Near-infrared polymer light-emitting diodes based on low-energy gap oligomers copolymerized into a high-gap polymer host.

Near-infrared (NIR) polymer light-emitting diodes (PLEDs) based on a fluorene-dioctyloxyphenylene wide-gap host material copolymerized with a low-gap emitter are presented. Various loadings (1, 2.5, 10, 20 mol%) of the low-gap emitter are studied, with higher loadings leading to decreased efficiencies likely due to aggregation effects. While the 10 mol% loading resulted in almost pure NIR emission (>99.6%), the 1 mol% loading yielded optimum device performance, which is among the best reported to date for a unblended single-layer pure polymer emitter, with an external quantum efficiencies of 0.04% emitting at 909 nm. The high spectral purity of the PLEDs combined with their performance support the methodology of copolymerization as an effective strategy for developing NIR PLEDs. Polymer light-emitting diodes are fabricated by copolymerizing a low-bandgap donor-acceptor-donor segment in various loadings with a high-gap fluorene dialkoxybenzene host. By controlling the loadings, emission wavelength and efficiency could be controlled, resulting in an emission at ≈909 nm with an external quantum efficiency of almost 0.04%, which is one of the best at this wavelength for a single-layer pure polymer emitter.