High-resolution imaging of electrochemical doping and dedoping processes in luminescent conjugated polymers

We report fluorescence imaging of extremely large planar polymer light-emitting electrochemical cells (LECs) with high spatial and temporal resolution. The type of cation used has been shown to strongly affect $n$ -doping propagation. When left to relax, $p$ doping undergoes significantly faster relaxation than $n$ doping. Imaging also confirms that a $p\text{-}n$ junction, rather than a $p\text{-}i\text{-}n$ junction, is formed in fully turned on LECs, which suffer from heavy photoluminescence quenching throughout the polymer film. However, a $p\text{-}i\text{-}n$ junction with a much less quenched “intrinsic” region can be formed by relaxing a $p\text{-}n$ junction without bias, suggesting a simple approach for achieving more efficient LECs.