Inspired by the “Interlocking” Structure in Human Skin: A Universal and Efficient Interfacial Strategy Enabling Flexible Phase Change Materials with a Wide Scope of Customizable Functionalities

Abstract In the quest for effective use and conservation of clean energy, the development of phase change materials (PCMs) that can harvest from multiple ambient energy sources remains challenging. Traditional PCMs rely heavily on a high content of conductive fillers and still lack customizable functionalities, thus limiting their applications. Here, a biomimetic bilayer composite PCM synthesis strategy is demonstrated that uses a solid–liquid two‐step film formation method at extremely low conductive filler loadings (0.56–3.76 wt.%). The interface of the two layers is seamlessly interlocked through a phase separation structure and rough surface of substrates, combined with strong interfacial bonding. The resultant films exhibit excellent flexibility (up to 562%), adjustable strength (>4.3 MPa) and toughness (>16 MJ m −3 ), and high photothermal and electrothermal conversion efficiency (>90%). The films can be applied to solar‐thermoelectric generators (STEG) under the control of light heating. In addition, the magnetic properties and thermoregulatory capacity of the PCMs can be well tailored by using metal functional fillers. This bilayer design opens a new avenue for multifunctional films and makes significant contributions in green chemistry, thermal management, and sustainable energy harvesting and storage.