Harnessing Jahn‐Teller Distortion via Cation Disorder Engineering for Broadband Solar Absorptance

Abstract Materials with broadband high solar absorptance and excellent thermal stability are crucial for solar energy utilization. The distinct spectral separation between electronic transitions and carrier absorption leads to limited broadband absorption efficiency in ceramics. Strategic design of structural units with tunable absorption and bandwidth is essential to overcome spectral limitations for broadband solar harvesting. This study establishes an engineering strategy that synergistically exploits cation disorder and Jahn‐Teller distortions in spinel to achieve enhanced absorption. Through strategic incorporation of [CuO 6 ] and [CuO 4 ] structural units into MgAl 2 O 4 , Mg 0.4 Cu 0.6 Al 2 O 4 achieves a remarkable solar absorptance of 94.9% over 0.2–8 µm and demonstrates impressive thermal stability with less than 1.5% absorptance loss after annealing at 1300 °C for 100 h. The enhanced absorption is attributed to Jahn‐Teller distortions in both [CuO 4 ] tetrahedra and [CuO 6 ] octahedra, which induce significant multiple splitting of Cu‐3d orbitals, enhancing electronic transitions and carrier absorption. The developed material exhibits broadband solar absorptance, high‐temperature stability, and low density among oxide ceramics, making it a promising candidate for concentrated solar absorbers. These findings provide fundamental insights into the design of high‐performance solar absorbers through targeted manipulation of structural units and coordination environments.