We further performed capacitance-voltage (CV) and drive-level capacitance profiling (DLCP) measurements to characterize the carrier density in the Sb2Se3-Control and Sb2Se3-Sn (0.5) devices. The measurements were performed utilizing the device structure of Mo/Sb2Se3/TiO2/Al employing a two-electrode system under dark conditions (Figure ). the carrier density of CV profiling (NCV) includes the response of free carriers, bulk defects, and surface defects, while the carrier density obtained from DLCP profiling measurements (NDLCP) is insensitive to surface defects. As seen in Figure , U-shaped profiles of NCV and NDLCP were observed in both Sb2Se3 devices, which arises from the punch-through effect due to the relatively thin nature of the Sb2Se3 films (around 270 nm thickness, see Supplementary Note 1 for further details). We therefore assigned the carrier density based on the lowest point of the DLCP profiles. As mentioned above, an increase in the p-type conductivity of Sb2Se3 with Sn doping treatment has been reported elsewhere. This phenomenon was also found in our Sb2Se3 samples. The carrier density of the Sb2Se3-Sn (0.5) sample is 3.77×10 16 cm -3 , which is almost twice as high as that of the Sb2Se3-Control sample (2.12×10 16 cm -3 ). Considering the higher doping density of the ALD TiO2 (2.6×10 20 cm -3 ), the depletion layer is predominantly located within the Sb2Se3 layer near the Sb2Se3/TiO2 junction. The surface defect density was calculated by subtracting NDLCP from NCV at 0 V and multiplying this value by the depletion layer width (Wd). The corresponding surface defect density for Sb2Se3-Control and Sb2Se3- Sn (0.5) devices were calculated to be 2.67×10 12 cm -2 and 8.64×10 11 cm -2 , respectively. The obtained parameters are summarized in Table . We assume that the suppressed formation of surface defects could be attributed to the accumulation of Sn near the surface of the Sb2Se3-Sn To assess the thermodynamic driving force for charge separation, we performed an open circuit potential (OCP) test. The OCP measurement was conducted in a black box under H2 purging (details in the experimental section). The changes in OCP between dark (OCPdark) and