Simultaneous Optimization of Light Gain and Charge Transport in Ambipolar Light-Emitting Polymer Field-Effect Transistors

Ambipolar light-emitting field-effect transistors (LEFETs) based on poly(9,9-dioctylfluorene- alt -benzothiadiazole) (F8BT) are able to combine electrical switching capability with the generation of light within a well-defined recombination zone inside the channel. Therefore, they are an attractive architecture not only for low-loss light signal transmission in optoelectronic integrated circuits but also for the potential realization of electrically pumped organic lasers. However, these applications require a simultaneous optimization of transistor performance and waveguiding of emitted light. Here we show that to achieve efficient waveguiding and optical gain the annealing temperature of the F8BT film has to be kept at 120 °C below its glass transition temperature. At such low processing temperatures it is difficult to achieve efficient ambipolar charge injection from gold source/drain electrodes and charge transport at the active transistor interface. We show that modification of the gold electrodes with a 1-decanethiol self-assembled monolayer (SAM) allows efficient charge injection into F8BT films deposited on top. The performance of such ambipolar LEFETs with SAM-modified electrodes is better than that of devices with bare gold electrodes but processed at higher temperatures.