Resolving the Spin Coating Process via In Situ Transmission Measurements

Abstract

Spin coating is one of the most common techniques for the production of thin films in laboratories. In this work, we investigate spin coating of a P3HT/PC71BM blend while in situ measuring the change in transmission to gain a general understanding of the film-forming-process. We show that spin coating can be divided into three phases: first, the distribution phase; second, a film thinning phase; and finally, film crystallization. The final morphology of the crystalline film at the end of the spin coating process is almost entirely influenced by the crystallization phase, whereas the other phases do not have the same influence on the final film quality. We found that processing conditions, such as decreasing the solution temperature, decreasing the spin speed, or increasing the solution concentration, increase the crystallinity of the film. This is always related to an increase in crystallization phase duration. When using additives in the solution, such as 1,8-diiodooctane, we observe a similar behavior in the timing of the crystallization phase.