A simplistic and low-cost method
that dramatically improves the
performance of solution-grown hematite photoanodes for solar-driven
water splitting through incorporation of nanohybrid metal oxide overlayers
was developed. By heating the α-Fe
2
O
3
/SnO
2
–TiO
2
electrode in an inert atmosphere,
such as argon or nitrogen, the photocurrent increased to over 2 mA/cm
2
at 1.23 V versus a reversible hydrogen electrode, which is
10 times higher than that of pure hematite under 1 sun (100 mW/cm
2
, AM 1.5G) light illumination. For the first time, we found
a significant morphological difference between argon and nitrogen
gas heat-treated hematite films and discussed the consequences for
photoresponse. The origin for the enhancement, probed via theoretical
modeling, stems from the facile incorporation of low formation energy
dopants into the Fe
2
O
3
layer at the interface
of the metal oxide nanohybrid overlayer, which decreases recombination
by increasing the electrical conductivity of Fe
2
O
3
. These dopants diffuse from the overlayer into the α-Fe
2
O
3
layer readily under inert gas heat treatment.
This simple yet effective strategy could be applied to other dopants
to increase hematite performance for solar energy conversion applications.