Kinetically arresting surface-directed phase separation in vapor-deposited glasses

Well-controlled phase separation in organic films is required for stable, tunable organic semiconductor devices; however, competing thermodynamic and kinetic effects during solution deposition can lead to unpredictable structure and stability changes, along with non-uniform phase separation throughout the film depth. To address these issues, we use physical vapor deposition (PVD) to isolate kinetic effects and prepare thin films of an organic semiconductor blend with finely tunable phase separation. By changing the deposition rate, and therefore the rate of kinetic arrest of liquid-liquid phase separation, we find that the length scales of phase separation in the deposited film depend smoothly on deposition rate. Complementary AFM and resonant soft X-ray scattering (RSoXS) measurements suggest that the phase separation is uniform throughout the depth of the film. By combining processing and metrology, we can move towards precise design of materials for more efficient, longer-lasting organic electronics.