Effect of metal doping, doped structure, and annealing under argon on the properties of 30 nm thick ultrathin hematite photoanodes.

The doping of the whole hematite layer with W (9.4%) and the additional doping of the bottom half of the W-doped hematite layer with Sn (8.6%), and the subsequent annealing under argon at 600 °C give rise to large increases in the Fe(2+) concentration (by >∼200 times), carrier density (Cd, by ∼48 times) and current density (i(d), by ∼8 times at 1.23 V vs. RHE, under 1 sun) with respect to those of bare hematite photoanodes. The measured i(d) (0.9 mA cm(-2)) is the highest among those of the ultrathin hematite photoanodes and the measured Cd (3.8 × 10(22) cm(-3)) is the highest among those ever observed for hematite.