Synergistic photothermoelectric energy conversion in core-shell polydopamine coated upconversion nanoparticles

Artificial light harvesters (ALHs) are being developed for emerging energy conversion technologies, such as photothermoelectric (PTE) that convert photon energy into electricity via a secondary step of heat (thermal) production utilizing the Seebeck effect. The reported ALH uses erbium-doped NaGdF4 upconversion nanoparticles (UCNPs) that are excited at 980 nm coated with a broadband absorber polydopamine (PD) shell (UCNP@PD). The photothermal efficiency of the UCNP@PD was synergistically enhanced to 67% compared to 13% and 44% obtained for pure UCNPs and a physical mixture of UCNP + PD under 980 nm illumination. The ALHs were then coated on commercial thermoelectric generator (TEG) modules and studied under 980 and 808 nm lasers and a white desktop lamp. The PTE output (voltage/current) of the UCNP@PD-coated TEG module could produce 100.2 mV/22.1 mA under 980 nm irradiance. In comparison, UCNP and PD individually showed PTE output of 39.5 mV/9.7 mA and 69.8 mV/16.2 mA, respectively, proving the synergy in UCNP@PD attributed to the re-absorption of the UCNP emission in the PD shell. Under low-power white light illumination, the UCNP@PD-coated TEG module can result in 19.9 mV/4.52 mA PTE output.