Top publications

Elimination of Charge Carrier Trapping

Electron Trapping in Conjugated Polymers

Efficient Blue Polymer Light‐Emitting Diodes

Exiton Quenching at PEDOT:PSS Anode

Elimination of charge carrier trapping in diluted semiconductors

In 1962, Mark and Helfrich demonstrated that the current in a semiconductor containing traps is reduced by N/N t r, with N the amount of transport sites, N t the amount of traps and r a number that depends on the trap energy distribution. For r> 1, the possibility opens that trapping effects can be nearly eliminated when N and N t are simultaneously reduced. Solution-processed conjugated polymers are an excellent model system to test this hypothesis, because they can be easily diluted by blending them with a high-bandgap semiconductor. We demonstrate that in conjugated polymer blends with 10% active semiconductor and 90% high-bandgap host, the typical strong electron trapping can be effectively eliminated. As a result we were able to fabricate polymer light-emitting diodes with balanced electron and hole transport and reduced non-radiative trap-assisted recombination, leading to a doubling of their ...

Author: D Abbaszadeh, Alexander Kunz, GAH Wetzelaer, Jasper J Michels, NI Crăciun, Kaloian Koynov, Ingo Lieberwirth, Paul WM Blom
Publication date: 2016

Exciton quenching at PEDOT: PSS anode in polymer blue-light-emitting diodes

The quenching of excitons at the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) anode in blue polyalkoxyspirobifluorene-arylamine polymer light-emitting diodes is investigated. Due to the combination of a higher electron mobility and the presence of electron traps, the recombination zone shifts from the cathode to the anode with increasing voltage. The exciton quenching at the anode at higher voltages leads to an efficiency roll-off. The voltage dependence of the luminous efficiency is reproduced by a drift-diffusion model under the condition that quenching of excitons at the PEDOT:PSS anode and metallic cathode is of equal strength. Experimentally, the efficiency roll-off at high voltages due to anode quenching is eliminated by the use of an electron-blocking layer between the anode and the light-emitting polymer.

Author: D Abbaszadeh, GAH Wetzelaer, Herman T Nicolai, Paul WM Blom
Publication date: 2014

Efficient Blue Polymer Light‐Emitting Diodes with Electron‐Dominated Transport Due to Trap Dilution

As is common for many conjugated polymers used in light‐emitting diodes (PLEDs), the charge transport in blue‐emitting polyspirobifluorene (PSF) copolymerized with the hole transport unit – N,N,N′N′‐tetraaryldiamino (TAD) biphenyl – is dominated by holes. Although the free electron mobility is an order of magnitude higher than the hole mobility, the electron transport is strongly hindered by traps. By diluting PSF‐TAD with the wide band gap polymer poly(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl) (PFO), the effect of electron trapping can be nearly eliminated. As a result, the transport in the PSF‐TAD:PFO blend becomes electron dominated. Due to the higher electron mobility, PLEDs made from these blends exhibit higher current and light‐output as compared to hole‐dominated PLEDs made from pristine PSF‐TAD. The reduced amount of electron traps enhances their efficiency from 2 cd A−1 for the hole‐dominated …

Author: Davood Abbaszadeh, Paul WM Blom
Publication date: 2016

Who we are?!

The Device-Physics of Electronic Materials (D-POEM) group is the experimental condensed matter branch of the Physics Department at the IASBS. We study electron transport in organic and hybrid organic-inorganic nanostructured materials using experimental methods. Beside this, to deploy the physics of these materials we try to model the obtained measured results numerically. We aim to work on the state-of-the-art topics and materials that are used to make the new types of photovoltaics, light-emitting diodes, memristors, thermoelectrics, etc. For this, we have made several collaborations with some very prestigious groups in Iran and outside of Iran. Want to join? Contact us!