Bridging the gap with a "stepping stone" for more solar energy
Converting the abundant energy from the sun into a form convenient for human use has been a long standing dream for sustainable generation of environmentally clean energy. With the seminal discovery of water splitting by Fujishima and Honda in the early 1970s [1], titanium dioxide (TiO2), an inexpensive white pigment widely used in our daily life, emerged as the premier photocatalysts for enabling solar energy utilization. However, because of its wide intrinsic band gap, TiO2 can absorb only ultraviolet light. This results in less than 1% efficiency for solar energy conversion. Reducing the band gap of TiO2 is the main avenue for boosting the conversion efficiency. In a recent paper to appear in Phys Rev. Lett. [2], Zhu et