Real-time monitoring of trap dynamics reveals the electronic states that limit charge transport in crystalline organic semiconductors

Abstract

Organic semiconductors (OSCs) have the potential to become ubiquitous in our lives as part of various optoelectronic devices given their low-cost processing, light weight, and the opportunities that they offer for designing new materials with “on demand” properties. Many OSCs have achieved remarkable performances, however, a complete understanding of the fundamental processes that govern their properties is still lacking. One such process is charge carrier trapping, a phenomenon that profoundly impacts the performance and stability of devices. Here we report on a comprehensive study on the physics of traps resulting from microstructure changes by monitoring the generation/annihilation of traps in 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES ADT), a high-mobility small molecule OSC. The variations in charge carrier mobility measured in organic field-effect transistors (OFETs) deliberately exposed to solvent vapor are correlated with the density and energetic distribution of the electronic states in the band gap of the OSC in all intermediate states of the microstructural transformations. Given the strong dependence of the electrical properties on the film microstructure, such information is instrumental in identifying performance-limiting processes in devices and subsequently guiding material processing to achieve intrinsic limits. The discovery of defect-tolerant intermediate crystalline motifs may provide new pathways for fabricating stable, high-performance devices for next-generation low-cost electronics.