Ionic thermoelectrics show great potential in thermal sensing owing to their ultrahigh thermopower, low cost, and ease in production. However, the lack of effective n-type ionic thermoelectric materials seriously hinders their applications. Here, we report giant and bidirectionally tunable thermopowers within an ultrawide range from −15 to +17 mV K −1 in solid ionic liquid-based ionogels. Particularly, a record high negative thermopower of −15 mV K −1 is achieved in the ternary ionogel, rendering it among the best n-type ionic thermoelectric materials under the same condition. A thermopower regulation strategy through ion doping to selectively induce ion aggregates to enhance ion-ion interactions is proposed. These selective ion interactions are found to be decisive in modulating the sign and magnitude of the thermopower in the ionogels. A prototype wearable device integrated with 12 p-n pairs is demonstrated with a total thermopower of 0.358 V K −1 , showing promise for ultrasensitive thermal detection.
centuries, it was only recently that noontime cooling was first demonstrated using a multilayer photonic structure. [2] In tropical and subtropical areas, the demand for cooling is particularly huge due to high ambient temperatures. However, it is proved that daytime cooling is difficult to achieve in such areas with stronger solar irradiation and higher humidity than mid-latitude regions. [3][4][5][6][7] With the increase in humidity, the transmittances within the atmospheric windows remarkably decrease, while most secondary windows such as the 16-25 µm window may even disappear in humid climates (Figure S1, Supporting Information). This significantly increases the atmospheric radiation and limits the cooling capability of radiative coolers, especially those with strong IR absorption/emission beyond the major atmospheric window. Although broadband IR emitters may provide ≈10% higher cooling power potential than selective ones in less humid climates due to the existence of secondary windows, in humid areas with high precipitable water vapor (PWV), this advantage vanishes and their cooling temperatures are notably limited by broadband IR absorption. [8] To maintain applicability in different climates, an ideal daytime radiative cooler should show high emittance only within the main Daytime radiative cooling provides an eco-friendly solution to space cooling with zero energy consumption. Despite significant advances, most state-ofthe-art radiative coolers show broadband infrared emission with low spectral selectivity, which limits their cooling temperatures, especially in hot humid regions. Here, an all-inorganic narrowband emitter comprising a solutionderived SiO x N y layer sandwiched between a reflective substrate and a selfassembly monolayer of SiO 2 microspheres is reported. It shows a high and diffusive solar reflectance (96.4%) and strong infrared-selective emittance (94.6%) with superior spectral selectivity (1.46). Remarkable subambient cooling of up to 5 °C in autumn and 2.5 °C in summer are achieved under high humidity without any solar shading or convection cover at noontime in a subtropical coastal city, Hong Kong. Owing to the all-inorganic hydrophobic structure, the emitter shows outstanding resistance to ultraviolet and water in long-term durability tests. The scalable-solution-based fabrication renders this stable high-performance emitter promising for large-scale deployment in various climates.
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