  High-temperature concentrating solar power (CSP) system is capable of
harvesting and storing solar energy as heat towards cost-effective dispatchable
solar electricity. Solar selective coating is a critical component to boost its
efficiency by maximizing solar absorptance and minimizing thermal emittance
losses. However, maintaining a high solar-thermal conversion efficiency >90%
for long-term operation at >750 degrees C remains a significant challenge.
Herein, we report spray-coated spinel Cu-Mn-Cr oxide nanoparticle-pigmented
solar selective coatings on Inconel tube sections maintaining >94% efficiency
at 750 degrees C and >92.5% at 800 degrees C under 1000x solar concentration
after 60 simulated day-night thermal cycles in air, each cycle comprising 12h
at 750 degrees C/800 degrees C and 12h cooling to 25 degrees C. The solar
spectral selectivity is intrinsic to the band-to-band and d-d transitions of
non-stoichiometric spinel Cu-Mn-Cr oxide nanoparticles by balancing the lattice
site inversion of Cu2+ and Mn3+ on tetrahedral vs. octahedral sites. This
feature offers a large fabrication tolerance in nanoparticle volume fraction
and coating thickness, facilitating low-cost and scalable spray-coated
high-efficiency solar selective absorbers for high-temperature CSP systems.
