ENERGY TRANSFER AND CHARGE TRAPPING PROCESSES IN POLY(N-VINYLCARBAZOLE) DOPED WITH IRIDIUM COMPLEXES
I. Glowacki, Z. Szamel
Department of Molecular Physics, Technical University of Lodz, 90-924 Lodz, Zeromskiego 116, Poland (Ireneusz.Glowacki@p.lodz.pl,
Polymer light-emitting diodes (PLEDs) have attracted great attention because polymeric materials are the most promising candidates for future flexible panel displays. By employing phosphorescent dyes, such as iridium complexes, the internal quantum efficiency of the PLEDs can be very high (high atomic number metals enhance spin-orbit couplingleading to relatively short triplet lifetimes) with emission tuneable from red to blue.
Charge trapping and radiative recombinationare fundamental processes influencing the efficiency of the electroluminescent devices. One of the most direct methods of investigation of the charge carriers trapping, detrapping and radiative recombination is thermoluminescence (TL).
In this study several iridium complexes were doped to poly(N-vinylcarbazole) (PVK). The TL measurements were carried out for the doped polymer films in the temperature range 15-325 K. The TL curves were registered with simultaneous spectral analysis of the emitted light.
Each of the investigated dyes results in different changes of the TL spectrum in comparison to the neat PVK film. The TL results indicate an effective energy transfer from the PVK matrix to the dyes. The charge trapping occurs on both the matrix and the dopants. In doped PVK density of deeper traps considerably increases.
This work was financed in some part from polish grant MNiI 3TO8E01327 and NoE Nanofun-Poly UE contract No. NMP3-CT-2004-500361.