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Physics of Organic Semiconductors, 2nd, Completely New Revised Edition by Russell J. Holmes, Chihaya Adachi, Wolfgang Brutting

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12

Recent Progress in the Understanding of Exciton Dynamics within Phosphorescent OLEDs

Sebastian Reineke and Marc A. Baldo

12.1 Introduction

Phosphorescence is now widely adopted in commercial organic light-emitting devices (OLEDs). It has reached its position as the premier high-efficiency technology after a long development effort. Despite this, many of the underlying mechanisms remain unclear, attracting continuing research interest and the attention of regular scientific reviews [1–3]. Here, we focus on recent developments in three areas of particular relevance to the operation of phosphorescent OLEDs. Following the lifecycle of the excited states, we first review advances in the understanding of exciton formation, with a particular focus on emerging competitors to phosphorescence. Then, we review progress in the understanding and control of exciton transport and harvesting, before concluding with a summary of present knowledge about exciton quenching.

12.2 Exciton Formation

12.2.1 Background

In an OLED, the conversion of electrical energy into light is mediated by excitons. It is the properties of the excitons that primarily determine the overall luminescent efficiency of the device.

An exciton may be thought of as a two-electron system: one electron is excited into a previously unfilled orbital of a given molecule or polymer, while the second remains in a partially filled ground state. The partially filled ground state is often known as a hole, and imagined to possess a ...

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