Abstract
Ultrathin (10 to 20 nm thick), polycrystalline films of 
(pyrite) were grown on 
(anatase) by chemical vapor deposition. The 
films were characterized using optical absorption and high‐resolution electron microscopy. Photoelectrochemical solar cells, using 
(anatase) coated with 
ultrathin films, generated high open‐circuit photovoltages, of up to 600 mV, compared with a single crystal of pyrite electrode (200 mV). The photoelectrochemical behavior shows a strong dependence of photovoltage and photocurrent on the pH of the solution. It is explained by electron injection from the conduction band of 
to the conduction band of 
. Regeneration of holes is taking place by electron transfer from the redox system in the electrolyte.