Real-time monitoring of drop-casting growth of TIPS-pentacene films by <i>in situ</i> differential reflectance spectroscopy

In situ and real-time monitoring reveals the dynamic reactions, changes, and even unexpected constructions occurring during the growth process, which is crucial for understanding the fundamental growth mechanism and control of film quality. The solution-based growth approach is widely applied for organic semiconductors because of its easy implementation, low costs, and large-scale growth, whereas its in situ monitoring is yet less studied. Here, we developed a fast differential reflectance spectroscopy (DRS) system for real-time monitoring of drop-casting growth of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene). The results demonstrate that the extremely low-drift DRS could successfully capture the growth process of TIPS-pentacene thin film, including the ultrafast solvent evaporation, transient liquid-solid transition, and eventually formation of the TIPS-pentacene film. A four-phase optical model was developed to fit the in situ collected DRS spectra, which revealed the dynamic changes in the volume fraction of TIPS-pentacene solution and the effective thickness of TIPS-pentacene film. This work demonstrates an effective approach to in situ monitoring of physical and even chemical reactions at the liquid-solid interface.