Active Layer Of Light-emitting Diodes Research Articles

Influence of silicon atoms on the ?-conjugation in electroluminescent polymers

By means of the valence effective Hamiltonian (VEH) method, we calculated the electronic structure for a polymer containing poly(para-phenylene vinylene) (PPV) and dimethoxy-poly(para-phenylene) (PPP) units as well as silicon atoms used as spacers. The equilibrium geometry was obtained by an AM1 calculation. We obtained a band gap of 3.2 eV, which corresponds to emittance in the blue part of the spectrum. This polymer is used as the active layer in light-emitting diodes. © 1997 John Wiley & Sons, Inc.

Electroluminescence of regioregular poly(alkylthiophenes)

Regioregular poly(4,4′-didecyl-2,2′-bithiophene) with exclusively head-to-head and tail-to-tail couplings between adjacent alkylated thiophene rings was studied as a potential material for the active layer in light-emitting diodes (LEDs). Readily visible green light was derived from a single layer LED structure. The electroluminescence (EL) spectrum peaks at 2.2 eV. Excitation of photoluminescence (PL) resulted in green light with the spectrum peaked at 2.3 eV. Additionally to the electroluminescence and photoluminescence measurements, the absorption spectrum is reported. Determination of the optical energy gap gave Eg equal to 2.9 eV. The same experiments performed for another regioregular polyalkylthiophene system (with only head-to-tail couplings) showed extremely poor EL and PL intensity, below the sensitivity of our spectrometer. The difference in yield of photo- and electroluminescence is likely interpreted in terms of trapping of excitons in conjugated blocks separated by head-to-head dyads, where they decay. Non-planarity of the polymer backbone also influences the relative positions of singlet and triplet states.

Poly( p-phenylene vinylene) as active layer in light-emitting diodes: a theoretical investigation of the effects of derivatization

In this work, we investigate the way the geometric, electronic and optical properties of para-phenylene vinylene oligomers are affected upon derivatization, either by introducing π-donor and/or π-acceptor substituents along the chain or by incorporating nitrogen atoms within the conjugated backbone. We show that the results of our quantum-chemical calculations are relevant in the context of the use of the corresponding polymers in light-emitting diodes.

Influence of donor and acceptor substituents on the electronic characteristics of poly(paraphenylene vinylene) and poly(paraphenylene)

We investigate theoretically the influence of substitution by various donor and acceptor groups onto the phenyl rings and/or the vinylene units of poly(paraphenylene vinylene) and poly(paraphenylene). Using quantum chemical methods, we calculate the magnitudes of the forbidden energy gaps, the ionization potentials, and the electron affinities for several derivatives of each of the two parent conjugated polymers. These electronic parameters are essential in determining the potential of such polymers for use as active layers in light-emitting diodes.

Optoelectronic Device Physics Based on Conjugated Polymers

Abstract We have developed means for processing conjugated polymers to allow fabrication of a variety of semiconductor device structures. These polymers include polyacetylene prepared via the Durham precursor route and various poly(arylene vinylenes) prepared via sulphonium precursor polymers. We have shown that these devices exhibit novel electro-optical properties which depend for their operation on the non-linear character of the electronic excitations of the polymer chain. We discuss here the use of poly(phenylene vinylene) and derivatives as the active layers in light-emitting diodes.