in the order of tens of volts and lot of efforts was spent to decrease the operating voltage below 10 V.In contrast to OFETs, the organic electrochemical transistor (OECT) exhibits some advantageous properties, such as very low operating voltage [4], ability to work in the liquid environment [5], and simple fabrication process using common printing methods such as inkjet [6] and screen printing [7][8][9][10]. However, OECT exhibits also some disadvantages. The main one being low switching performance in terms of the switching speed and the switching ratio, which are crucial for some type of applications. The switching performance is directly proportional to the speed and efficiency of the electrochemical redox reaction in the channel between the polymer semiconductor backbone and ions injected from the gate electrode. Note that unlike OFET, the gate electrode being formed from the electrolyte is in direct contact with the channel between source and drain electrodes in the OECT. In our study we used for the channel of OECT most commonly used p-type organic polymer poly(3,4-ethylene dioxythiophene) -poly(styrene sulfonate) (PEDOT:PSS). This polymer exhibits a variety of advantageous properties such as environmental stability, good film-forming ability and the possibility to vary its electric conductivity by several orders of magnitude [11].After the application of electric field between the gate and source (drain) electrode the ions (free to move) are injected into the channel and the electrochemical reaction starts. According to Eq. (1) cations M + are injected. Thus, PEDOT + (holes) and cations are present in the redox reaction. PEDOT + is reduced and comes into neutral "non-conducting" PEDOT 0 state at the side of negative electric potential. Charge carrier concentration decreases and transistor is in the OFF state.