  We demonstrate exciton and charged exciton (trion) electroluminescence from
frozen p-n junctions in networks of polymer-sorted, semiconducting (6,5)
single-walled carbon nanotubes. Electrolyte-gating with an ionic liquid was
employed to achieve injection and accumulation of high densities of holes and
electrons in the nanotube network at low applied voltages. Static p-n junctions
were formed by cooling the devices below the melting point of the ionic liquid
while in the ambipolar regime. These frozen junctions showed diode-like
rectification and enabled the investigation of electron-hole recombination and
near-infrared electroluminescence under controlled conditions. The
contributions of exciton and red-shifted trion emission to the
electroluminescence spectra were influenced by the initial parameters of the
p-n junction formation (balanced or unbalanced) and the applied lateral bias,
but did not depend on temperature (30-200 K). The tilted potential profile
along the fixed junction and consequently the number of excess carriers within
the recombination zone were found to predominantly determine the emission
intensity and observed trion to exciton ratio.
