Direct measurement of the singlet generation yield in polymer light-emitting diodes.

In this study, the singlet and triplet exciton generation yields of a representative blue-emitting conjugated polymer are directly compared using simultaneous optical and electrical excitation measurements. After carefully accounting for bimolecular triplet annihilation and knowing the independently measured solid state inter-system-crossing yield of the polymer, a singlet generation yield of 44% is obtained, in the working device, which is clearly in excess of the simple quantum statistical 25% limit.