π-Conjugated metallo-copolymer/SWCNT composites for high performance thermoelectric generators

Organic materials have attracted extensive attention in flexible thermoelectric generators due to their solution processability, low thermal conductivity and high flexibility. However, their thermoelectric performances are still far behind those of the inorganic counterparts (e.g. Bi₂Te₃, PbTe and other related alloys). Here, by virtue of the dual advantages of both inorganic and organic materials, three Pt (II)-containing diketopyrrolopyrrole (DPP) based donor−acceptor (D−A)-type π-conjugated metallo-copolymers (P1Pt, P2Pt and P3Pt) are designed and synthesized, and they are compared with their control copolymers without Pt (II)-coordination (P1, P2 and P3). It is shown that Pt (II) centers and copolymerized molecular structures play important roles in tuning the bandgap and coplanarity. A large Fermi level shift is observed after doping with single-walled carbon nanotubes (SWCNTs) in the copolymers. As expected, the introduction of Pt (II)-side chains and doping of SWCNTs into copolymers could significantly improve the power factor (PF), which reaches the highest value of 276.5 ± 26.6 μW m⁻¹ K⁻² for P3Pt/60 wt% SWCNTs. The corresponding p-type thermoelectric generator exhibits a large output power of up to 0.55 μW under a 109 K temperature gradient. Our results can provide a pathway for designing and preparing efficient thermoelectric materials and flexible thermoelectric generators.