The project made substantial progress in developing and applying advanced optical techniques to investigate charge trapping phenomena in organic field-effect transistors (OFETs). The core aim—to enable spatially resolved identification and characterization of charge traps using laser-based optical probing—was addressed through a structured programme of experimental and instrumentation work, encompassing optical system development, material optimization, and device fabrication.
A major achievement of the project was the successful design, construction, and commissioning of a custom optical setup for charge trap mapping. The system incorporates high-precision translation stages, microscope optics, and a multi-wavelength laser source, all integrated via custom-built mechanical components and software for automated control and data acquisition. This setup enabled localized optical excitation of OFETs with spatial resolution sufficient to detect position-dependent electrical responses, marking a significant step forward in the study of localized trapping phenomena.
Many OFET devices were fabricated using various organic semiconductor (OSC) materials and geometries. Among the tested materials, TMTES-pentacene, particularly when blended with polystyrene, exhibited the most robust and stable photoresponse. This material was ultimately selected as the model system for systematic studies. A reproducible device architecture was established, enabling consistent measurements of photoinduced effects under controlled conditions.
The optical studies revealed a rich and reproducible photoresponse localized near the source electrode of the OFETs. These effects were found to be persistent and dependent on the wavelength and dose of light exposure, consistent with the presence of long-lived trapped charge carriers. These observations provided new insight into minority carrier trapping mechanisms and their influence on OFET performance, and form the basis of an upcoming scientific publication.
In parallel, progress was made in understanding how fabrication parameters influence the photoresponse and trap characteristics of OFET devices. Systematic testing of different OSCs, blend ratios, and deposition techniques facilitated optimization of device structures suitable for optical probing. While some fabrication degrees of freedom were constrained by the need for high spatial resolution, critical insights into material selection and device stability were obtained.
In support of future work on electrolyte-gated OFETs (EG-OFETs), a novel electrical measurement geometry was developed and successfully integrated into the optical setup environment. Although full optical characterization of EG-OFETs was not conducted within the reporting period, the preparatory work, including the design and fabrication of a spring-loaded contact system, lays the foundation for subsequent optical studies on these complex devices.
In summary, the project successfully delivered a fully functional and highly specialized optical probing setup, demonstrated its applicability to OFET devices through extensive experimental measurements, and identified materials and fabrication protocols enabling reproducible studies of charge traps.
