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We present the optical and electronic properties of a polymeric semiconductor, a new soluble stable ladder-type poly(para-phenylene) (LPPP, band gap=2.69 eV) and demonstrate its excellent applicability in blue-green electroluminescence (EL) devices. The high intrachain order and the low defect concentration of the polymer lead to a remarkably low absorption coefficient in the subgap region (αmin12 cm−1 at 1.5 eV) and also to a high photoluminescence quantum efficiency (30% in the solid state). The current/electric field characteristics of the high efficiency (up to 0.04 photons/electron) EL devices reveal a polymer film thickness dependence on the required onset field due to ordering effects in the active polymer layer. The shape of the recorded EL spectra can be controlled by the applied electric field in the blue-green spectral range.
Tasch et al. (1996) studied this question.