Synthesis of Sb2Se3 thin films, sulfurization and material characterization: Sb metal was sputtered from a high purity Sb sputtering target to generate films of 300 nm thickness on quartz substrates for time resolved microwave conductivity (TRMC) measurements, and on Au-coated FTO substrates for dual working electrode measurements. Selenization and sulfurization procedures were the same as used in our previous work. The crystal structure of Sb2Se3 and sulfur-treated Sb2Se3 was determined by X-ray diffraction using a Rigaku SmartLab instrument (Cu Kα radiation). UV-vis absorption spectra were measured using a PerkinElmer Lambda 950 spectrometer fitted with an integrating sphere. X-ray photoelectron spectroscopy (XPS) was conducted using a Physical Electronics (PHI) Quantum 2000 X-ray photoelectron spectrometer featuring monochromatic Al-Kα radiation, generated from an electron beam operated at 15 kV and 32.3 W. The energy scale of the instrument was calibrated using Au and Cu reference samples. The analysis was conducted at 1×10 -6 Pa, with an electron take off angle of 45° and a pass energy of 46.00 eV. Charge compensation during the measurement was achieved using a low energy electron source. The sputter depth profile was performed using Ar ions (2 kV potential) on an area of approximately 4 mm 2 . Surface elemental concentrations were determined using the instrument specific sensitivity factors for calculation. The core level emissions were fitted to deconvolute spectra with contributions from multiple elements using Voigt profiles (GL30) after Shirley background subtraction.