Chemical doping to control the in-situ formed doping structure in light-emitting electrochemical cells

The initial operation of a light-emitting electrochemical cell (LEC) constitutes the in-situ formation of a p–n junction doping structure in the active material by electrochemical doping. It has been firmly established that the spatial position of the emissive p–n junction in the interelectrode gap has a profound influence on the LEC performance because of exciton quenching and microcavity effects. Hence, practical strategies for a control of the position of the p–n junction in LEC devices are highly desired. Here, we introduce a “chemical pre-doping” approach for the rational shifting of the p–n junction for improved performance. Specifically, we demonstrate, by combined experiments and simulations, that the addition of a strong chemical reductant termed “reduced benzyl viologen” to a common active-material ink during LEC fabrication results in a filling of deep electron traps and an associated shifting of the emissive p–n junction from the center of the active material towards the positive anode. We finally demonstrate that this chemical pre-doping approach can improve the emission efficiency and stability of a common LEC device.