Hydrothermal Carbon‐Enhanced Flexible Phase Change Films for Solar‐Thermal Conversion and Thermal Regulation

Polyethylene glycol (PEG) shows great potential in solar‐thermal energy conversion and thermal management applications, but its inherent solid‐phase stiffness, liquid‐phase leakage, low light capture efficiency, and low thermal conductivity pose significant challenges for material development. In this article, a solid–solid phase change material (HDPCM) is successfully prepared using block copolymerization, which has a high melting enthalpy of 102.3 J g −1 and excellent thermal energy storage capacity. To further improve its performance, HDPCM is innovatively combined with hydrothermal carbon (HTC), which has excellent thermal stability and efficient solar‐thermal energy conversion capacity. HDPCM‐HTC‐3 has outstanding mechanical properties (tensile strength = 20.27 MPa, and tensile strains = 2750.50%) and solar‐thermal conversion efficiency (83.7%). At the same time, it has excellent thermal stability and remains stable after 101 thermal cycles. In actual thermal management tests, this material can maintain hot water temperature at ≈45 °C for up to 320 s, demonstrating its significant application value in the field of smart temperature control.