• Forrest, S. R.
• Baldo, M. A.

Abstract

<p>We examine the effects of nonradiative losses on lasing in crystalline and amorphous organic thin films. In crystalline films, the dominant loss mechanism is singlet-singlet annihilation, and this must be avoided if lasing is to be achieved at practical current densities. The electrically pumped crystalline-tetracene laser structure of Schön et al. [Science 289, 599 (2000)] is studied in detail. Optical and electrical confinement in the bulk structure appears unable to explain the spectral narrowing reported; consequently, we consider electron-hole plasmas, self-focusing at interfaces, and crystal defects as possible sources of the reported phenomena. In amorphous films, lasers are likely to have to operate at current densities J &lt; 1000 A/cm² due to a combination of nonradiative losses. The performance of potential lasing materials is quantified by the external quantum efficiency-current-density product, η_EXTJ. Electrically pumped lasers require η_EXTJ∼5 A/cm²; the best amorphous devices currently posses η_EXTJ∼0.3 A/cm². However, we demonstrate that electrically pumped lasing in amorphous materials should be possible using indirect pumping techniques.</p>

Topics

• density
• impedance spectroscopy
• amorphous
• thin film
• defect