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In this investigation, it is showed for the first time that a piezoelectric poly-(l-lactic acid) (PLLA) unimorph based cantilever device is utilized in energy harvesting applications. The cantilever device comprises of double layer of PLLA and a thick layer of polyethylene terephthalate substrate as a passive layer. Under the optimized conditions, the output power of the PLLA cantilever devices can reach a maximum value of 14.17 µW, and an open circuit voltage of 9.05 V. The generated signal can be rectified through a full-bridge circuit and used to charge a lithium-ion battery to 3.2 V within 7.5 h. The charged battery can successfully light up 30 light-emitting diodes for two minutes. Furthermore, after the PLLA film was thermally treated at 140 °C for 24 h, the material still shows a shear mode piezoelectric coefficient d 14 of 9.57 pC N−1. The cantilever device fabricated from a double layer of thermally treated PLLA film can still generate an output voltage of 9.4 V and a slightly higher power output of 14.45 µW. This observation indicates that the PLLA material can be used to replace piezoelectric polymers with a lower Curie temperature in self-powered devices under high temperature conditions.