Impact of Intermittent Deposition on Spontaneous Orientation Polarization of Organic Amorphous Films Revealed by Rotary Kelvin Probe

The control of the molecular orientation and resultant polarization is essential for improving the performance of organic optoelectronic devices. Conventionally, the substrate temperature and deposition rate are tuned to control the molecular orientation of vapor-deposited films. In this study, we proposed a novel method, referred to as "intermittent deposition", in which the polarization direction and magnitude are controlled by introducing intervals during physical vapor deposition. The rotary Kelvin probe measurement of the Alq₃ and TPBi films clearly showed a time-dependent decrease in the surface potential owing to the surface relaxation of the molecular orientation immediately after deposition. Through a series of intermittent depositions, in which the deposition shutter is repeatedly opened and closed at certain intervals, a relaxed surface layer was built up, and we could control the polarization magnitude. For the Alq₃ film, even the polarization direction was switched. The proposed new deposition method is applicable to general organic molecules, not limited to polar molecules, thereby potentially tuning the conduction properties of organic devices and fabricating novel devices.