Enhancing Water-Splitting Efficiency Using a Zn/Sn-Doped PN Photoelectrode of Pseudocubic α-Fe₂O₃ Nanoparticles

α-Phase hematite photoelectrodes can split water. This material is nontoxic, inexpensive, and chemically stable; its low energy gap of 2.3 eV absorbs light with wavelengths lower than 550 nm, accounting for approximately 30% of solar energy. Previously, we reported polyhedral pseudocubic α-Fe₂O₃ nanocrystals using a facile hydrothermal route to increase spatial charge separation, enhancing the photocurrent of photocatalytic activity in the water-splitting process. Here, we propose a p-n junction structure in the photoanode of pseudocubic α-Fe₂O₃ to improve short carrier diffusion length, which limits its photocatalytic efficiency. We dope Zn on top of an Fe₂O₃ photoanode to form a layer of p-type semiconductor material; Sn is doped from the FTO substrate to form a layer of n-type semiconductor material. The p-n junction, n-type Fe₂O₃:Sn and p-type Fe₂O₃:Zn, increase light absorption and charge separation caused by the internal electric field in the p-n junction.