Structure and optical absorption properties of dyes extracted from selected plant materials for dye sensitized solar cells

Abstract

Sunlight is a natural alternative renewable energy source to expensive hydroelectricity. Dye sensitized solar cells (DSSCs) are third generation solar cells which have the potential to significantly lower the cost associated with the first and second generation solar cells and they can easily be fabricated. A dye is an important component in a DSSC because it absorbs light, produces photoelectrons and facilitates processes of electron transfer to improve the efficiency of electrical energy conversion. It is important to modify the dye as an active component in DSSC for improved performance of optical absorption properties of the dye. Mixing chlorophyll and anthocyanin dyes aims to broaden the absorption wavelength range of visible light. In this study, the chemical structural and optical absorption properties of dyes extracted from selected plant materials for DSSCs were investigated. Anthocyanin dyes from hibiscus flower, chlorophyll dyes from pumpkin and sweet potato leaves and their composites were used as natural sensitizers in the fabrication of DSSCs. The extracted dye powders were characterized using Fourier Transform Infra-Red (FTIR) spectrophotometer to determine their chemical structural properties. The dye extracts and their composites were also characterized using UV-visible spectrophotometer to determine their optical absorption properties. Scanning Electron Microscopy (SEM) and Raman spectroscopy were used to determine the surface morphology and crystalline structure of TiO2 thin film respectively. The performance of the developed cells was measured under one-sun illumination using a solar simulator (AM1.5 100 mWcm-2). Keithley SMU-2450 was used to record the current-voltage (I-V) characteristics of the solar cells. The results reveal that the DSSC fabricated from sweet potato dye extracts had the best power conversion efficiency (PCE) of 0.5 % while that from a mixed dye of sweet potato leaves and hibiscus flower (SH) at a mass ratio of 1:3 gave the best PCE of 1 % with open circuit voltage (Voc) of 0.47 V and short circuit current density (Jsc) of 62 μA/cm2.