Abstract
AbstractThe charge transport and recombination in light‐emitting diodes (LEDs) based on a methyl‐substituted poly(p‐phenylene) ladder polymer (Me‐LPPP) are investigated. The transport is characterized by a high room‐temperature hole mobility of 2 × 10−8 m2 V−1 s−1 combined with anomalously strong electron trapping. Their electroluminescence (EL) spectrum is characterized by a blue singlet emission, a broad green featureless peak, and a yellow‐orange triplet emission. The voltage dependence of the EL spectrum and negative contribution to the capacitance indicate that the triplet‐emission is of trap‐assisted nature, consistent with the strong electron trapping. Consequently, the color purity of the blue emissive Me‐LPPP polymer LEDs can be strongly improved using trap dilution.
Highlights
Of conjugated polymers due to their are investigated
Single-Carrier Devices Understanding the operation of PLEDs requires a thorough characterization of charge transport, charge injection, and recombination mechanisms
The hole transport in Me-LPPP is characterized by a trap-free space-charge limited current with a high mobility of 2 × 10−8 m2 V−1 s−1 due to reduced energetic disorder
Summary
To model the trap-free hole current, the extended Gaussian disorder model (EGDM) was used that contains as relevant parameters μ0, a mobility prefactor containing the electronic overlap between transport sites, the energetic disorder σ, and a, the average distance between two transport sites.[21,22] These parameters define the dependence of mobility on temperature, charge carrier density, and electric field. Me-LPPP device, the hole- and electron current differ by nearly five orders of magnitude Such a large difference is ten to hundred times larger than observed for other PPV derivatives[23,24]. Me-LPPP could point to the fact that next to these universal traps additional trap centers are present in the band gap of Me-LPPP
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