Charge transport and recombination in heterostructure organic light emitting transistors

• Solution processed hetero-structure light emitting transistors (LEFETs) were fabricated.
• Charge transport and photo physics of LEFETs were studied as a function of temperature.
• Higher external quantum efficiency (EQE) was achieved as the system cooled down.
• Established that the higher EQE at lower temperature is primarily due to an increased radiative recombination process.

Light-emitting field effect transistors (LEFETs) are a class of organic optoelectronic device capable of simultaneously delivering the electrical switching characteristics of a transistor and the light emission of a diode. We report on the temperature dependence of the charge transport and emissive properties in a model organic heterostructure LEFET system from 300 K to 135 K. We study parameters such as carrier mobility, brightness, and external quantum efficiency (EQE), and observe clear thermally activated behaviour for transport and injection. Overall, the EQE increases with decreasing temperature and conversely the brightness decreases. These contrary effects can be explained by a higher recombination efficiency occurring at lower temperatures, and this insight delivers new knowledge concerning the optimisation of both the transport and emissive properties in LEFETs.

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