Electro-to-thermal conversion testing of PVDF-PW@PPy composite films. (a) Electrical conductivity of the composite film at different polymerisation times. (b) Voltage-current (V-I) curve of the composite film. (c) Temperature of the composite film at different test voltages. (d) Principle of the electro-to-thermal conversion test and a representative infrared thermal image captured at 10 min after applying a voltage of 2.5 V. (e) Images of composite film illuminating a bulb or driving a small fan within a closed circuit. (f) Temperature curve of the composite film during long-time testing. (g) Temperature curve of the composite film during seven continuous tests at 2.5 V.