DEVELOPMENT OF PHOTOVOLTAIC CELLS FROM BRIDELIA FERRUGINEA B. BIOTEMPLATED NANOPARTICLES

Abstract

Incessant power outage and high cost of power generation which is a perennial challenge facing developing nations necessitated the research herein which is focused on the development of photovoltavic cells from Bridelia ferruginea B. biotemplated nanoparticles. The dye was extracted from Bridelia ferruginea in methanol using Soxhlet apparatus. Adopting the green approach the dye was used to precipitate the nanoparticles/nanocomposite (Ag-ZnO and Cu-ZnO) from their various precursors. Doping of the synthesized material with nitrogen and sulfur was achieved through thermal reduction. Phytochemical constituents of the dye were established following standard protocol and the instrumental analysis using Fourier Transform Infrared (FTIR) Spectroscopy and Gas Chromatography-Mass spectrometry (GC-MS). The synthesized nanoparticles/composites were characterized for their structural, morphological, compositional and optical properties by using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM), Brunauer-Emmette-Teller (BET) and Ultraviolet-Visible Spectroscopy, while the fabricated photoanode and the Dye Sensitized Solar Cell were characterized using Photoelectrochemical (PEC) cell measurement and Electrochemical Impedance spectroscopy (EIS). The phytochemical assay of the dye showed high presence of phenolic compounds, while the antioxidant assay shows its ability to chelate and scavenge metal ions. The XRD results reveal that the nanoparticles/composite are crystalline and have hexagonal crystal structure. SEM confirmed a nodular like shape for ZnO nanoparticles. The nodular particles aggregating into larger molecules with pores upon doping with Cu, Ag, N and S. As the presence of the elements were confirmed by EDX. TEM of ZnO, Ag-ZnO and Cu-ZnO reveal structure of nanoflakes, polyhedral shape of ZnO with Ag dots and spherical particles respectively. The selected area electron diffraction (SAED) shows partial centric illuminated light for Cu-ZnO nanocomposite, which confirmed an irregular orientation of nanocrystals unlike in ZnO nanoparticle and Ag-ZnO nanocomposite. BET show the mesoporous structural nature of the synthesized nanomaterials with specific surface area in the range of 3 to 33 m 2 g -1 . UV-Visible spectrophotometer has been used for the bandgap determination. A bandgap of 4.73 eV was recorded for the dye and 3.24 eV for the ZnO nanoparticles. Doping of synthesized materials with impurities narrowed bandgap within 3.18 and 3.07 eV for the nanocomposites. PEC cell measurements show that the photoanodes of synthesized nanoparticles and nanocomposites have both n- and p- type electrical conductivity except for Cu- ZnO photoanode shows only n-type conductivity. The DSSCs assembled with the Ag-ZnO-N,S - modified photoanode demonstrated a better solar-to-electrical energy conversion efficiency (1.94%) over the other photoanodes, this is attributed to the effect of Ag, N and S dopants on the bandgap of the synthesized nanomaterial used for the fabrication of the photoanode.