Self-absorption effects in a LEC with low Stokes shift

The electroluminescence spectra both in forward and reverse directions of a light-emitting electrochemical cell prepared from a methyl-substituted ladder-type poly(paraphenylene) (mLPPP), blended with a crown ether, Dicyclohexano18crown6 (DCH18C6), and a Li salt, lithium trifluoromethanesulfonate (litriflate, LiTf for short) are compared. Different from the forward direction, in reverse direction the spectrum is strongly influenced by self-absorption effects. We discuss this behavior by different degrees of doping of the p- and n-type doped zones. This effect can be applied for a new method to realize bias-dependent color emission from single-layer devices at low voltages that can be prepared by only one simple and easy spin-coating process.