Molecular Tailoring of New Thieno(bis)imide-Based Semiconductors for Single Layer Ambipolar Light Emitting Transistors

Abstract

Organic molecular semiconductors are key components for a new generation of low cost, flexible, and large area electronic devices. In particular, ambipolar semiconductors endowed with electroluminescent properties have the potential to enable a photonic field-effect technology platform, whose key building blocks are the emerging organic light-emitting transistor (OLET) devices. To this aim, the design of innovative molecular configurations combining effective electrical and optical properties in the solid state is highly desirable. Here, we investigate the effect of the insertion of a thieno(bis)imide (TBI) moiety as end group in highly performing unipolar oligothiophene semiconductors on the packing, electrical, and optoelectronic properties of the resulting materials. We show that, regardless of the HOMO–LUMO energy, orbital distribution, and molecular packing pattern, a TBI end moiety switches unipolar and nonemissive oligothiophene semiconductors to ambipolar and electroluminescent materials. Remarkably, the newly developed materials enabled the fabrication of single layer molecular ambipolar OLETs with optical power comparable to that of the equivalent polymeric single layer devices.

Organic Light‐Emitting Transistors: Materials, Device Configurations, and Operations

“…In addition to initiating new ambipolar OSCs from scratch, a slight modification of existing OSCs is another efficient way to obtain emerging materials of ambipolar transistor performance. A relevant instance was reported by Melucci and co‐workers, where a thieno(bis)imide (TBI) moiety as end group was inserted in high‐performance unipolar oligothiophene to promote ambipolar charge transport and EL . It is widely acknowledged that the introduction of an electron‐donating moiety to π‐conjugated molecules could generally favor the production of OSCs of hole transport capability, while an electron‐withdrawing moiety facilitates electron transport .…”

“…Remarkably, these newly developed materials have enabled the fabrication of single layer ambipolar OLETs with optical power comparable to that of the equivalent polymeric single layer devices. It was believed that these results opened the perspective of enabling high power emitting devices exploiting the high mobility values typical of small molecules …”

“…In fact, in addition to three‐terminal OLETs, light‐generation functionalities can also be absolutely realized via conventional two‐terminal OLEDs, where most of the merits of OLETs can be harnessed in nearly the same way. Nevertheless, for the technological application of OLEDs, especially when they work as the component of active‐matrix EL display panels, field‐effect transistors are always essentially required to control their EL behavior and to switch each individual OLED pixel ON or OFF in terms of controlling the current density . The circuits in these cases are generally constructed by complicated and high‐cost fabrication techniques.…”

“…In contrast, no supplementary devices are required when OLETs are employed for similar uses, owing to the merger of light‐generation and electrical switching functionalities in a single device architecture. From the standpoint of practical applications, OLETs accordingly pave a promising avenue towards highly integrated optoelectronics, which could be manufactured by easy and low‐cost processes due to the largely reduced number of switching transistors and circuit complexity …”

Active channel field-effect transistors: Towards high performance light emitting transistors

“…Both evaporated [49][50][51][52][53] and solution processed [2,42,[54][55][56] organic semiconductors have been used as emissive layers. There are also LEFETs based on carbon nanotubes [57,58], however these devices emitted light in the infrared and were not useful for display or lighting applications.…”