Selective surface

One of the first selective surfaces investigated was a semiconductor-metal tandem[2] – simply copper with a layer of black cupric oxide.

[2][3] Black chromium ("black chrome") and nickel-plated anodized aluminum is another selective surface that is very durable, highly resistant to humidity or oxidizing atmospheres and extreme temperatures, while being able to retain its selective properties, but expensive.

One of the more popular designs – a multi-layer broadband solar absorber – consists of a metal substrate coated with multiple layers of metal and dielectric materials.

While those have to be vacuum-deposited, they have been widely adopted due to their suitability for vacuum tubes.

[2] Selective surfaces are used for other applications than solar thermal collectors, such as low emissivity surfaces used in window glasses, which reflect thermal radiation and have high transmittance factors (being transparent) for visible sunlight.

Solar thermal collector system based on evacuated glass tubes. Sunlight is absorbed by a special material at the center of each tube that has a selective surface. The surface absorbs sunlight nearly completely, and emits very little of the solar heat as thermal radiation. Ordinary black surfaces are also efficient absorbers, but they emit thermal radiation copiously.