Enhancement of Output Power in Self-Assembled Electret-Based Vibrational Energy Generator: Control of Molecular Orientation by Changing Deposition Rate

Recently, we developed self-assembled electret (SAE)-based vibrational energy generator (VEG) which can generate electrical power from ambient vibrations. An advantage of the device is that any charging process is not required for making electret, that is, surface potential (V
sp
) of SAE naturally appears only by vacuum deposition. This is because the V
sp
originates from spontaneous orientation of polar molecules such as Alq
3
and TPBi. Thus, to increase output power of SAE-VEG, enhancement of order parameter of the molecule, $\langle \cos \theta \rangle$, is required. In this study, we prepared TPBi-based SAE films with various deposition rate (r
dep
). We found that the V
sp
becomes 1.8 times larger in the case of high r
dep
of 4.0 Å/s, suggesting that molecular orientation can be controlled by r
dep
. This result indicates that further enhancement of output power in SAE-VEG can be realized through optimization of fabrication process of SAE.