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Organic crystals that combine high charge-carrier mobility and excellent light-emission characteristics are expected to be of interest for light-emitting transistors and diodes, and may offer renewed hope for electrically pumped laser action. High-luminescence-efficiency cyano-substituted oligo(p- phenylene vinylene) (CN-DPDSB) crystals (η ≈ 95%) grown by the physical vapor transport method is reported here, with high mobilities (at ≈10−2 cm2 V−1 s−1 order of magnitude) as measured by time-of-flight. The CN-DPDSB crystals have well-balanced bipolar carrier-transport characteristics (μhole≈ 2.5–5.5 × 10−2 cm2 V−1 s−1; μelectron ≈ 0.9–1.3 × 10−2 cm2 V−1 s−1) and excellent optically pumped laser properties. The threshold for amplified spontaneous emission (ASE) is about 4.6 μJ per pulse (23 KW cm−2), while the gain coefficient at the peak wavelength of ASE and the loss coefficient caused by scattering are ≈35 and ≈1.7 cm−1, respectively. This indicates that CN-DPDSB crystals are promising candidates for organic laser diodes.

It has recently been suggested that the charge recombination rate in amorphous polymers could be affected by the energy distribution of electrons and holes as well as that of the resulting excitons. To test this hypothesis, we developed a new method for measuring charge recombination under highly imbalanced conditions. We find that if the electron density is higher than that of the holes, increasing the electron density further results in reduction of the recombination coefficient. We attribute this to the very different energy distribution between low and high carrier densities, which is not accounted for in the Langevin recombination model.