Bio‐Inspired Ultrathin Perfect Absorber for High‐Performance Photothermal Conversion

Abstract Ultrathin perfect absorber (UPA) enables efficient photothermal conversion (PC) in renewable chemical and energy systems. However, it is challenging so far to obtain efficient absorption with thickness significantly less than the wavelength, especially considering the common view that an ultrathin film can absorb at most 50% of incident light. Here, a highly light‐absorbing and mechanically stable UPA is reported by learning from the honeycomb mirror design of the crab compound eyes. With the hollow apertures enclosed by the self‐supporting ultrathin film of reduced graphene oxide and gold nanoparticles, the absorber achieves spoof‐plasmon enhanced broadband absorption in solar spectrum and low radiative decay in infrared. Specifically, a strong absorption (87%) is realized by the apertures with cross‐section thickness of 1/20 of the wavelength, which is 7.3 times stronger than a planar counterpart with the identical material. Its high PC efficiency up to 64%, with hot‐electron temperature as high as 2344 K, is also experimentally demonstrated. Utilizing its low thermal mass nature, a high‐speed visible‐to‐infrared converter is constructed. The absorber can enable high‐performance PC processes for future interfacial catalysis and photon‐detection.