18
Light-Emitting Organic Crystal Field-Effect Transistors for Future Organic Injection Lasers
18.1 Introduction
Organic semiconductor-based light-emitting devices such as organic light-emitting diodes (OLEDs) and light-emitting organic field-effect transistors (LE-OFETs) have demonstrated the tremendous potential of organic semiconducting materials. In OLEDs, a maximum external quantum efficiency (ηext) of 20%, corresponding to an internal quantum efficiency (ηint) of nearly 100%, has been achieved through the use of phosphorescent emissive materials such as Ir complexes [1, 2]. However, unipolar, ambipolar, or static induction transistor-type LE-OFETs have been produced by careful selection of organic semiconductors and optimization of device fabrication procedures [3]. Although light-emitting organic semiconductors possess excellent light amplification characteristics [4–7] and existing OLEDs and LE-OFETs exhibit exceptional light-emitting performance, challenges still remain in the field of organic light-emitting devices such as the development of organic injection lasers.
To realize an organic injection laser, the principal requirements are (i) injection and transport of very high current density in organic semiconductors, (ii) suppression of exciton annihilation, and (iii) minimization of waveguide loss by the electrodes. Previous results and problems preventing the realization of organic injection lasers include the following:
