"Though water itself does not absorb much light, and neither does the hydrogel material itself, when the two combine they become strong absorbers, Chen says. That allows the material to harness the energy of the solar photons efficiently and exceed the thermal limit, without the need for any dark dyes for absorption."
So when water is combined with hydrogel, they absorb more light -> more light = more energy -> more energy = more evaporation.
"Though water itself does not absorb much light, and neither does the hydrogel material itself, when the two combine they become strong absorbers, Chen says. That allows the material to harness the energy of the solar photons efficiently and exceed the thermal limit, without the need for any dark dyes for absorption."
So when water is combined with hydrogel, they absorb more light -> more light = more energy -> more energy = more evaporation.