(Lecture, Oct 22) Device Operation and Stability of Polymer Light-emitting Diodes


Title: Device Operation and Stability of Polymer Light-emitting Diodes
Speaker: Prof.Paul W.M Blom (Max Planck Institute for Polymer Research)
Venue: Room 501, Building No.1, Wushan Campus
Time: Oct. 22, Monday, 14:30-16:00
Device operation and stability of polymer light-emitting diodes
Paul W.M. Blom
Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz, Germany
The transport of electrons in conjugated polymers is strongly reduced by traps that are Gaussianly distributed in energy in the band gap. Remarkably, the electron trap distribution is identical for a large number of organic semiconductors. This universal defect also quenches the excitons in conjugated polymers. We have found that by blending poly(p-phenylene vinylene) (PPV) derivatives with wide band gap polymers the electron traps are deactivated. PLEDs made from such a blend exhibit a balanced transport and enhanced efficiency due to the strong reduction of non-radiative trap-assisted recombination. The limited stability of PLEDs under current stress impedes commercialization. The voltage drift of a PLED driven at constant current is caused by the formation of hole traps, which initially increases linearly with time (burn-in) and subsequently grows with the square-root of time. This transition is governed by the statistics between free and trapped holes. The mechanism for the efficiency decrease under stress, is the additional non-radiative recombination between free electrons and trapped holes. The observed trap formation rate is consistent with exciton-free hole interactions as the main mechanism behind PLED degradation.
Paul W.M. Blom was born in Maastricht , The Netherlands, in 1965. Hereceived his Ir. Degree (Physics) in 1988 and his Ph. D. Degree in 1992, respectively, from the Technical University Eindhoven, Eindhoven, The Netherlands. His thesis work was on picosecond charge carrier dynamics in GaAs quantum wells. At Philips Research Laboratories he was engaged in the electrical characterization of various oxidic thin-film devices, the electro-optical properties of polymer light-emitting diodes and the field of rewritable optical storage based on phase-change and magneto-optical recording using blue laser diodes. In May 2000 he was appointed as a Professor at the University of Groningen, where he was heading a group in the field of electrical and optical properties of organic semiconducting devices. The main research focus was on the device physics of polymeric light-emitting diodes, transistors, solar cells and memories. In September 2008 he was appointed as the Scientific Director of the Holst Centre in Eindhoven where the focus is on the realization of electronic systems in foil. Since September 2012 he joined the Max Planck Institute for Polymer Research in Mainz as director in the field of molecular electronics. The main research directions are organic electronics, ferroelectric polymers and bio-electronics. He co-authored over 300 papers in these research fields (h-index 81).

Announced by School of Matreials Science and Engineering