White-colour electroluminescence from porous-silicon diodes capped with organic conductive adduct

Organic charge-transfer conductive adducts of tetrathiafulvalene (TTF) and bis (ethylenedithio) tetrathiafulvalene (ET) are proposed as materials for top electrical contacts in porous-silicon-based light-emitting devices. Semitransparent conductive adduct coatings were produced by impregnating PSi layers with a solution containing the desired adduct. Improvement in brightness (2.5×10³ fold) and luminous efficiency (10⁴ fold) have been achieved. Devices made with top contacts of TTF(NO₃)_0.55 and ET (NO₃)_0.67 emit white light whereas those made with TTFI_0.71 and TTF(SCN)_0.45 emit yellow light. Internal luminous efficiency of 1.41 mW^-1 has been obtained for ET(NO₃)_0.67-capped devices. The carrier injection was found to obey a space-charge-limited current model