Sb powder (99.999 %, Kurt J. Lesker Co. Ltd.) was used as the evaporation source to deposit Sb thin films on FTO/Au substrates via thermal evaporation using the VapourPhase/PicoSphere system (Oxford Vacuum Science Ltd.). Before deposition, FTO glass (FTO TEC 15, Pilkington, Tokyo, Japan) was cleaned sequentially with acetone, a 5% deconex solution in water, distilled water, and isopropanol in an ultrasonic bath for 10 min each, followed by drying under a stream of N2. After cleaning, a 150 nm Au layer with a 10 nm Cr adhesion layer was deposited by sputtering (Safematic CCU-010 sputter coater). Sb layers (240 nm) were evaporated at substrate temperatures of 25 o C and 75 o C with a deposition rate of 0.1 nm/s under a pressure of 1 × 10 -5