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Study of Organic Field Effect Transistors: Realization of Ambipolar OFETs and Study of Injection Mechanisms in Vertical OFETs

by Laurence Laffont - published on , updated on

Marjorie MORVAN’s thesis defense intitled "Étude des transistors à effet de champ organiques : Réalisation d’OFETs ambipolaires et étude des mécanismes d’injection dans les OFETs verticaux" (Study of Organic Field Effect Transistors: Realization of Ambipolar OFETs and Study of Injection Mechanisms in Vertical OFETs) will be taking place on Wednesay, December 16th 2020 at 2 pm by visioconférence.

The work has been supervized by par Mr Georges ZISSIS, Mr David BUSO and Mr Marc TERNISIEN.

Link to the visioconférence:

Subject : Soutenance Thèse Marjorie Morvan
Time : dec. 16 2020 01:50 PM Paris
Participate in the Zoom meeting :
Meeting ID : 863 2577 7800

Please mind your microphones and cameras.

Jury :

Mr Kamal LMIMOUNI - University of Lille 1 - Rapporteur
Mr Christian LEGRAND - University of Littoral Côte d’Opale - Rapporteur
Ms Geneviève DUCHAMP - University of Bordeaux - Reviewer
Mr Georges ZISSIS - University Toulouse III Paul Sabatier - LAPLACE Laboratory - Thesis Supervisor
Mr David BUSO - University Toulouse III Paul Sabatier - LAPLACE Laboratory - Thesis co-Supervisor
Mr Marc TERNISIEN - University Toulouse III Paul Sabatier - LAPLACE - Thesis co-Supervisor

Abstract :

Organic Field Effect Transistors (OFETs) have gotten increasingly attractive thanks to the possibility of producing lighter components at lower cost and on flexible substrates. Being able to couple a light emission function to a transistor function makes its use more interesting. This is the case with display applications, where the pixels are produced by an active matrix technology of organic light-emitting diodes (AMOLED). Having a light-emitting OFET makes it possible to combine an OFET with an organic light-emitting diode (OLED) and hence simplify the design, the manufacturing steps as well as the increasing of pixels’ lifetime.

During this thesis, the studying and manufacturing of light-emitting OFETs were carried out using two approaches. The first one was based on the study of ambipolar OFETs using N, N’-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13), an n-type semiconductor, and pentacene, a p-type semiconductor. This study established the first step in obtaining electroluminescent OFETs. The fabrication and characterization of these ambipolar OFETs were performed for the first time by the LAPLACE laboratory’s research team. A study of their structure was carried out to find the ideal parameters to obtain a balanced charge transportation. The optimized structure was a bilayer structure with a pentacene thickness of 8 nm and a PTCDI-C13 thickness of 20 nm. The addition of an emitting layer between the two semiconductors failed to achieve light emission due to excessive charge trappings. However, this study has opened up new perspectives for future work on ambipolar OFETs.

The second approach to study light-emitting OFETs is more innovative thanks to a structural change from a classic planar structure to a vertical one. This structure has the advantage of being able to easily integrate an OLED structure and has a homogeneous light emission over a large area. The operating principle is totally different from conventional OFETs: here, the power modulation is no longer done by controlling the conductivity in a semiconductor channel, but by controlling the injection of charges at the source electrode. The study of this structure made it possible to obtain luminous organic transistors. Then, the study of charge injection mechanisms allowed us to understand more deeply the operating principe of these transistors. Several materials have been tested as source electrodes: gold, silver, aluminum and ITO (Indium Tin Oxide). This study helped to determine the injection mechanism involved, namely the injection of charges by the modulation of the tunnel effect thanks to the band-bending induced by the gate effect in the semiconductor layer close to the interface. It has also been identified that the quality of the source electrode/semiconductor interface played a major role since poor interface quality lead to a drastic decrease in performance.

Keywords :
Organic electronics, OFETs, Vertical Organic Transistors, OLED