Wireless Electroluminescence: Polymer Light-Emitting Electrochemical Cells with Inkjet-Printed 1D and 2D Bipolar Electrode Arrays

Abstract

One-dimensional (1D) and two-dimensional (2D) arrays of conductive microdisks are printed on glass substrates using a silver nanoparticle (Ag-NP)-based ink. Polymer light-emitting electrochemical cells (PLECs) are then fabricated on top via spin-coating and the thermal deposition of aluminum driving electrodes (DEs). The extremely large planar PLECs, with an interelectrode separation of 11 mm, are driven with a bias voltage of 400 V. This causes in situ electrochemical doping in the polymer from both DEs and the Ag-NP disks. The latter functions as bipolar electrodes (BPEs) to induce and sustain doping reactions at their extremities. Time-lapse photoluminescence and electroluminescence (EL) imaging reveals that p- and n-doping originating from neighboring BPEs can interact to form multiple light-emitting p–n junctions, connected in series by the BPEs. Unexpectedly, the multiple p–n junctions begin to emit well before a continuous pathway of doped polymers is established between the DEs. This observation breaks one of the general rules of PLEC emission. The EL is therefore wireless in the sense that the emitting junctions are not directly addressed by the DEs. The doping patterns confirm that the 1D vertical arrays of BPE disks can function like a single rod-shaped BPE when individual BPE disks are connected in a series by the light-emitting p–n junctions. Doping induced by an 8 × 8 2D BPE array showed that the electric field in the PLEC film was initially highly uniform but quickly became distorted by the strong doping from the BPE disks. Intense (visible to the naked eye) junction EL is observed from the 56 light-emitting p–n junctions formed. The demonstration of functional inkjet-printed BPEs and their applications to PLECs allows for easy generation of BPE patterns to probe the complex doping processes in PLECs.