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Various light output measures of red/near-infrared (NIR) excimer-based organic light-emitting diodes (LEDs) are reported for different cathodes (Al, Al∕LiF, Ca, and Ca∕PbO2). By using a selected phosphor (PtL2Cl) from a series of terdentate cyclometallated efficient phosphorescent Pt(II) complexes, PtLnCl, as the neat film emitting layer and a Ca∕Pb(IV)O2 cathode, the authors achieve unusually high forward viewing external quantum efficiencies of up to 14.5% photons/electron and a power conversion efficiency of up to 6% at a high emission forward output of 25mW∕cm2. These are the highest efficiencies reported for a NIR organic LED. Electron tunneling through thin insulating layers of LiF and Pb(IV)O2 and the difference in band bending at the organic electron transporting layer and the cathode between the samples are used to explain this performance achievement.
Cocchi et al. (Mon,) studied this question.