Probing The Microscopic Origins of Device Performance and Stability in Organic Semiconductors through Trap Density of States Spectroscopy

Organic semiconductors (OSCs) are highly susceptible to defect formation, owing to their weak intermolecular interactions, leading to trap states in the band gap that can drastically alter their optoelectronic properties. Characterization techniques that can elucidate the mechanisms of defect formation and evolution are essential for guiding the processing and design of high-performance stable OSC devices. In this presentation I will discuss a highly efficient methodology to elucidate the microscopic processes occurring within the OSC when deliberately exposed to different external stimuli. The methodology relies on real-time access to the trap density of states (t-DOS) spectrum of the OSC using organic field-effect transistor (OFET) measurements. The t-DOS spectrum provides detailed information about the origin and energetic distribution of electronic traps in OSCs, as well as their time evolution. Several different trap states will be discussed as case studies, including those arising from impurities and isomer coexistence, microstrain at device interfaces, environmental and bias stress. Methods for minimizing the trap density to enhance performance and stability will be presented. Finally, the exploitation of trap formation for the development of radiation dosimeters for cancer treatment will be discussed.