Near perfect flexible solar-thermal layers with high absorption and thermal conductance: Optimization study of flexible vertically aligned carbon nanotube (VACNT) arrays through optical and thermal aspects

Flexible super-black absorbers with high absorbance and thermal conductance show great potential for solar thermal applications. Vertically aligned carbon nanotube (VACNT) arrays are widely used due to their unique structure, offering excellent optical and energy transfer properties. The challenge is to enhance both absorbance and thermal conductance while maintaining flexibility. We optimize VACNT from optical and thermal perspectives, proposing a flexible VACNT for efficient solar thermal conversion and energy transfer. Using Tracepro software, we established an optical model of VACNT, and with MATLAB, we developed a thermal transfer model. We examined how structural parameters such as single-tube diameter, length, spacing, and incident angle affect Equivalent absorption and thermal conductance. To increase flexibility and adaptability while maintaining performance, we introduced a flexible substrate into the VACNT and studied the effects of different flexible media on the performance of the carbon nanotubes. Results indicate that the optimal parameters are a height of 1 μm, a single-tube diameter of 200 nm, and a spacing of 200 nm. Under these optimal conditions, VACNT achieved a thermal conductance of 1043.07 W/K and an Equivalent absorption of 98.60%. With PDMS as the medium, the highest Equivalent absorption of VACNT reached 99.51%. Thus, this absorber layer achieves synergistic enhancement and significant improvements in solar absorption, photothermal conversion, and thermal transfer, providing a reference for next-generation flexible photothermal materials.