Fixed p-i-n junction polymer light-emitting electrochemical cells based on charged self-assembled monolayers

The authors report on enhanced efficiency of polymer light-emitting electrochemical cells (LECs) by means of forming a $n$ -doping self-assembled monolayer (SAM) at the cathode-polymer interface. The addition of the SAM, a silane-based salt with structural similarity to the commonly used LEC $n$ -dopant tetra-$n$ -butylammonium, caused a twofold increase in quantum efficiency. Photovoltaic analysis indicates that the SAM increases both the open-circuit voltage and short-circuit current. Current versus voltage data are presented which indicate that the SAM does not simply introduce an interfacial dipole layer, but rather provides a fixed doping region, and thus a more stable $p\text{-}i\text{-}n$ structure.