Natural Colorants as Photosensitizers for Dye-Sensitized Solar Cells (DSSCs) for Green Enconomy

Abstract

Twenty five natural dyes (D1-D25) were extracted through maceration from local plants species categorized as A= D1-D6, B= D7-D17, C= D18-D20, D= D21-D22, E= D23 and F= D24-D25 on the basis of their parts used for the application in dye sensitized solar cells (DSSCs). The photo-physical and electro-chemical behaviors of natural dye were evaluated through UV-visible spectrophotometry and cyclic voltammetry respectively. The UV-Visible absorption spectrum of the individual dye extracts D1-D25 revealed two distinct bands i.e. First band corresponds to π-π* transition while the second band corresponds to intermolecular charge transfer (ICT) band. Out of all the extracted natural dyes, S. oleracea (D23-E) dye resulted in best absorption at ICT band with λmax = 662 nm having absorbance A= 0.33. Cyclic voltammetry of the dyes D1-D25 was carried out which revealed the distinct oxidation and reduction peaks. The peaks can be seen more prominently among S. oleracea (D23-E), R. tinctorum (D21-D) and H. rosa-sinensis (D1-A) dyes while rest of the dyes exhibited less prominent peaks. The photovoltaic performances of the individual dyes D1-D25 (A-F) were evaluated by fabricating the sandwich-type DSSCs with the extracted natural dyes. TiO2 coated FTO glass slides were prepared for dye adsorption. The J-V profiles showed open circuit voltage values and short circuit current density. The most promising results of photovoltaic parameters were found for solar cell fabricated with D23-E dye with Jsc= 5.38 mA/cm2 and Voc= 0.47 V followed by D21-D (Jsc= 4.14; Voc= 0.36 V) and D1-A (Jsc= 5.48; Voc= 0.36 V) respectively The best sunlight to energy conversion efficiency was obtained from D23-E (η= 1.4%) dye which has better UV absorption and oxidation properties. The respective dye gave high short circuit current density and hence high photon to current efficiency was achieved. Other dyes gave the efficiency in the following order D21-D (R. tinctorum) = 1.1% > D22-D (A. tinctoria)= 1.05% > D1-A (H. rosa sinensis)= 1.02% > D17-B (S. anacardium)= 0.92 > D2-A (B. oleracea var. capitata) & D11-B (P. granatum) = 0.9% > D6-A (R. macdub)= 0.8% > D19-C (B. vulgaris) = 0.7%. Other natural dyes also showed satisfactory results. These natural dyes can easily replace conventional harmful, persistent and expensive metallic and synthetic dyes. Natural dye can be regarded as a promising candidate for low cost DSSCs fabrication with no environmental damage.