Inhaltszusammenfassung

This work puts forth a study of the exciton diffusion properties in conjugated polymers with respect to the following questions: How does the energetic disorder in conjugated polymers influences exciton diffusion characteristics such as the exciton lifetime, exciton diffusion coefficient, exciton diffusion length, and photoluminescence quantum yield in a solid thin film? How does the exciton diffusion depend on temperature with respect to various degree of energetic disorder? Is it possible t...This work puts forth a study of the exciton diffusion properties in conjugated polymers with respect to the following questions: How does the energetic disorder in conjugated polymers influences exciton diffusion characteristics such as the exciton lifetime, exciton diffusion coefficient, exciton diffusion length, and photoluminescence quantum yield in a solid thin film? How does the exciton diffusion depend on temperature with respect to various degree of energetic disorder? Is it possible to minimize exciton quenching at non-radiative quenching-sites by optimization of the polymer synthesis or film processing conditions? The goal of this work is to understand on one hand the interplay between the energetic disorder of the conjugated polymer and the device performance, and on the other hand the factors, which limit the exciton diffusion characteristics in a conjugated polymer film. Chapter 3 demonstrates that the exciton lifetime and photoluminescence quantum yield (PLQY) directly correlates with the energetic disorder of the conjugated polymer, where increased energetic disorder slows down the diffusion of the exciton toward non-radiative quenching sites and strongly enhances both exciton lifetime and PLQY. This is consistent with diffusion-limited exciton quenching at non-radiative recombination centers in organic semiconductors. In Chapter 4, time-resolved photoluminescence (TRPL) spectroscopy at varying temperature show a correlation between the energetic disorder and the balance between radiative and non-radiative decay processes, the latter of which includes also non-radiative decay processes due to exciton diffusion toward excitonic traps. We found distinct temperature dependencies of the exciton diffusion properties based on the polymer disorder, which also determines the polymer light-emitting diode (PLED) performance. TRPL spectroscopy is further used to investigate the PL decay in degraded PLED (Chapter 5), that was aged at a constant current density, leading to the formation of hole traps. The TRPL demonstrates a decrease in exciton lifetime in the degraded PLED device with respect to the unaged one. The amount of non-radiative exciton quenching-sites in the aged device is quantified by Monte Carlo simulations, which is found to match with the number of hole traps predicted from electrical charge transport measurements. Our results reveal the origin for the apparent different behavior of the electroluminescence and photoluminescence upon PLED degradation. The decrease of the electroluminescence is governed by recombination of free electrons with trapped holes, whereas the photoluminescence is reduced by non-radiative quenching processes between excitons and hole traps.» weiterlesen» einklappen

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DDC Sachgruppe:
Naturwissenschaften