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In conventional light-emitting electrochemical cells (LECs), an off-centered p–n junction is one of the major drawbacks, as it leads to exciton quenching at one of the charge-injecting electrodes and results in performance instability. To combat this problem, we have developed a new device configuration, the double-gate light-emitting electrochemical transistor (DG-LECT), in which the location of the light-emitting p–n junction can be precisely defined via the position of the two gate terminals. Based on a planar LEC structure, two gate electrodes made from an electrochemically active conducting polymer are employed to predefine the p- and n-doped area of the light-emitting polymer. Thus, a p–n junction is formed in between the p-doped and n-doped regions. We demonstrate a homogeneous and centered p–n junction as well as other predefined junction patterns in these DG-LECT devices. Additionally, we report an electrical model that explains the operation of the DG-LECTs. The DG-LECT device provides a new tool to study the fundamental physics of LECs, as it dissects the key working process of LEC into decoupled p-doping, n-doping, and electroluminescence. [ABSTRACT FROM AUTHOR]

Low-voltage-operating organic electrochemical light-emitting cells (LECs) and transistors (OECTs) can be realized in robust device architectures, thus enabling easy manufacturing of light sources using printing tools. In an LEC, the p-n junction, located within the organic semiconductor channel, constitutes the active light-emitting element. It is established and fixated through electrochemical p- and n-doping, which are governed by charge injection from the anode and cathode, respectively. In an OECT, the electrochemical doping level along the organic semiconducting channel is controlled via the gate electrode. Here we report the merger of these two devices: the light-emitting electrochemical transistor, in which the location of the emitting p-n junction and the current level between the anode and cathode are modulated via a gate electrode. Light emission occurs at 4 V, and the emission zone can be repeatedly moved back and forth within an interelectrode gap of 500 μm by application of a 4 V gate bias. In transistor operation, the estimated on/off ratio ranges from 10 to 100 with a gate threshold voltage of -2.3 V and transconductance value between 1.4 and 3 μS. This device structure opens for new experiments tunable light sources and LECs with added electronic functionality. [ABSTRACT FROM AUTHOR]