Solar-driven evaporation is a promising technology with many potential applications including desalination, power generation, purification, sterilization, and phase separation. Recently, much research has been directed toward increasing solar-driven evaporation efficiencies with photothermal materials that reside at the air−water interface to provide a localized thermal energy source when subjected to solar radiation. In this work, composite foams of carbon nanoparticles (CNPs) and polydimethylsiloxane (PDMS) were fabricated by a facile salt-leaching technique and used as interfacial receivers for solar evaporation. The inclusion of CNPs significantly increases the solar absorptivity of the foams to ∼97% without impacting their inherently low thermal conductivity. Polyvinyl alcohol (PVA) modification was applied to endow the foams with hydrophilicity, thereby enabling continuous water transport to the air−water interface. An enhanced water evaporation rate of 1.26 kg/m 2 •h with a solar-to-evaporation efficiency of 80% was achieved under a relatively low solar input of 850 W/m 2 . With their simple structure and excellent photothermal performance, the PVA-CNP/PDMS foams are promising candidates for solar evaporation applications.

The usage of ultrathin flexible silicon foil can further extend the functionality of silicon and emerging silicon-based tandem solar cells particularly in building and vehicle-integrated photovoltaics where high-efficiency, lightweight, and flexible solar panels are highly desired. However, silicon's relatively weak optical absorption coefficient especially in the near infrared (NIR) region limits its optoelectronic applications with a reduced wafer thickness. Herein, we seek to overcome this limitation by exploring the wave interference phenomenon for effective absorption of NIR light in ultrathin silicon. Particularly, inverted pyramid photonic crystals (PhCs) with nano−micrometer-scale feature sizes are carved directly on silicon. Detailed experimental and theoretical studies are presented by systematically examining the optical properties of PhC-integrated thin silicon substrates (down to a 10 μm thickness). The corresponding maximum photocurrent density for a thin absorber is projected and compared with that predicted by Lambertian's limit. In contrast to traditionally configured microscale inverse pyramids, we show that a small mesa width is critical to achieving high optical performance for a wave-interference-based absorption enhancement. Mesa widths as small as 35 nm are realized over a large wafer-scale fabrication using facile techniques. The optical performance of 10 μm silicon indicates that an ideal photocurrent density approaching 40 mA/cm 2 is feasible. This study indicates that photonic crystals provide strong wave interference in ultrathin silicon, and in particular, we observe high optical absorption even after removing more than 90% of the silicon from conventional "thick" Si wafers.

In this work, a hybrid silicon/polymer super absorber is proposed combining nanowires made from amorphous silicon thin films and coated with a low-band-gap polymer. First, a comprehensive theoretical study of different silicon nanowires shapes and different polymer coatings is conducted using finite difference time-domain (FDTD) simulations to obtain the highest optical absorption (i.e., highest average absorption in the visible and near-infrared range). The optimized structure is then fabricated using a one-step technique for silicon nanowire formation and coated with the optimized polymer. The proposed fabrication technique results in the transformation of silicon from the amorphous to the crystalline state, enhancing its electrical properties. The proposed structure is composed of low-cost materials and fabricated using simple techniques and achieves excellent optical efficiency. This design also has the potential to play a major role in hybrid solar cells as it shows a theoretical maximum short-circuit current of 36.4 mA/cm 2 .

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