Over the past few decades, extensive research on photoelectrochemical (PEC) water splitting has been conducted as a promising solution to meet the increasing demand for cleaner and renewable energy in a sustainable manner. Among the various photocatalysts, hematite (α-Fe₂O₃) has gained significant attention due to its advantageous characteristics, such as a high theoretical solar-to-hydrogen conversion efficiency value, a suitable band gap energy for visible light absorption, chemical stability, and low cost. However, the high PEC potential of α-Fe₂O₃ is hindered by several limitations, including band gap mismatch, short hole diffusion length, and low electrical conductivity. Several modifications are necessary to enhance the viability of α-Fe₂O₃ as an efficient photocatalyst for PEC water splitting. This review article primarily focuses on strategies aimed at improving PEC water oxidation performance, especially by addressing its poor transport behavior through heteroatom doping. In particular, we explore the co-doping approach involving unintentional Sn dopants, which are diffused from the fluorine-doped tin oxide substrate during high-temperature annealing.