Fig. 3: The design and characterization of the upper layer.
a Schematic of the cross-section of the upper layer, from top to bottom, including a Fresnel lens, an air layer separated by a transparent quartz plate with antireflection coatings, PT layer on the top of a TE generator. The entire PTE converter is enclosed by a polymethyl methacrylate shell. b The estimation of convective heat transfer coefficient in the presence of an air layer with different d between PT layer and Fresnel lens, or under NIR-II light irradiation with different LPDs. c The investigation of the effect of the separator inserted in the air layer with different d, by recording Δt0 relative to body temperature (37 °C) under NIR-II irradiation with LPD of 0.3 W cm−2 for 10 min. d The predicted temperature distribution on the Fresnel lens which is the top surface of the PTE converter under NIR-II irradiation with LPD of 0.3 W cm−2 for 10 min via finite element analysis. The top images are assigned to the upper layer without or with a quartz separator, respectively. e The transmittance of PMMA (raw materials of Fresnel lens and protective shell), the quartz separator, and the quartz separator with antireflective coatings in VIS–NIR window. The thickness of each sample is 1.0 mm. Inset: the image of Bio-PS. f The time-dependent open circuit voltage of the bare PTE converter and packaged PTE converter having an upper layer under NIR-II light irradiation with LPD of 0.3 W cm−2. g Open circuit voltage generated by PTE converter with an upper layer under NIR-II light irradiation with different LPDs.
