4.4 Using additives
Additive treatment is an effective means to optimize the morphology.
This method is to add a small amount of additives which are quite
different from the properties of the main solvent into the solution, and
to control the morphology of the active layer by changing the state of
the solution and film-forming kinetics.[24, 114] The introduction of
additives can generally reduce solvent volatilization rate, prolong
film-forming time and enhance
crystallinity. At the same time, additives generally have selective
solubility, which can adjust the precipitation sequence of molecules and
effectively adjust the phase separation structure.[115] In addition,
adding solid additives can inhibit the further phase separation and
improve the stability.[116]