Study of the Enhancement of Cell Performance of Dye Sensitized Solar Cells Sensitized With Nephelium lappaceum (F: Sapindaceae)

We have studied the performance of dye sensitized solar cells sensitized with pigments extracted from the fruit sheath of Nephelium lappaceum (F: Sapindaceae). The pH of the pigment solution used for impregnation was controlled by adding concentrated HCl (50:0.2 v/v). The UV-Vis spectroscopic results revealed that the extract consists of the pigment of Anthocyanin, with an additional absorption peak appearing around 540 nm at a lower pH of the pigment solution. Also the band gap of the pigment was reduced by 1 eV at low pH conditions. The solar cells fabricated with pigment extracted from the fruit sheath of Nephelium lappaceum showed photo-response with the conversion efficiency of 0.26%, with an open-circuit voltage (VOC) of 453 mV, short-circuit current density (ISC) of 1.17 mA cm−2, and fill factor (ff) of 0.48. The conversion efficiency was significantly enhanced when pH of the pigment solution was lowered by adding concentrated HCl. The conversion efficiency of the dye sensitized solar cells (DSSCs) sensitized after HCl treatment of the pigment was increased to 0.56%, with an open-circuit voltage (VOC) of 404 mV, short-circuit current density (ISC) of 2.71 mA cm−2, and fill factor (ff) of 0.35. The HOMO level of the pigment at low pH was shown to be shifted towards more positive values with respect to vacuum level, giving rise to an enhanced DSSC efficiency. The overall efficiency enhancement of the low pH pigment was due to the combined effect of increased UV-Vis absorption and efficient adsorption of dye molecules onto the TiO2 semiconductor surface.