Photothermal, also known as light-to-heat conversion, a seemingly primitive and ancient means of utilizing solar energy involves harvesting and converting solar irradiation by photothermal materials into heat as terminal energy for beneficial usage. Due to its high energy conversion efficiency, photothermal conversion has gained renewed research interest in the past decade and found itself certain niche applications such as water evaporation and water desalination. In this talk, we will cover (1) droplet light heating system for measuring internal light-to-heat conversion efficiency of a photomaterials; (2) interfacial heating scheme to improve light-to-water-evaporation efficiency; surface wettability is a generally accepted approach to induce self-floating photothermal materials for automated interfacial heating. (3) Rational design of heat barrier to minimize the heat loss to bulk water. Coupled and decoupled water transport channel from heat barrier will be discussed and compared. (4) A polymeric polypyrrole based self-floating and self-healing photothermal material design will be presented in the end.