Name : Tal Elbaz Ph.D. student. Supervisor: Prof. Rafi Shikler Subject: Using the Critical Point Model of the Dielectric Function to Correlate Morphology and Opto-Electronic Properties of Organic-Based Devices

Abstract Organic semiconductors are central to modern electronic and optoelectronic devices. While thin-film morphology critically governs charge transport and device performance, common deposition methods provide limited morphological control, necessitating sensitive characterization techniques to elucidate the physical properties. We demonstrate that spectroscopic ellipsometry (SE) combined with Critical Point (CP) analysis enables rapid, non-destructive assessment of microstructural evolution during thermal annealing. The CP model provides physically meaningful optical parameters that exhibit strong correlations with electrical performance. Using P3HT-based organic thin-film transistors as a benchmark system and extending the approach to other polymers and device architectures, our results reveal a clear annealing-induced dimensionality shift in the optical transition, indicating increased crystallinity and reduced energetic disorder. These optically derived descriptors accurately predict improvements in charge-carrier mobility, establishing SE–CP analysis as a practical tool for early-stage materials evaluation and process optimization.