The most used semiconductor in the DSSC photoanode is titanium dioxide nanoparticles (TiO₂ NPs), which are usually synthesized using chemical or physical processes. The main problem with these processes is that they are less environmentally friendly and may impose problems on the environment. Therefore, there is a need to synthesize TiO₂ NPs in an eco-friendly way via a green method. In this study, gambier leaves extract is used as environmentally friendly medium in the green synthesis of TiO₂ NPs. The active chemicals and functional groups of the plant extracts are examined using liquid chromatography-mass spectroscopy (LCMS) and infrared spectroscopy (FTIR). The obtained TiO₂ NPs are characterized using ultraviolet spectroscopy (UV-DRS), X-ray diffraction (XRD), and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM/EDS), Raman spectroscopy, and high-resolution transmission electron microscopy equipped selected area diffraction (HRTEM/SAED). The results from the green syntheses are further used as a semiconductor in DSSC device. The highest efficiency of 4.40% is obtained from the TiO₂ NPs synthesized using gambier leaves extract containing 50% acetylacetone, higher than that of commercial TiO₂ NPs (2.83%). These findings provide insight for future sustainability and the possibility to open new door for more environmentally friendly green synthesis of nanomaterials.