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OLED Display Fundamentals and Applications by Takatoshi Tsujimura

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2

OLED Display Structure

2.1 OLED DEFINITION

Before any in-depth discussion of OLED display structure, let us consider the initial origins of OLED technology, which are based on early observations of electroluminescence. In the early 1950s, a group of investigators at Nancy University in France applied high-voltage alternating-current (AC) fields in air to acridine orange and quinacrine, which were dissolved in or deposited on thin-film cellulose or cellophane [1]. One mechanism identified in these processes involved excitation of electrons. Then in 1960 a team of investigators at New York University (NYU) made ohmic dark-injecting electrode contacts to organic crystals and described the necessary workfunctions (energy requirements) for hole and electron-injecting electrode contacts [2]. These contacts are the source of charge injection in all present-day OLED devices. The same NYU group also studied direct-current (DC) electroluminescence (EL) in vacuo on a single pure anthracene crystal and tetracene-doped anthracene crystals in the presence of a small-area silver electrode at 400 V [3]. The proposed mechanism for this reaction was termed field-accelerated electron excitation of molecular fluorescence. The NYU group later observed that in the absence of an external electric field, the EL in anthracene crystals results from recombination of electron and hole, and that the conducting-level energy of anthracene is higher than the exciton energy level [4].

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