Tuning Crystalline Phase and Photoactivity through Charge and Temperature-Assisted Electrodeposition in Bi ₂ Se ₃ Films

High Resolution Image Download MS PowerPoint Slide Bismuth selenide (Bi 2 Se 3 ) is a promising semiconductor material, with applications ranging from thermoelectric devices and topological insulators (TIs) to photocatalysis. Here, Bi 2 Se 3 films were grown on fluorine-doped tin oxide (FTO) substrates using electrodeposition under controlled parameters, such as the electrodeposited charge and electrolyte temperature for solar-driven water splitting, resulting in films with different crystalline phases, morphologies, and PEC performances. Heating the electrolyte promotes the formation of uniform and compact films as well as the coexistence of orthorhombic (O–Bi 2 Se 3 ) and rhombohedral (R–Bi 2 Se 3 ) structures. Notably, PEC measurements demonstrated a significant increase in photocurrent density (up to 0.52 mA/cm 2 at 0.6 V Ag/AgCl ) and lower charge transfer resistance in films deposited with a heated electrolyte. Absorbance and Fourier transform infrared (FTIR) analyses indicate that interactions between the crystalline phases can alter their spectra, possibly due to the formation of an R/O–Bi 2 Se 3 heterophase junction, which contributes to the improvements noted in the PEC performance. Density functional theory (DFT) calculations indicate that R–Bi 2 Se 3 is a TI, while the temperature of O–Bi 2 Se 3 is normal, suggesting that grown films can host electronically active R/O heterophase. These findings highlight the impact of changes in surface morphology, crystal structure, and surface chemistry on enhancing PEC performance, offering a straightforward and scalable approach for optimizing nonoxide semiconductors through electrochemical strategies for solar-driven water splitting.