Abstract Parallel, close-arranged carbon nanotubes are promising candidates for sunlight trapping. A tandem structure was made by synthesizing aligned carbon nanotube arrays on an Au film. With the nanotube length greater than 10 μm, the tandem structure shows an ultra-high absorption in both the visible and infrared regions. With shorter length (less than 5 μm), infrared reflectance is enhanced due to the presence of the underlying Au film; however, the visible absorptance also decreases at the same time. Carbon nanotubes themselves have no selectivity of solar absorption. They could be used in solar thermal plants where sunlight is collected with high concentration ratios.