Cathodoluminescence characterization of organic semiconductor materials for light emitting device applications

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Abstract
We report the development of a cathodoluminescence-based characterization technique for the investigation of organic semiconductormaterials for organic light emitting device (OLED) applications. While photoluminescence is known to predominantly address singlet exciton excitation and recombination processes, cathodoluminescence is able to simultaneously probe singlet and triplet exciton dynamics which is of importance for electroluminescence. Especially, in the case of the so-called triplet harvester materials, the generation of triplet excitons during cathodoluminescence opens the way for materials characterization without device fabrication. The paper (i) shows how cathodoluminescence can be applied for the characterization of organic semiconductormaterials, (ii) points out the general measurement factors, (iii) discusses the special features of cathodoluminescence, electroluminescence as well as photoluminescence spectra, and (iv) outlines the potential of cathodoluminescence by presenting a brief study of a triplet harvester material systems. Main emphasis is put on the presentation of the characterization tool to partly replace the necessity of OLED fabrication. For that reason widely used conjugated polymers and small molecule semiconductor systems have been selected.