15

Device Efficiency of Organic Light-Emitting Diodes

Wolfgang Brütting and Jörg Frischeisen

15.1 Introduction

The availability of artificial light has been a seminal cultural development of mankind. After open fires for thousands of years, the introduction of electricity together with the invention of the light bulb in the second half of the nineteenth century has revolutionized our daily life. Having dominated the lighting market for more than 100 years, however, the light bulb faces its decline due to the need for technologies that convert electricity more efficiently into visible light. Besides fluorescent lamps, which are already well established in the market, the availability and progress in white light-emitting diodes, both inorganic and organic, over the last decade has led to a new lighting technology called solid-state lighting [1]. Its working principle, namely, the radiative recombination of injected electron–hole pairs in a solid, a process termed electroluminescence, is fundamentally different from thus far existing techniques and holds the promise for highly efficient, long-lived, and environment-friendly light sources. In contrast to their inorganic counterparts, organic light-emitting diodes (OLEDs) are flat and thin large-area light sources that could rather lead to complementary luminaires than competitors to existing technologies.

Historically speaking, electroluminescence in organic molecular crystals dates back to the early 1960s [2, 3], however, the important ...

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