Dye pH effect on photoelectric parameters of natural photosensitizer pigment extracted from Alstonia boonei for dye-sensitized solar cells

Abstract

The study was carried out to ascertain the effect of pH on sensitizing ability of a natural photosensitizer dye. Natural dye extracted from Alstonia boonei (Stool wood) leaves was assessed for its chemical compositions using IR, UV and GCMS and revealed the presence of many bioactive compounds that promote sensitizing ability. The pH of 100 mL portions of the dye was adjusted to 1.30, 3.00, 5.68 and 6.33, then used to sensitize solar cells fabricated using the screen printing method. These dye-sensitized solar cells (DSSCs) were characterized using UVspectroscopy, XRD, SEM and solar simulation, from which the I-V properties, fill factor (FF) and efficiency of the cells were determined. The photoelectrical performance of the cells showed an open-circuit voltage (Voc) of 0.490 V, short-circuit current density Jsc of 0.67 mA/cm2, a fill factor (FF) of 0.701 and a conversion efficiency of 0.23% for the DSSC at dye pH 1.30, Voc of 0.469 V, Jsc of 3.10 mA/cm2, an FF of 0.671 and a conversion efficiency of 0.980% for DSSC at dye pH of 3.0, Voc of 0.48 V, Jsc of 3.0 mA/cm2 an FF of 0.673 and a conversion efficiency of 0.969% for DSSC at dye pH 5.63 and Voc of 0.51 V, Jsc of 0.33 mA/cm2, FF of 0.309 and conversion efficiency of 0.052. The cells showed absorption at the UV, visible and near infrared (NIR) with maximum absorption of 1.298, 1.963, 1.413 and 1.589 at lambda maxima (λmax, nm) at 299.50, 307.84, 307.84 and 307.84, respectively, for DSSCs at dye pH values of 1.30, 3.00, 5.63 and 6.33, respectively. Most of the parameters tested showed that there was better conversion efficiency for the cells at a dye pH of 3. This affirms that modifying the pH of sensitizer dyes enhances the absorption capacity and overall cell efficiency.