Solar water evaporation has been considered as a promising technique to harvest solar energy for practicable water evaporation. While different classes of materials have been exploited as solar absorbers, to date there is no report on using small organic molecules because of their narrow optical absorption spectra. We show here for the first time that full solar spectrum absorption can be conveniently achieved with commercially available small molecules via the formation of charge-transfer complex (CTC) cocrystals between the suitable donor and acceptor molecules. We demonstrate that a porous polymer scaffold loaded with suitable CTC cocrystal can show efficient full solar photothermal conversion leading to a high water evaporation rate of 1.67 kg m–2 h–1 via 90.3% solar conversion under 1 Sun, with practical multiple wastewater purification. This is the first report of a high-performance solar absorber using small organic molecules, suggesting CTC is a promising new class of solar absorbers deserving more attention.