Highly Efficient OLEDs

12Photophysics of Thermally Activated Delayed Fluorescence

Andrew Monkman

University of Durham, OEM Research Group, Department of Physics, South Road, Durham, DH1 3LE, England

12.1 Introduction

One of the major successes of OLED research has been the discovery of methods to overcome the limitation imposed by charge recombination spin statistics [1]. As we know, upon charge recombination three times more triplet excited states are generated than singlet states; therefore the maximum internal efficiency (IQE) of an OLED is limited to 25% [2], unless methods to “harvest” the triplets, i.e. convert them to emissive singlet states, are used. Saying this, in many fluorescent OLEDs, the 25% limit is exceeded by the “accidental” use of triplet fusion ...