Multifunctional Flexible Device Based on Phosphor on Piezoelectric Polymer: Lighting, Speaking, and Pressure-Light Converting

In this paper, the tri-functional flexible device by using ZnS powder as phosphor layer and flexible piezoelectric polymer as dielectric layer is demonstrated. The fabricated device generates the electroluminescent (EL) light from the phosphor and the sound from the piezoelectric sheet under a supply of external electric power, and additionally harvests the mechanical energy harvesting to be converted into EL light. Under sinusoidal applied voltage, the EL luminances are exponentially increased, to our best knowledge, with the best-record luminous efficiency of 10 lmW(-1) at 100V and 400 Hz, and the sound pressure levels (SPLs) are linearly increased. The EL luminances are linearly dependent on the applied frequency while the SPLs show the parabolic increase behavior below 2000 Hz and then flat response. The temperature dependence on the EL luminances and the SPLs is demonstrated; the former is drastically increased and the latter is slightly decreased with the increase of temperature. Finally, as an energy harvesting application, the piezoelectric electroluminescence effect is demonstrated by applying the external pressure on the device without electric power. This trifunctional device is expected to be applicable to emergency warning system, advertising panel, and remote stress sensor in both power-on and -off circumstances.