“…Before post-heating, the sample was predominantly coated with the DMF layer, and then P[VDF-TrFE] nanoparticles (NPs) were not observed.After post-heating at 160 • C for 3 h, the deposited film had a smooth surface with P[VDF-TrFE] NPs, as shown in Figure6b. Moreover, the FE-SEM measurement confirmed a small amount of bubble particles due to DMF solvent attached to the P[VDF-TrFE] thin film.In general, in the case of increasing a film thickness, piezoelectric polymer film can improve an electrical property, such as dielectric strength and energy density, especially in a piezoelectric nanogenerator[34], whereas, for the optical properties of PVDF-TrFE film, the optical transmission of PVDF-TrFE film is reported to be reduced due to a loss of light, thus resulting in increasing the refractive index with an increase in the film thickness[35]. It will be necessary to carry out further study on effects of the film thickness change through both…”