The origin of enhanced performance of properties of erbium (Er3+)-doped TiO2 photoanodes used in photo-electrochemical cell (PEC) water-splitting devices and power-conversion efficiency in DSSC devices is presented. Particularly, the dielectric measurements of Er3+-TiO2 conclude that the optimised concentration of Er (0.2% mol)-TiO2 has a better conductivity compared to undoped TiO2. The fabricated PEC devices with Er (0.2% mol)-doped TiO2 photoanode exhibited the higher current density of (9 μA-cm−2) at 1.2 V vs RHE potential which is ≈50% higher than that measured for PEC with undoped-TiO2. This enhancement is corroborated with the EIS measurements presenting lower charge transfer resistance values for devices with Er (0.2% mol)-TiO2. © 2021 Elsevier B.V.