Description of the thesis topic

Organic electronics offer a promising alternative to inorganic electronics for large-area applications, particularly in displays and flexible sensors. Among these devices, Organic Thin-Film Transistors (OTFTs) provide advantages in terms of low-cost fabrication and compatibility with flexible substrates. However, their commercial integration remains limited due to insufficient performance and stability issues, particularly in ambient conditions and over long periods. The Organic And Silicon System team of IETR (Institute of Electronic and Telecommunications of RENNES, France; https://www.ietr.fr/) aims to take part of this fascinating topic promoting a disruptive technology (1 patent pending technology). One of the major technological bottlenecks is the high contact resistance at the source and drain (S&D) electrodes, which negatively impacts charge injection efficiency and carrier mobility. These resistances, influenced by interface trap states and charge injection barriers, hinder device performance and long-term reliability. While various contact engineering strategies have been explored, further innovation is needed to enable the widespread adoption of OTFTs in commercial applications.
PhD Objectives: This PhD project aims to develop new strategies for improving S&D contacts in OTFTs, reducing contact resistance, and enhancing device stability. Two complementary approaches will be investigated:
1. Replacing heterojunction contacts with homojunctions The objective is to optimize charge injection by using an intrinsic polymer semiconductor (OIPSC), locally doped to create a conductive zone (ODPSC) acting as the electrode. This approach is expected to minimize energy discontinuities at the interfaces and reduce interface trap density.
2. Implementation of a transfer printing process for S&D electrode fabrication This method, linked to a patent filed in 2024 (FR2412688), aims to adapt materials and manufacturing processes to demonstrate the effectiveness of transfer printing in producing printed OTFTs. This technique is designed to optimize electrode topology and reduce access resistance.

Work Context

This PhD project builds on the expertise of the OASiS department at IETR in inkjet-printed OTFT fabrication and is part of the ANR-funded SMOOTH (Stable Metal-free Organic transistOrs Thanks to Homojunction) project, which will start in February 2025 and run for four years. The project involves multiple partners:
• OTFT characterizations : L2n-URCA Reims (O. Simonetti)
• Polymer synthesis: ICPEES Strasbourg (N. Leclerc)
• Material deposition: ICS Strasbourg (M. Brinkmann)
• Ink formulation and printing process optimization: IETR Rennes (Maxime Harnois, Emanuel Jacques and Fabien LUCAS)
The research will focus on:
• Formulating and optimizing dopant inks for printed conductive regions,
• Investigating doping mechanisms and their stability,
• Electrical and morphological characterization of transistors,
• Evaluating device stability under real-world operating conditions.

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.

Constraints and risks

cleanroom working