Pyroelectric energy harvesting using Olsen cycles in purified and porous poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] thin films

This paper is concerned with the direct conversion of heat into electricity using pyroelectric materials. The Olsen (or Ericsson) cycle was experimentally performed on three different types of 60/40 poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer samples, namely commercial, purified, and porous films. This cycle consists of two isoelectric field and two isothermal processes. The commercial and purified films were about 50 mu m thick and produced a maximum energy density of 521 J l(-1) and 426 J l(-1) per cycle, respectively. This was achieved by successively dipping the films in cold and hot silicone oil baths at 25 and 110 degrees C under low and high applied electric fields of about 200 and 500 kV cm(-1), respectively. The 11 mu m thick porous films achieved a maximum energy density of 188 J l(-1) per cycle between 25 and 100 degrees C and electric field between 200 and 400 kV cm(-1). The performance of the purified and porous films suffered from their lower electrical resistivity and electric breakdown compared with commercial thin films. However, the energy densities of all 60/40 P(VDF-TrFE) films considered matched or exceeded those reported recently for 0.9Pb(Mg1/3Nb2/3)O-3-0.10PbTiO(3) (0.9PMN-0.1PT) (186 J l(-1)) and Pb(Zn1/3Nb2/3)(0.955)Ti0.045O3 (243 J l(-1)) bulk ceramics. Furthermore, the results are discussed in light of recently proposed figures of merit for energy harvesting applications.