Flexible organic ferroelectric films with a large piezoelectric response

Compared with ferroelectric oxides, organic ferroelectric materials are lightweight, flexible and easy to process. They are ideal for applications in the next-generation portable electronics. Here, we demonstrate the room-temperature growth of imidazolium perchlorate (C3N2H5ClO4) ferroelectric films on various substrates, including Pt-coated Si, quartz and, more importantly, on flexible and transparent polyethylene terephthalate (PET). The films have a preferred (0 - 1 - 1) or (10 - 1) orientation. The former shows a piezoelectric response comparable with the response of the Pb(Zr0.2Ti0.8)O-3 film. This is attributed to the smaller elastic constant of the film, which makes it less susceptible to substrate clamping. When grown on PET, the film is transparent and can be bent to radii of a few millimetres without affecting its ferroelectric properties. Our discovery may significantly promote the application of molecular ferroelectrics in flexible and transparent electronics.