Modified annealing approach for preparing multi-layered hematite thin films for photoelectrochemical water splitting

Abstract Multi-layered hematite (α-Fe2O3) films were prepared on fluorine-doped tin oxide (FTO) using the dip coating method. The first three layers of the films were annealed at 500 °C and fourth layers at 500, 600, 700, 750 and 800 °C respectively, and their photoelectrochemical (PEC) performance was investigated. Films annealed at 750 °C recorded the best performance, producing 0.19 mA/cm2 photocurrent at 1.23 V vs reversible hydrogen electrode (RHE); 5.3 times more than what was recorded for films sintered at 500 °C, and the onset potential yielded a cathodic shift of 300 mV. The enhanced performance was linked to improved crystallization, absorption coefficient, lowered flat band potential, increased charge carrier density, decreased charge transfer resistance at the solid/liquid interface and increased surface states capacitance for films annealed at 750 °C. The PEC performance of multi-layered α-Fe2O3 films could be improved by annealing the last layers at elevated temperatures without damaging the conducting substrates.