Ambipolar organic light emitting transistors employing heterojunctions of n-type and p-typematerials as the active layer

The realization of organic light-emitting transistors (OLETs) with high quantum efficiency and fast switching time is crucial for the development of highly integrated organic optoelectronic systems. In order to reach such a goal, fabrication of devices with ambipolar transport and high charge mobility values is needed. At present, organic materials having intrinsically ambipolar transport are restricted in number and show poor performance. This limits their use in efficient and fast switching single layer ambipolar OLETs. In this framework, we have taken the approach of combining p-type and n-type materials in two complementary configurations. The first one is based on realizing layered structures (bi-layer heterojunction) where materials are sequentially deposited. The second one is based on simultaneously evaporating two materials with variable composition ( bulk heterojunction) to form a mixed film. In this paper, the charge transport and electroluminescence properties of OLETs based on these heterostructures are presented. A correlation between the active layer structure and the electrical performances has been obtained by means of laser scanning confocal microscopy, here employed for morphology and spectroscopy analysis. Differences between the two approaches are critically discussed.